Snake
Overview
Snakes are elongate, legless, carnivorous
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...

 reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s of the suborder Serpentes that can be distinguished from legless lizard
Legless lizard
Legless lizard may refer to any of several groups of lizards which have independently lost limbs or reduced them to the point of being of no use in locomotion. It is the common name for the family Pygopodidae, but often refers to other groups, such as limbless anguids, depending upon the region of...

s by their lack of eyelids and external ears. Like all squamates
Squamata
Squamata, or the scaled reptiles, is the largest recent order of reptiles, including lizards and snakes. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the...

, snakes are ectothermic, amniote
Amniote
The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...

 vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s covered in overlapping scales
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...

. Many species of snakes have skulls with many more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with their highly mobile jaws
Cranial kinesis
Cranial kinesis is the term for significant movement of skull bones relative to each other in addition to movement at the joint between the upper and lower jaw. It is usually taken to mean relative movement between the upper jaw and the braincase....

. To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one functional lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

.
Encyclopedia
Snakes are elongate, legless, carnivorous
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...

 reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s of the suborder Serpentes that can be distinguished from legless lizard
Legless lizard
Legless lizard may refer to any of several groups of lizards which have independently lost limbs or reduced them to the point of being of no use in locomotion. It is the common name for the family Pygopodidae, but often refers to other groups, such as limbless anguids, depending upon the region of...

s by their lack of eyelids and external ears. Like all squamates
Squamata
Squamata, or the scaled reptiles, is the largest recent order of reptiles, including lizards and snakes. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the...

, snakes are ectothermic, amniote
Amniote
The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...

 vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s covered in overlapping scales
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...

. Many species of snakes have skulls with many more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with their highly mobile jaws
Cranial kinesis
Cranial kinesis is the term for significant movement of skull bones relative to each other in addition to movement at the joint between the upper and lower jaw. It is usually taken to mean relative movement between the upper jaw and the braincase....

. To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one functional lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

. Some species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...

.

Living snakes are found on every continent except Antarctica and on most islands. Fifteen families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 are currently recognized, comprising 456 genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 and over 2,900 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

. They range in size from the tiny, 10 cm-long thread snake
Leptotyphlops carlae
Barbados Threadsnake is a species of blind threadsnake. It is the smallest snake species currently known to exist. This member of the Leptotyphlopidae family is found on the Caribbean island of Barbados....

 to pythons and anaconda
Anaconda
An anaconda is a large, non-venomous snake found in tropical South America. Although the name actually applies to a group of snakes, it is often used to refer only to one species in particular, the common or green anaconda, Eunectes murinus, which is one of the largest snakes in the world.Anaconda...

s of up to 7.6 metres (24.9 ft) in length. The fossil species Titanoboa cerrejonensis was 15 metres (49.2 ft) long. Snakes are thought to have evolved from either burrowing or aquatic lizards during the mid-Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 period, and the earliest known fossils date to around 112 Ma ago. The diversity of modern snakes appeared during the Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...

 period (c 66 to 56 Ma ago).

Most species are nonvenomous and those that have venom use it primarily to kill and subdue prey rather than for self-defense. Some possess venom potent enough to cause painful injury or death
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....

 to humans. Nonvenomous snakes either swallow prey alive or kill by constriction
Constriction
Constriction is a method used by various snake species to kill their prey. Although some species of venomous and mildly-venomous snakes do use constriction to subdue their prey, most snakes which use constriction lack venom. The snake initially strikes at its prey and holds on, pulling the prey...

.

Etymology

The English word snake comes from Old English snaca, itself from Proto-Germanic *snak-an- (cf. German
German language
German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....

 Schnake "ring snake," Swedish
Swedish language
Swedish is a North Germanic language, spoken by approximately 10 million people, predominantly in Sweden and parts of Finland, especially along its coast and on the Åland islands. It is largely mutually intelligible with Norwegian and Danish...

 snok "grass snake"), from Proto-Indo-European
Proto-Indo-European language
The Proto-Indo-European language is the reconstructed common ancestor of the Indo-European languages, spoken by the Proto-Indo-Europeans...

 root *(s)nēg-o- "to crawl, creep," which also gave sneak as well as Sanskrit
Sanskrit
Sanskrit , is a historical Indo-Aryan language and the primary liturgical language of Hinduism, Jainism and Buddhism.Buddhism: besides Pali, see Buddhist Hybrid Sanskrit Today, it is listed as one of the 22 scheduled languages of India and is an official language of the state of Uttarakhand...

 nāgá "snake." The word ousted adder, as adder went on to narrow in meaning, though in Old English næddre was the general word for snake. The other term, serpent, is from French, ultimately from Indo-European *serp- (to creep), which also gave Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

  érpo (ερπω) "I crawl."

Evolution

Note: the tree only indicates relationships, not evolutionary branching times.

The fossil record of snakes is relatively poor because snake skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...

s are typically small and fragile, making fossilization uncommon. Fossils readily identifiable as snakes (though often retaining hind limbs) first appear in the fossil record during the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 period. The earliest known snake fossils come from sites in Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...

 and Algeria
Algeria
Algeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...

, represented by the genera Coniophis and Lapparentophis, respectively. These fossil sites have been tentatively dated to the Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...

 or Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...

 age of the late Cretaceous, between 112 and 94 Ma ago. However, an even older age has been suggested for one of the Algerian sites, which may be as old as the Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...

, 125-112 Ma ago.

Based on comparative anatomy
Comparative anatomy
Comparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:...

, there is consensus that snakes descended from lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...

s. Pythons and boas—primitive groups among modern snakes—have vestigial hind limbs: tiny, clawed digits known as anal spur
Anal spur
Pelvic spurs are the externally visible portion of the vestigial remnants of legs found on each side of the vent in primitive snakes, such as boas and pythons. The remnants of a pelvis and femur, which have no connection with the spine, simply "float" in the muscle mass. The femur protrudes from...

s, which are used to grasp during mating. The Leptotyphlopidae
Leptotyphlopidae
The Leptotyphlopidae are a family of snakes found in North and South America, Africa, and Asia. All are fossorial and adapted to burrowing, feeding on ants and termites...

 and Typhlopidae
Typhlopidae
The Typhlopidae are a family of blind snakes. They are found mostly in the tropical regions of Africa, Asia, the Americas, and all mainland Australia and various islands. The rostral scale overhangs the mouth to form a shovel like burrowing structure. They live underground in burrows, and since...

 groups also possess remnants of the pelvic girdle, sometimes appearing as horny projections when visible.

Frontal limbs are nonexistent in all known snakes. This is caused by the evolution of Hox genes, controlling limb morphogenesis
Morphogenesis
Morphogenesis , is the biological process that causes an organism to develop its shape...

. The axial skeleton of the snakes’ common ancestor, like most other tetrapods, had regional specializations consisting of cervical (neck), thoracic (chest), lumbar (lower back), sacral (pelvic), and caudal (tail) vertebrae. Early in snake evolution, the Hox gene expression in the axial skeleton responsible for the development of the thorax became dominant. As a result, the vertebrae anterior to the hindlimb buds (when present) all have the same thoracic-like identity (except from the atlas
Atlas (anatomy)
In anatomy, the atlas is the most superior cervical vertebra of the spine.It is named for the Atlas of Greek mythology, because it supports the globe of the head....

, axis
Axis (anatomy)
In anatomy, the second cervical vertebra of the spine is named the axis or epistropheus.It forms the pivot upon which the first cervical vertebra , which carries the head, rotates....

, and 1–3 neck vertebrae). In other words, most of a snake’s skeleton is an extremely extended thorax. Ribs are found exclusively on the thoracic vertebrae. Neck, lumbar and pelvic vertebrae are very reduced in number (only 2–10 lumbar and pelvic vertebrae are present), while only a short tail remains of the caudal vertebrae. However, the tail is still long enough to be of important use in many species, and is modified in some aquatic and tree-dwelling species.

Modern snakes greatly diversified during the Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...

. This occurred alongside the adaptive radiation
Adaptive radiation
In evolutionary biology, adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different...

 of mammals, following the extinction of (non-avian) dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s. The colubrids, one of the more common snake groups, became particularly diverse due to preying on rodents, an especially successful mammal group. There are over 2,900 species of snakes ranging as far northward as the Arctic Circle
Arctic Circle
The Arctic Circle is one of the five major circles of latitude that mark maps of the Earth. For Epoch 2011, it is the parallel of latitude that runs north of the Equator....

 in Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...

 and southward through Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 and Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...

. Snakes can be found on every continent (with the exception of Antarctica), in the sea, and as high as 16,000 feet (4,900 m) in the Himalayan Mountains of Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

. There are numerous islands from which snakes are absent, such as Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

, Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

, and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

.

Origins

The origin of snakes remains an unresolved issue. There are two main hypotheses competing for acceptance.

Burrowing Lizard Hypothesis
There is fossil evidence to suggest that snakes may have evolved from burrowing lizards, such as the varanids (or a similar group) during the Cretaceous Period
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

. An early fossil snake, Najash rionegrina
Najash rionegrina
Najash is an extinct genus of basal snake. Like a number of other Cretaceous snakes , it had two hind-limbs. The fossils were found in a land-based deposit, and the robust backbone vertebrae and rear legs of the snake were adapted to a burrowing, subterranean environment...

, was a two-legged burrowing animal with a sacrum
Sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...

, and was fully terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...

. One extant analog of these putative ancestors is the earless monitor Lanthanotus
Lanthanotidae
The Earless monitor lizard is a semi-aquatic, brown lizard native to northern Borneo. It is the only species in the family Lanthanotidae, a group related to the true monitor lizards, as well as to the beaded lizards....

of Borneo
Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....

 (though it also is semiaquatic
Aquatic animal
An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...

). Subterranean species evolved bodies streamlined for burrowing, and eventually lost their limbs. According to this hypothesis, features such as the transparent, fused eyelids (brille
Brille
The brille is the layer of transparent, immovable disc-shaped skin or scale covering the eyes of some animals for protection, especially in animals without eyelids. The brille has evolved from a fusion of the upper and lower eyelids...

) and loss of external ears evolved to cope with fossorial
Fossorial
A fossorial organism is one that is adapted to digging and life underground such as the badger, the naked mole rat, and the mole salamanders Ambystomatidae...

 difficulties, such as scratched cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

s and dirt in the ears. Some primitive snakes are known to have possessed hindlimbs, but their pelvic bones lacked a direct connection to the vertebrae. These include fossil species like Haasiophis
Haasiophis
Haasiophis, consisting of the sole species Haasiophis terrasanctus, is an extinct genus of snakes with hind limbs. It is one of three genera of Cenomanian snakes known to have possessed hindlimbs.-Etymology:...

, Pachyrhachis
Pachyrhachis
Pachyrhachis is an extinct genus of snake with well developed hind legs known from fossils discovered Ein Yabrud, near Ramallah, in the central West Bank. It is one of three genera of Cenomanian snakes with hindlimbs. Many of today's modern pythons and boas still have small bone spurs, where limbs...

and Eupodophis
Eupodophis
Eupodophis is an extinct genus of snake from the Late Cretaceous period. It has two small hind legs and is considered a transitional form between Cretaceous lizards and limbless snakes. The feature, described as vestigial, was most likely useless to Eupodophis. The type species Eupodophis...

, which are slightly older than Najash.
Aquatic Mosasaur Hypothesis
An alternative hypothesis, based on morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

, suggests the ancestors of snakes were related to mosasaur
Mosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...

s—extinct aquatic
Aquatic animal
An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...

 reptiles from the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

—which in turn are thought to have derived from varanid lizards
Monitor lizard
Monitor lizards are usually large reptiles, although some can be as small as in length. They have long necks, powerful tails and claws, and well-developed limbs. Most species are terrestrial, but arboreal and semiaquatic monitors are also known...

. According to this hypothesis, the fused, transparent eyelids of snakes are thought to have evolved to combat marine conditions (corneal water loss through osmosis), and the external ears were lost through disuse in an aquatic environment. This ultimately lead to an animal similar to today's sea snakes. In the Late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

, snakes recolonized land, and continued to diversify into today's snakes. Fossilized snake remains are known from early Late Cretaceous marine sediments, which is consistent with this hypothesis; particularly so, as they are older than the terrestrial Najash rionegrina. Similar skull structure, reduced or absent limbs, and other anatomical features found in both mosasaurs and snakes lead to a positive cladistical
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...

 correlation, although some of these features are shared with varanids.

Genetic studies in recent years have indicated snakes are not as closely related to monitor lizards as was once believed—and therefore not to mosasaurs, the proposed ancestor in the aquatic scenario of their evolution. However, more evidence links mosasaurs to snakes than to varanids. Fragmented remains found from the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 and Early Cretaceous indicate deeper fossil records for these groups, which may potentially refute either hypothesis.

Taxonomy

All modern snakes are grouped within the suborder
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 Serpentes in Linnean taxonomy, part of the order
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 Squamata
Squamata
Squamata, or the scaled reptiles, is the largest recent order of reptiles, including lizards and snakes. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the...

, though their precise placement within squamates
Squamata
Squamata, or the scaled reptiles, is the largest recent order of reptiles, including lizards and snakes. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the...

 is controversial.

There are two infraorders of Serpentes: Alethinophidia
Alethinophidia
The Alethinophidia are an infraorder of snakes that includes all snakes other than blind snakes and thread snakes. Currently, 15 families are recognized, including 9 subfamilies and 316 genera.* Family: Acrochordidae Bonaparte, 1831 -- wart snakes...

 and Scolecophidia
Scolecophidia
The Scolecophidia are an infraorder of snakes. They range in size from 10-100 cm in length, but may only be as small as 2 mm. All are fossorial. Currently, 3 families and 12 genera are recognized.-Families:-See also:...

. This separation is based on morphological
Comparative anatomy
Comparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:...

 characteristics and mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...

 sequence similarity. Alethinophidia is sometimes split into Henophidia
Henophidia
Henophidia is a superfamily of the suborder Serpentes that contains boas, pythons and other snakes. Snakes belonging to superfamily Henophidia are considered to be more primitive than those belonging to the other superfamilies - namely, Typhlopoidea and Xenophidia.-Etymology:Henophidia comes from...

 and Caenophidia, with the latter consisting of "colubroid" snakes (colubrids, vipers, elapids, hydrophiids, and attractaspids) and acrochordids, while the other alethinophidian families comprise Henophidia. While not extant today, the Madtsoiidae
Madtsoiidae
Madtsoiidae are an extinct group of mostly Gondwanan snakes with a fossil record extending from early Cenomanian to late Pleistocene strata located in South America, Africa, India, Australia and Southern Europe...

, a family of giant, primitive, python-like snakes, was around until 50,000 years ago in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, represented by genera such as Wonambi
Wonambi
Wonambi is a genus that consisted of two species of very large snakes. These species were not pythons, like Australia's other large constrictors of the genus Morelia, and are now a member of an extinct family Madtsoiidae...

.

There are numerous debates in the systematics within the group. For instance, many sources classify Boidae and Pythonidae as one family, while some keep the Elapidae
Elapidae
Elapidae is a family of venomous snakes found in tropical and subtropical regions around the world, terrestrially in Asia, Australia, Africa, North America and South America and aquatically in the Pacific and Indian Oceans...

 and Hydrophiidae (sea snakes) separate for practical reasons despite their extremely close relation.

Recent molecular studies support the monophyly
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...

 of the clades of modern snakes, scolecophidians, typhlopids + anomalepidids, alethinophidians, core alethinophidians, uropeltids (Cylindrophis, Anomochilus, uropeltines), macrostomatans, booids, boids, pythonids and caenophidians.

Families

Infraorder Alethinophidia
Alethinophidia
The Alethinophidia are an infraorder of snakes that includes all snakes other than blind snakes and thread snakes. Currently, 15 families are recognized, including 9 subfamilies and 316 genera.* Family: Acrochordidae Bonaparte, 1831 -- wart snakes...

15 families
Family Taxon author Genera Species Common name Geographic range
Acrochordidae
Acrochordidae
The Acrochordidae are a monotypic family created for the genus Acrochordus. This is a group of primitive aquatic snakes found in Australia and Indonesia. Currently, 3 species are recognized.-Description:...

Bonaparte
Charles Lucien Bonaparte
Charles Lucien Jules Laurent Bonaparte, 2nd Prince of Canino and Musignano was a French naturalist and ornithologist.-Biography:...

, 1831
1 3 Wart snakes Western India and Sri Lanka through tropical Southeast Asia to the Philippines, south through the Indonesian/Malaysian island group to Timor, east through New Guinea to the northern coast of Australia to Mussau Island
Mussau Island
Mussau Island is the largest island of St. Matthias Islands, Papua New Guinea, at . It is one of the northernmost islands of Papua New Guinea....

, the Bismark Archipelago and Guadalcanal Island in the Solomon Islands.
Aniliidae
Aniliidae
The Aniliidae are a monotypic family created for the monotypic genus Anilius that contains the species A. scytale, found in South America. This snake possesses a vestigial pelvic girdle that is visible as a pair of cloacal spurs. It is ovoviviparous. The diet consists mainly of amphibians and...

Stejneger
Leonhard Hess Stejneger
Leonhard Hess Stejneger was a Norwegian-born American ornithologist, herpetologist and zoologist. Stejneger specialized in vertebrate natural history studies. He gained his greatest reputation with reptiles and amphibians....

, 1907
1 1 False coral snake Tropical South America.
Anomochilidae Cundall, Wallach, 1993 1 2 Dwarf pipe snakes West Malaysia and on the Indonesian island of Sumatra
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...

.
Atractaspididae
Atractaspididae
The Atractaspididae are a family of snakes found in Africa and the Middle East. Currently, 12 genera are recognized.-Description:This family includes many genera formerly classed in other families, on the basis of fang type. It includes fangless , rear-fanged , fixed-fanged , and viper-like species...

Günther
Albert C. L. G. Günther
Albert Karl Ludwig Gotthilf Günther FRS, also Albert Charles Lewis Gotthilf Günther , was a German-born British zoologist, ichthyologist, and herpetologist....

, 1858
12 64 Burrowing asps Africa and the Middle East.
Boidae Gray
John Edward Gray
John Edward Gray, FRS was a British zoologist. He was the elder brother of George Robert Gray and son of the pharmacologist and botanist Samuel Frederick Gray ....

, 1825
8 43 Boas Northern, Central and South America, the Caribbean, southeastern Europe and Asia Minor, Northern, Central and East Africa, Madagascar and Reunion Island, the Arabian Peninsula, Central and southwestern Asia, India and Sri Lanka, the Moluccas and New Guinea through to Melanesia and Samoa.
Bolyeriidae Hoffstetter
Robert Hoffstetter
Robert Hoffstetter was a 20th century taxonomist who was influential in categorizing reptiles. He labeled the Bolyeriidae family of snakes.-References:...

, 1946
2 2 Splitjaw snakes Mauritius
Mauritius
Mauritius , officially the Republic of Mauritius is an island nation off the southeast coast of the African continent in the southwest Indian Ocean, about east of Madagascar...

.
Colubridae Oppel
Nicolaus Michael Oppel
Nicolaus Michael Oppel was a German naturalist. He was a student of, and worked as an assistant to, André Marie Constant Duméril at the Muséum national d'histoire naturelle in Paris, France, cataloging and classifying species of reptiles...

, 1811
304 1938 Typical snakes Widespread on all continents, except Antarctica.
Cylindrophiidae Fitzinger
Leopold Fitzinger
Leopold Joseph Franz Johann Fitzinger was an Austrian zoologist.Fitzinger was born in Vienna and studied botany at the university of Vienna under Nikolaus Joseph von Jacquin...

, 1843
1 8 Asian pipe snakes Sri Lanka east through Myanmar, Thailand, Cambodia, Vietnam and the Malay Archipelago to as far east as Aru Islands
Aru Islands
The Aru Islands are a group of about ninety-five low-lying islands in the Maluku province of eastern Indonesia. They also form a regency of Indonesia.-Geography:...

 off the southwestern coast of New Guinea. Also found in southern China (Fujian, Hong Kong and on Hainan Island) and in Laos.
Elapidae
Elapidae
Elapidae is a family of venomous snakes found in tropical and subtropical regions around the world, terrestrially in Asia, Australia, Africa, North America and South America and aquatically in the Pacific and Indian Oceans...

Boie
Friedrich Boie
Friedrich Boie was a German scientist and brother of Heinrich Boie. He was born at Meldorf in Holstein and died at Kiel....

, 1827
61 235 Elapids On land, worldwide in tropical and subtropical regions, except in Europe. Sea snakes occur in the Indian Ocean and the Pacific.
Loxocemidae
Loxocemidae
The Loxocemidae are a monotypic family of snakes created for the monotypic genus Loxocemus that contains the species L. bicolor found in Central America. Loxocemidae is the smallest snake family, having just one species and one genera. No subspecies are currently recognized.-Description:Being the...

Cope
Edward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...

, 1861
1 1 Mexican burrowing snake Along the Pacific versant from Mexico south to Costa Rica.
Pythonidae Fitzinger
Leopold Fitzinger
Leopold Joseph Franz Johann Fitzinger was an Austrian zoologist.Fitzinger was born in Vienna and studied botany at the university of Vienna under Nikolaus Joseph von Jacquin...

, 1826
8 26 Pythons Subsaharan Africa, India, Myanmar, southern China, Southeast Asia and from the Philippines southeast through Indonesia to New Guinea and Australia.
Tropidophiidae Brongersma, 1951 4 22 Dwarf boas From southern Mexico and Central America, south to northwestern South America in Colombia, (Amazonian
Amazon Basin
The Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...

) Ecuador and Peru, as well as in northwestern and southeastern Brazil. Also found in the West Indies.
Uropeltidae Müller
Johannes Peter Müller
Johannes Peter Müller , was a German physiologist, comparative anatomist, and ichthyologist not only known for his discoveries but also for his ability to synthesize knowledge.-Early years and education:...

, 1832
8 47 Shield-tailed snakes Southern India and Sri Lanka.
Viperidae
Viperidae
The Viperidae are a family of venomous snakes found all over the world, except in Antarctica, Australia, Ireland, Madagascar, Hawaii, various other isolated islands, and above the Arctic Circle. All have relatively long, hinged fangs that permit deep penetration and injection of venom. Four...

Oppel
Nicolaus Michael Oppel
Nicolaus Michael Oppel was a German naturalist. He was a student of, and worked as an assistant to, André Marie Constant Duméril at the Muséum national d'histoire naturelle in Paris, France, cataloging and classifying species of reptiles...

, 1811
32 224 Vipers The Americas, Africa and Eurasia.
Xenopeltidae
Xenopeltidae
The Xenopeltidae are a monotypic family of snakes created to the genus Xenopeltis, which is found in Southeast Asia. Its members are known for their highly iridescent scales. Currently, two species are recognized and no subspecies.-Description:...

Bonaparte
Charles Lucien Bonaparte
Charles Lucien Jules Laurent Bonaparte, 2nd Prince of Canino and Musignano was a French naturalist and ornithologist.-Biography:...

, 1845
1 2 Sunbeam snakes Southeast Asia from the Andaman
Andaman Islands
The Andaman Islands are a group of Indian Ocean archipelagic islands in the Bay of Bengal between India to the west, and Burma , to the north and east...

 and Nicobar Islands
Nicobar Islands
The Nicobar Islands are an archipelagic island chain in the eastern Indian Ocean...

, east through Myanmar to southern China, Thailand, Laos, Cambodia, Vietnam, the Malay Peninsula and the East Indies to Sulawesi
Sulawesi
Sulawesi is one of the four larger Sunda Islands of Indonesia and is situated between Borneo and the Maluku Islands. In Indonesia, only Sumatra, Borneo, and Papua are larger in territory, and only Java and Sumatra have larger Indonesian populations.- Etymology :The Portuguese were the first to...

, as well as the Philippines.


Infraorder Scolecophidia
Scolecophidia
The Scolecophidia are an infraorder of snakes. They range in size from 10-100 cm in length, but may only be as small as 2 mm. All are fossorial. Currently, 3 families and 12 genera are recognized.-Families:-See also:...

3 families
Family Taxon author Genera Species Common name Geographic range
Anomalepidae Taylor
Edward Harrison Taylor
Edward Harrison Taylor was an American herpetologist from Kansas.He was born in Maysville, Missouri and studied at the University of Kansas in Lawrence, Kansas, graduating with a B.A. in 1912. Subsequently, he went to the Philippines, where at first he held a teacher's post in a village in central...

, 1939
4 15 Primitive blind snakes From southern Central America to northwestern South America. Disjunct populations in northeastern and southeastern South America.
Leptotyphlopidae
Leptotyphlopidae
The Leptotyphlopidae are a family of snakes found in North and South America, Africa, and Asia. All are fossorial and adapted to burrowing, feeding on ants and termites...

Stejneger
Leonhard Hess Stejneger
Leonhard Hess Stejneger was a Norwegian-born American ornithologist, herpetologist and zoologist. Stejneger specialized in vertebrate natural history studies. He gained his greatest reputation with reptiles and amphibians....

, 1892
2 87 Slender blind snakes Africa, western Asia from Turkey to northwestern India, on Socotra Island, from the southwestern United States south through Mexico and Central to South America, though not in the high Andes
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...

. In Pacific South America they occur as far south as southern coastal Peru, and on the Atlantic side as far as Uruguay and Argentina. In the Caribbean they are found on the Bahamas, Hispaniola
Hispaniola
Hispaniola is a major island in the Caribbean, containing the two sovereign states of the Dominican Republic and Haiti. The island is located between the islands of Cuba to the west and Puerto Rico to the east, within the hurricane belt...

 and the Lesser Antilles
Lesser Antilles
The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...

.
Typhlopidae
Typhlopidae
The Typhlopidae are a family of blind snakes. They are found mostly in the tropical regions of Africa, Asia, the Americas, and all mainland Australia and various islands. The rostral scale overhangs the mouth to form a shovel like burrowing structure. They live underground in burrows, and since...

Merrem
Blasius Merrem
Blasius Merrem was a German naturalist.Merrem was born at Bremen, and studied at the university of Göttingen under Johann Friedrich Blumenbach. He developed an interest in zoology, particularly ornithology...

, 1820
6 203 Typical blind snakes Most tropical and many subtropical regions around the world, particularly in Africa, Madagascar, Asia, islands in the Pacific, tropical America and in southeastern Europe.

Biology

Skeleton

The skeleton
Snake skeleton
A snake skeleton consists primarily of the skull, vertebrae, and ribs, with only vestigial remnants of the limbs.-Skull:The skull of a snake is a very complex structure, with numerous joints to allow the snake to swallow prey far larger than its head....

 of most snakes consists solely of the skull, hyoid, vertebral column, and ribs, though henophidian snakes retain vestiges of the pelvis and rear limbs. The skull of the snake consists of a solid and complete braincase, to which many of the other bones are only loosely attached, particularly the highly mobile jaw bones, which facilitate manipulation and ingestion of large prey items. The left and right sides of the lower jaw are joined only by a flexible ligament at the anterior tips, allowing them to separate widely, while the posterior end of the lower jaw bones articulate with a quadrate bone, allowing further mobility. The bones of the mandible and quadrate bones can also pick up ground borne vibrations. Because the sides of the jaw can move independently of one another, snakes resting their jaws on a surface have sensitive stereo hearing which can detect the position of prey. The jaw-quadrate-stapes pathway is capable of detecting vibrations on the angstrom
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....

 scale, despite the absence of an outer ear and the ossicle mechanism of impedance matching
Impedance matching
In electronics, impedance matching is the practice of designing the input impedance of an electrical load to maximize the power transfer and/or minimize reflections from the load....

 used in other vertebrates to receive vibrations from the air. The hyoid is a small bone located posterior and ventral to the skull, in the 'neck' region, which serves as an attachment for muscles of the snake's tongue, as it does in all other tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...

s.

The vertebral column consists of anywhere between 200 to 400 (or more) vertebrae. Tail vertebrae are comparatively few in number (often less than 20% of the total) and lack ribs, while body vertebrae each have two ribs articulating with them. The vertebrae have projections that allow for strong muscle attachment enabling locomotion without limbs. Autotomy
Autotomy
Autotomy or self amputation is the act whereby an animal severs one or more of its own appendages, usually as a self-defense mechanism designed to elude a predator's grasp...

 of the tail, a feature found in some lizards is absent in most snakes. Caudal autotomy in snakes is rare and is intervertebral, unlike that in lizards, which is intravertebral—that is, the break happens along a predefined fracture plane present on a vertebra.

In some snakes, most notably boas and pythons, there are vestiges of the hindlimbs in the form of a pair of pelvic spurs. These small, claw-like protrusions on each side of the cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...

 are the external portion of the vestigial hindlimb skeleton, which includes the remains of an ilium and femur.

Internal organs

The snake's heart is encased in a sac, called the pericardium
Pericardium
The pericardium is a double-walled sac that contains the heart and the roots of the great vessels.-Layers:...

, located at the bifurcation of the bronchi. The heart is able to move around, however, owing to the lack of a diaphragm. This adjustment protects the heart from potential damage when large ingested prey is passed through the esophagus. The spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...

 is attached to the gall bladder and pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...

 and filters the blood. The thymus gland is located in fatty tissue above the heart and is responsible for the generation of immune cells in the blood. The cardiovascular system of snakes is also unique for the presence of a renal portal system in which the blood from the snake's tail passes through the kidneys before returning to the heart.

The vestigial left lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

 is often small or sometimes even absent, as snakes' tubular bodies require all of their organs to be long and thin. In the majority of species, only one lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

 is functional. This lung contains a vascularized anterior portion and a posterior portion that does not function in gas exchange. This 'saccular lung' is used for hydrostatic purposes to adjust buoyancy in some aquatic snakes and its function remains unknown in terrestrial species. Many organs that are paired, such as kidneys or reproductive organs, are staggered within the body, with one located ahead of the other.

Snakes have no lymph node
Lymph node
A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...

s.

Moulting

Molting serves a number of functions. Firstly, the old and worn skin is replaced; secondly, it helps get rid of parasites such as mites and ticks. Renewal of the skin by moult
Moult
In biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...

ing is supposed to allow growth in some animals such as insects; however, this has been disputed in the case of snakes.
Molting occurs periodically throughout a snake's life. Before a molt, the snake stops eating and often hides or moves to a safe place. Just before shedding, the skin becomes dull and dry looking and the eyes become cloudy or blue-colored. The inner surface of the old skin liquefies. This causes the old skin to separate from the new skin beneath it. After a few days, the eyes clear and the snake "crawls" out of its old skin. The old skin breaks near the mouth and the snake wriggles out, aided by rubbing against rough surfaces. In many cases, the cast skin peels backward over the body from head to tail in one piece, like pulling a sock off inside-out. A new, larger, brighter layer of skin has formed underneath.

An older snake may shed its skin only once or twice a year. But a younger snake, still growing, may shed up to four times a year. The discarded skin gives a perfect imprint of the scale pattern, and it is usually possible to identify the snake if the discarded skin is reasonably intact. This periodic renewal has led to the snake being a symbol of healing
Healing
Physiological healing is the restoration of damaged living tissue, organs and biological system to normal function. It is the process by which the cells in the body regenerate and repair to reduce the size of a damaged or necrotic area....

 and medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

, as pictured in the Rod of Asclepius
Rod of Asclepius
The rod of Asclepius , also known as the asklepian, is an ancient symbol associated with astrology, the Greek god Asclepius, and with medicine and healing. It consists of a serpent entwined around a staff. The name of the symbol derives from its early and widespread association with Asclepius, the...

.
Vibration sensitivity
The part of the body in direct contact with the ground is very sensitive to vibration; thus, a snake can sense other animals approaching by detecting faint vibrations in the air and on the ground.

Infrared sensitivity
Pit vipers, pythons, and some boas have infrared-sensitive receptors
Infrared sensing in snakes
The ability to sense infrared thermal radiation evolved independently in several different families of snakes. Essentially, it allows these animals to “see” radiant heat at wavelengths between 5 and 30 μm to a degree of accuracy such that a blind rattlesnake can target vulnerable body parts of the...

 in deep grooves between the nostril and eye, although some have labial pits on their upper lip just below the nostrils (common in pythons), which allow them to "see" the radiated heat of warm-blooded prey mammals.


Venom

Cobras, vipers, and closely related species use venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

 to immobilize or kill their prey. The venom is modified saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...

, delivered through fangs
Snake venom
Snake venom is highly modified saliva that is produced by special glands of certain species of snakes. The glands which secrete the zootoxin are a modification of the parotid salivary gland of other vertebrates, and are usually situated on each side of the head below and behind the eye,...

. The fangs of 'advanced' venomous snakes like viperids and elapids are hollow to inject venom more effectively, while the fangs of rear-fanged snakes such as the boomslang merely have a groove on the posterior edge to channel venom into the wound. Snake venoms are often prey specific—their role in self-defense is secondary.

Venom, like all salivary secretions, is a predigestant that initiates the breakdown of food into soluble compounds, facilitating proper digestion. Even nonvenomous snake bites (like any animal bite) will cause tissue damage.

Certain birds, mammals, and other snakes (such as kingsnake
Kingsnake
Kingsnakes are a type of colubrid snake that are members of the Lampropeltis genus, which also includes the milk snake along with another four species and 45 sub-species....

s) that prey on venomous snakes have developed resistance and even immunity to certain venoms. Venomous snakes include three families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of snakes, and do not constitute a formal classification group used in taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

.

The term poisonous snake is mostly incorrect. Poison is inhaled or ingested, whereas venom is injected. There are, however, two exceptions: Rhabdophis
Rhabdophis
Rhabdophis is a genus of snakes, generally called keelback snakes, found primarily in southeast Asia.- Species of Rhabdophis :* Rhabdophis adleri* Rhabdophis angeli* Rhabdophis auriculata...

sequesters toxins from the toads it eats, then secretes them from nuchal glands to ward off predators, and a small population of garter snakes in Oregon retains enough toxin in their liver from the newts they eat to be effectively poisonous to small local predators (such as crows and foxes).

Snake venoms are complex mixtures of protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s, and are stored in poison glands at the back of the head. In all venomous snakes, these glands open through ducts into grooved or hollow teeth in the upper jaw. These proteins can potentially be a mix of neurotoxin
Neurotoxin
A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...

s (which attack the nervous system), hemotoxin
Hemotoxin
Hemotoxins, haemotoxins or hematotoxins are toxins that destroy red blood cells , disrupt blood clotting, and/or cause organ degeneration and generalized tissue damage. The term hemotoxin is to some degree a misnomer since toxins that damage the blood also damage other tissues...

s (which attack the circulatory system), cytotoxins, bungarotoxin
Bungarotoxin
α-Bungarotoxin is one of the components of the venom of the elapid snake Taiwanese banded krait . It binds irreversibly and competitively to the acetylcholine receptor found at the neuromuscular junction, causing paralysis, respiratory failure and death in the victim...

s and many other toxins that affect the body in different ways. Almost all snake venom contains hyaluronidase
Hyaluronidase
The hyaluronidases are a family of enzymes that degrade hyaluronic acid.In humans, there are six associated genes, including HYAL1, HYAL2, HYAL3, and PH-20/SPAM1.-Use as a drug:...

, an enzyme that ensures rapid diffusion of the venom.

Venomous snakes that use hemotoxins usually have fangs in the front of their mouths, making it easier for them to inject the venom into their victims. Some snakes that use neurotoxins (such as the mangrove snake
Boiga dendrophila
The gold-ringed cat snake or mangrove snake is a species of rear-fanged colubrid. It is one of the biggest cat snake species, averaging 6-8 feet in length...

) have fangs in the back of their mouths, with the fangs curled backwards. This makes it both difficult for the snake to use its venom and for scientists to milk them. Elapids, however, such as cobra
Cobra
Cobra is a venomous snake belonging to the family Elapidae. However, not all snakes commonly referred to as cobras are of the same genus, or even of the same family. The name is short for cobra capo or capa Snake, which is Portuguese for "snake with hood", or "hood-snake"...

s and kraits are proteroglyphous—they possess hollow fangs that cannot be erected toward the front of their mouths, and cannot "stab" like a viper. They must actually bite the victim.

It has recently been suggested that all snakes may be venomous to a certain degree, with harmless snakes having weak venom and no fangs. Most snakes currently labelled “nonvenomous” would still be considered harmless according to this theory, as they either lack a venom delivery method or are incapable of delivering enough to endanger a human. This theory postulates that snakes may have evolved from a common lizard ancestor that was venomous—and that venomous lizards like the gila monster
Gila monster
The Gila monster is a species of venomous lizard native to the southwestern United States and northwestern Mexican state of Sonora...

, beaded lizard
Beaded lizard
The Beaded lizard is a species of venomous lizard found principally in Mexico and southern Guatemala. Along with its congener, the Gila monster , it is the only lizard to have evolved an overt venom delivery system, and has long been considered the only venomous lizard...

, monitor lizards, and the now-extinct mosasaurs may also have derived. They share this venom clade with various other sauria
Sauria
Sauria is a clade of reptiles that includes all living diapsids, as well as their common ancestor and all its extinct descendants. The ancestral saurian was probably a small lizard-like creature living in the Permian Period...

n species.

Venomous snakes are classified in two taxonomic
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

:
  • Elapids – cobra
    Cobra
    Cobra is a venomous snake belonging to the family Elapidae. However, not all snakes commonly referred to as cobras are of the same genus, or even of the same family. The name is short for cobra capo or capa Snake, which is Portuguese for "snake with hood", or "hood-snake"...

    s including king cobras
    King Cobra
    The king cobra is the world's longest venomous snake, with a length up to 5.6 m . This species, which preys chiefly on other snakes, is found predominantly in forests from India through Southeast Asia to the Philippines and Indonesia...

    , kraits
    Bungarus
    Bungarus, commonly referred to as kraits , is a genus of venomous elapid snakes found in South and South-East Asia. There are 12 species and 5 subspecies recognized.- Distribution :...

    , mamba
    Mamba
    Mambas, of the genus Dendroaspis , are a group of highly venomous, fast-moving land-dwelling snakes of Africa. They belong to the family of Elapidae which includes cobras, coral snakes, taipans, brown snakes, tiger snakes, death adders, kraits and, debatably, sea snakes...

    s, Australian copperheads
    Austrelaps
    Austrelaps is a genus of venomous elapid snakes native to the relatively fertile temperate southern and eastern part of the Australian continent. Three species are currently recognized, of which there are no subspecies. They are commonly called copperheads or Australian copperheads...

    , sea snakes, and coral snake
    Coral snake
    The coral snakes are a large group of elapid snakes that can be subdivided into two distinct groups, Old World coral snakes and New World coral snakes...

    s.
  • Viperids
    Viperidae
    The Viperidae are a family of venomous snakes found all over the world, except in Antarctica, Australia, Ireland, Madagascar, Hawaii, various other isolated islands, and above the Arctic Circle. All have relatively long, hinged fangs that permit deep penetration and injection of venom. Four...

     – vipers
    Viperidae
    The Viperidae are a family of venomous snakes found all over the world, except in Antarctica, Australia, Ireland, Madagascar, Hawaii, various other isolated islands, and above the Arctic Circle. All have relatively long, hinged fangs that permit deep penetration and injection of venom. Four...

    , rattlesnake
    Rattlesnake
    Rattlesnakes are a group of venomous snakes of the genera Crotalus and Sistrurus of the subfamily Crotalinae . There are 32 known species of rattlesnake, with between 65-70 subspecies, all native to the Americas, ranging from southern Alberta and southern British Columbia in Canada to Central...

    s, copperheads
    Agkistrodon contortrix
    Agkistrodon contortrix is a species of venomous snake found in North America, a member of the Crotalinae subfamily. The more common name for the species is "copperhead". The behavior of Agkistrodon contortrix may lead to accidental encounters with humans...

    /cottonmouths
    Agkistrodon piscivorus
    Agkistrodon piscivorus is a venomous snake, a species of pit viper, found in the southeastern United States. Adults are large and capable of delivering a painful and potentially fatal bite. When antagonized they will stand their ground by coiling their bodies and displaying their fangs...

    , and bushmasters
    Lachesis (genus)
    Lachesis is a genus of venomous pitvipers found in remote forested areas of Central and South America. The generic name refers to one of the Three Fates in Greek mythology who determined the length of the thread of life...

    .


There is a third family containing the opistoglyphous (rear-fanged) snakes (as well as the majority of other snake species):
  • Colubrid
    Colubrid
    A colubrid is a member of the snake family Colubridae. This broad classification of snakes includes about two-thirds of all snake species on earth. The earliest species of the snake family date back to the Oligocene epoch. With 304 genera and 1,938 species, Colubridae is the largest snake family...

    s – boomslang
    Boomslang
    The boomslang is a large venomous colubrid snake.-Taxonomy & etymology:It is currently the only species in its genus, although several species and subspecies have been described in the past...

    s, tree snakes, vine snakes
    Ahaetulla
    Ahaetulla is a genus of colubrid snakes commonly referred to as vine snakes, or whip snakes. They are mildly venomous and what is commonly termed as 'rear-fanged' or more appropriately, opisthoglyphous, meaning their enlarged teeth or fangs intended to aid in venom delivery are located in the back...

    , mangrove snakes
    Boiga
    Boiga is a large genus of mildly venomous, rear-fanged, colubrid snakes typically known as the cat-eyed snakes or just cat snakes. They are primarily found throughout southeast Asia, India and Australia, but due to their extremely hardy nature and adaptability have spread to many other suitable...

    , although not all colubrid
    Colubrid
    A colubrid is a member of the snake family Colubridae. This broad classification of snakes includes about two-thirds of all snake species on earth. The earliest species of the snake family date back to the Oligocene epoch. With 304 genera and 1,938 species, Colubridae is the largest snake family...

    s are venomous.

Feeding and diet

All snakes are strictly carnivorous
Hypercarnivore
A hypercarnivore is an animal which has a diet that is more than 70% meat, with the balance consisting of non-animal foods such as fungi, fruits or other plant material. Some examples include the big cats, dolphins, eagles, snakes, marlin, most sharks, and such invertebrates as octopuses and sea...

, eating small animals including lizards, other snakes, small mammals, birds, eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

, fish, snails or insects. Because snakes cannot bite or tear their food to pieces, they must swallow prey whole. The body size of a snake has a major influence on its eating habits. Smaller snakes eat smaller prey. Juvenile pythons might start out feeding on lizards or mice and graduate to small deer or antelope as an adult, for example.

The snake's jaw
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...

 is a complex structure. Contrary to the popular belief that snakes can dislocate their jaws, snakes have a very flexible lower jaw
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...

, the two halves of which are not rigidly attached, and numerous other joints in their skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...

 (see snake skull), allowing them to open their mouths wide enough to swallow their prey whole, even if it is larger in diameter than the snake itself. For example, the African egg-eating snake
Dasypeltis
Dasypeltis is a genus of colubrid snakes. It is one of only two taxonomic groups of snakes known to have adapted to feed exclusively on eggs...

 has flexible jaws adapted for eating eggs much larger than the diameter of its head. This snake has no teeth, but does have bony protrusions on the inside edge of its spine
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

, which it uses to break shells when it eats eggs.

While the majority of snakes eat a variety of prey animals, there is some specialization by some species. King cobra
King Cobra
The king cobra is the world's longest venomous snake, with a length up to 5.6 m . This species, which preys chiefly on other snakes, is found predominantly in forests from India through Southeast Asia to the Philippines and Indonesia...

s and the Australian bandy-bandy consume other snakes. Pareas iwesakii and other snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...

-eating colubrid
Colubrid
A colubrid is a member of the snake family Colubridae. This broad classification of snakes includes about two-thirds of all snake species on earth. The earliest species of the snake family date back to the Oligocene epoch. With 304 genera and 1,938 species, Colubridae is the largest snake family...

s of subfamily Pareatinae
Pareatinae
Pareatinae is a small subfamily of the Colubridae family of snakes. It encompasses a mere 3 genera, which include snakes that eat snails....

 have more teeth on the right side of their mouths than on the left, as the shells of their prey usually spiral clockwise

Some snakes have a venomous bite, which they use to kill their prey before eating it. Other snakes kill their prey by constriction
Constriction
Constriction is a method used by various snake species to kill their prey. Although some species of venomous and mildly-venomous snakes do use constriction to subdue their prey, most snakes which use constriction lack venom. The snake initially strikes at its prey and holds on, pulling the prey...

. Still others swallow their prey whole and alive.

After eating, snakes become dormant while the process of digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

 takes place. Digestion is an intense activity, especially after consumption of large prey. In species that feed only sporadically, the entire intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...

 enters a reduced state between meals to conserve energy. The digestive system is then 'up-regulated' to full capacity within 48 hours of prey consumption. Being ectothermic (“cold-blooded”), the surrounding temperature plays a large role in snake digestion. The ideal temperature for snakes to digest is 30 °C (86 °F). So much metabolic
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 energy is involved in a snake's digestion that in the Mexican rattlesnake (Crotalus durissus
Crotalus durissus
Crotalus durissus is a venomous pitviper species found in South America. The most widely distributed member of its genus, this species poses a serious medical problem in many parts of its range...

), surface body temperature increases by as much as 1.2 C-change during the digestive process. Because of this, a snake disturbed after having eaten recently will often regurgitate
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...

 its prey to be able to escape the perceived threat. When undisturbed, the digestive process is highly efficient, with the snake's digestive enzymes dissolving and absorbing everything but the prey's hair
Hair
Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....

 (or feather
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...

s) and claws, which are excreted along with waste
Uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates such as ammonium acid urate. Uric acid is created when the body breaks down purine nucleotides. High blood concentrations of uric acid...

.

Locomotion

The lack of limbs does not impede the movement of snakes. They have developed several different modes of locomotion to deal with particular environments. Unlike the gaits of limbed animals, which form a continuum, each mode of snake locomotion is discrete and distinct from the others; transitions between modes are abrupt.

Lateral undulation

Lateral undulation is the sole mode of aquatic locomotion, and the most common mode of terrestrial locomotion. In this mode, the body of the snake alternately flexes to the left and right, resulting in a series of rearward-moving "waves." While this movement appears rapid, snakes have rarely been documented moving faster than two body-lengths per second, often much less. This mode of movement has the same net cost of transport (calories burned per meter moved) as running in lizards of the same mass.
Terrestrial

Terrestrial lateral undulation is the most common mode of terrestrial locomotion for most snake species. In this mode, the posteriorly moving waves push against contact points in the environment, such as rocks, twigs, irregularities in the soil, etc. Each of these environmental objects, in turn, generates a reaction force directed forward and towards the midline of the snake, resulting in forward thrust while the lateral components cancel out. The speed of this movement depends upon the density of push-points in the environment, with a medium density of about 8 along the snake's length being ideal. The wave speed is precisely the same as the snake speed, and as a result, every point on the snake's body follows the path of the point ahead of it, allowing snakes to move through very dense vegetation and small openings.
Aquatic


When swimming, the waves become larger as they move down the snake's body, and the wave travels backwards faster than the snake moves forwards. Thrust is generated by pushing their body against the water, resulting in the observed slip. In spite of overall similarities, studies show that the pattern of muscle activation is different in aquatic versus terrestrial lateral undulation, which justifies calling them separate modes. All snakes can laterally undulate forward (with backward-moving waves), but only sea snakes have been observed reversing the motion (moving backwards with forward-moving waves).

Sidewinding

Most often employed by colubroid snakes (colubrids, elapids, and vipers
Viperidae
The Viperidae are a family of venomous snakes found all over the world, except in Antarctica, Australia, Ireland, Madagascar, Hawaii, various other isolated islands, and above the Arctic Circle. All have relatively long, hinged fangs that permit deep penetration and injection of venom. Four...

) when the snake must move in an environment that lacks irregularities to push against (rendering lateral undulation impossible), such as a slick mud flat, or a sand dune. Sidewinding is a modified form of lateral undulation in which all of the body segments oriented in one direction remain in contact with the ground, while the other segments are lifted up, resulting in a peculiar "rolling" motion. This mode of locomotion overcomes the slippery nature of sand or mud by pushing off with only static portions on the body, thereby minimizing slipping. The static nature of the contact points can be shown from the tracks of a sidewinding snake, which show each belly scale imprint, without any smearing. This mode of locomotion has very low caloric cost, less than ⅓ of the cost for a lizard or snake to move the same distance. Contrary to popular belief, there is no evidence that sidewinding is associated with the sand being hot.



Concertina

When push-points are absent, but there is not enough space to use sidewinding because of lateral constraints, such as in tunnels, snakes rely on concertina locomotion. In this mode, the snake braces the posterior portion of its body against the tunnel wall while the front of the snake extends and straightens. The front portion then flexes and forms an anchor point, and the posterior is straightened and pulled forwards. This mode of locomotion is slow and very demanding, up to seven times the cost of laterally undulating over the same distance. This high cost is due to the repeated stops and starts of portions of the body as well as the necessity of using active muscular effort to brace against the tunnel walls.

Rectilinear

The slowest mode of snake locomotion is rectilinear locomotion, which is also the only one where the snake does not need to bend its body laterally, though it may do so when turning. In this mode, the belly scales are lifted and pulled forward before being placed down and the body pulled over them. Waves of movement and stasis pass posteriorly, resulting in a series of ripples in the skin. The ribs of the snake do not move in this mode of locomotion and this method is most often used by large pythons, boas, and viper
Viperidae
The Viperidae are a family of venomous snakes found all over the world, except in Antarctica, Australia, Ireland, Madagascar, Hawaii, various other isolated islands, and above the Arctic Circle. All have relatively long, hinged fangs that permit deep penetration and injection of venom. Four...

s when stalking prey across open ground as the snake's movements are subtle and harder to detect by their prey in this manner.

Other

The movement of snakes in arboreal habitats has only recently been studied. While on tree branches, snakes use several modes of locomotion depending on species and bark texture. In general, snakes will use a modified form of concertina locomotion on smooth branches, but will laterally undulate if contact points are available. Snakes move faster on small branches and when contact points are present, in contrast to limbed animals, which do better on large branches with little 'clutter'.

Gliding snakes (Chrysopelea
Chrysopelea
Chrysopelea, or more commonly known as the flying snake, is a genus that belongs to the family Colubridae. Flying snakes are mildly venomous, though they are considered harmless because their toxicity is not dangerous to humans...

) of Southeast Asia launch themselves from branch tips, spreading their ribs and laterally undulating as they glide between trees. These snakes can perform a controlled glide for hundreds of feet depending upon launch altitude and can even turn in midair.

Reproduction

Although a wide range of reproductive modes are used by snakes, all snakes employ internal fertilization
Internal fertilization
In mammals, internal fertilization is done through copulation, which involves the insertion of the penis into the vagina. Some other higher vertebrate animals reproduce internally, but their fertilization is cloacal.The union of spermatozoa of the parent organism. At some point, the growing egg or...

. This is accomplished by means of paired, forked hemipenes
Hemipenis
A hemipenis is one of a pair of intromittent organs of male squamates .Hemipenes are usually held inverted, within the body, and are everted for reproduction via erectile tissue, much like that in the human penis. Only one is used at a time, and some evidence indicates males alternate use between...

, which are stored, inverted, in the male's tail. The hemipenes are often grooved, hooked, or spined in order to grip the walls of the female's cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...

.

Most species of snakes lay eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

, but most snakes abandon the eggs shortly after laying. However, a few species (such as the King cobra
King Cobra
The king cobra is the world's longest venomous snake, with a length up to 5.6 m . This species, which preys chiefly on other snakes, is found predominantly in forests from India through Southeast Asia to the Philippines and Indonesia...

) actually construct nests and stay in the vicinity of the hatchlings after incubation. Most pythons coil around their egg-clutches and remain with them until they hatch. A female python will not leave the eggs, except to occasionally bask in the sun or drink water. She will even “shiver” to generate heat to incubate the eggs.

Some species of snake are ovoviviparous
Ovoviviparity
Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animals in which embryos develop inside eggs that are retained within the mother's body until they are ready to hatch...

 and retain the eggs within their bodies until they are almost ready to hatch. Recently, it has been confirmed that several species of snake are fully viviparous
Vivipary
Vivipary has two different meanings. In animals, it means development of the embryo inside the body of the mother, eventually leading to live birth, as opposed to laying eggs...

, such as the boa constrictor
Boa constrictor
The Boa constrictor is a large, heavy-bodied species of snake. It is a member of the family Boidae found in North, Central, and South America, as well as some islands in the Caribbean. A staple of private collections and public displays, its color pattern is highly variable yet distinctive...

 and green anaconda, nourishing their young through a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

 as well as a yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...

, which is highly unusual among reptiles, or anything else outside of placental mammals. Retention of eggs and live birth are most often associated with colder environments, as the retention of the young within the female
Female
Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...

.

Interactions with humans

Bite

Snakes do not ordinarily prey on humans, and most will not attack humans unless the snake is startled or injured, preferring instead to avoid contact. With the exception of large constrictors, nonvenomous snakes are not a threat to humans. The bite of nonvenomous snakes is usually harmless because their teeth are designed for grabbing and holding, rather than tearing or inflicting a deep puncture wound. Although the possibility of an infection and tissue damage is present in the bite of a nonvenomous snake, venomous snakes present far greater hazard to humans.

Documented deaths resulting from snake bites are uncommon. Nonfatal bites from venomous snakes may result in the need for amputation of a limb or part thereof. Of the roughly 725 species of venomous snakes worldwide, only 250 are able to kill a human with one bite. Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 averages only one fatal snake bite per year. In India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, 250,000 snakebites are recorded in a single year, with as many as 50,000 recorded initial deaths.

The treatment for a snakebite is as variable as the bite itself. The most common and effective method is through antivenom (or antivenin), a serum made from the venom of the snake. Some antivenom is species specific (monovalent) while some is made for use with multiple species in mind (polyvalent). In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 for example, all species of venomous snakes are pit vipers, with the exception of the coral snake
Coral snake
The coral snakes are a large group of elapid snakes that can be subdivided into two distinct groups, Old World coral snakes and New World coral snakes...

. To produce antivenom, a mixture of the venoms of the different species of rattlesnake
Rattlesnake
Rattlesnakes are a group of venomous snakes of the genera Crotalus and Sistrurus of the subfamily Crotalinae . There are 32 known species of rattlesnake, with between 65-70 subspecies, all native to the Americas, ranging from southern Alberta and southern British Columbia in Canada to Central...

s, copperheads, and cottonmouths is injected into the body of a horse in ever-increasing dosages until the horse is immunized. Blood is then extracted from the immunized horse; the serum is separated and further purified and freeze-dried. It is reconstituted with sterile water and becomes antivenom. For this reason, people who are allergic to horses are more likely to suffer an allergic reaction to antivenom. Antivenom for the more dangerous species (such as mamba
Mamba
Mambas, of the genus Dendroaspis , are a group of highly venomous, fast-moving land-dwelling snakes of Africa. They belong to the family of Elapidae which includes cobras, coral snakes, taipans, brown snakes, tiger snakes, death adders, kraits and, debatably, sea snakes...

s, taipan
Taipan
The taipans are a genus of large, fast, highly venomous Australasian snakes of the elapid family.-Overview:The taipan was named by Donald Thomson after the word used by the Wik-Mungkan Aboriginal people of central Cape York Peninsula, Queensland, Australia.There are three known species: the coastal...

s, and cobra
Cobra
Cobra is a venomous snake belonging to the family Elapidae. However, not all snakes commonly referred to as cobras are of the same genus, or even of the same family. The name is short for cobra capo or capa Snake, which is Portuguese for "snake with hood", or "hood-snake"...

s) is made in a similar manner in India, South Africa, and Australia, although these antivenoms are species-specific.

Snake charmers

In some parts of the world, especially in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, snake charming
Snake charming
Snake charming is the practice of pretending to hypnotise a snake by playing an instrument. A typical performance may also include handling the snakes or performing other seemingly dangerous acts, as well as other street performance staples, like juggling and sleight of hand...

 is a roadside show performed by a charmer. In such a show, the snake charmer carries a basket that contains a snake that he seemingly charms by playing tunes from his flutelike musical instrument, to which the snake responds. Snakes lack external ears, though they do have internal ears, and respond to the movement of the flute, not the actual noise.

The Wildlife Protection Act of 1972
Wildlife Protection Act of 1972
The Wildlife Protection Act of 1972 refers to a sweeping package of legislation enacted in 1972 by the Government of India. Before 1972, India only had five designated national parks...

 in India technically proscribes snake charming on grounds of reducing animal cruelty. Other snake charmers also have a snake and mongoose
Mongoose
Mongoose are a family of 33 living species of small carnivorans from southern Eurasia and mainland Africa. Four additional species from Madagascar in the subfamily Galidiinae, which were previously classified in this family, are also referred to as "mongooses" or "mongoose-like"...

 show, where both the animals have a mock fight; however, this is not very common, as the snakes, as well as the mongooses, may be seriously injured or killed. Snake charming as a profession is dying out in India because of competition from modern forms of entertainment and environment laws proscribing the practice.

Trapping

The Irulas tribe of Andhra Pradesh
Andhra Pradesh
Andhra Pradesh , is one of the 28 states of India, situated on the southeastern coast of India. It is India's fourth largest state by area and fifth largest by population. Its capital and largest city by population is Hyderabad.The total GDP of Andhra Pradesh is $100 billion and is ranked third...

 and Tamil Nadu
Tamil Nadu
Tamil Nadu is one of the 28 states of India. Its capital and largest city is Chennai. Tamil Nadu lies in the southernmost part of the Indian Peninsula and is bordered by the union territory of Pondicherry, and the states of Kerala, Karnataka, and Andhra Pradesh...

 in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 have been hunter-gatherers in the hot, dry plains forests, and have practiced the art of snake catching for generations. They have a vast knowledge of snakes in the field. They generally catch the snakes with the help of a simple stick. Earlier, the Irulas caught thousands of snakes for the snake-skin industry. After the complete ban of the snake-skin industry in India and protection of all snakes under the Indian Wildlife (Protection) Act 1972
Wildlife Protection Act of 1972
The Wildlife Protection Act of 1972 refers to a sweeping package of legislation enacted in 1972 by the Government of India. Before 1972, India only had five designated national parks...

, they formed the Irula Snake Catcher's Cooperative and switched to catching snakes for removal of venom, releasing them in the wild after four extractions. The venom so collected is used for producing life-saving antivenom, biomedical research and for other medicinal products. The Irulas are also known to eat some of the snakes they catch and are very useful in rat extermination in the villages.

Despite the existence of snake charmers, there have also been professional snake catchers or wranglers. Modern-day snake trapping involves a herpetologist using a long stick with a V- shaped end. Some television show hosts, like Bill Haast
Bill Haast
William E. "Bill" Haast was the director of the Miami Serpentarium Laboratories, a facility near Punta Gorda, Florida, which produces snake venom for medical and research use. Haast extracted venom from venomous snakes from the time he was a boy...

, Austin Stevens
Austin Stevens
Austin James Stevens is a South African-born herpetologist and wildlife photographer best known for hosting a series of snake documentaries. Austin is also the author of 2 books.-Biography:...

, Steve Irwin
Steve Irwin
Stephen Robert "Steve" Irwin , nicknamed "The Crocodile Hunter", was an Australian television personality, wildlife expert, and conservationist. Irwin achieved worldwide fame from the television series The Crocodile Hunter, an internationally broadcast wildlife documentary series which he co-hosted...

, and Jeff Corwin
Jeff Corwin
Jeffrey Scott Corwin is an American animal and nature conservationist, best known as host and executive producer of Animal Planet cable channel television programs, The Jeff Corwin Experience and Corwin's Quest.-Early years:...

, prefer to catch them using bare hands.

Consumption

While not commonly thought of as food in most cultures, in some cultures, the consumption of snakes is acceptable, or even considered a delicacy, prized for its alleged pharmaceutical effect of warming the heart. Snake soup of Cantonese cuisine
Cantonese cuisine
Cantonese cuisine comes from Guangdong Province in southern China and is one of 8 superdivisions of Chinese cuisine. Its prominence outside China is due to the great numbers of early emigrants from Guangdong. Cantonese chefs are highly sought after throughout the country...

 is consumed by local people in autumn
Autumn
Autumn is one of the four temperate seasons. Autumn marks the transition from summer into winter usually in September or March when the arrival of night becomes noticeably earlier....

, to warm up their body. Western cultures document the consumption of snakes under extreme circumstances of hunger. Cooked rattlesnake
Rattlesnake
Rattlesnakes are a group of venomous snakes of the genera Crotalus and Sistrurus of the subfamily Crotalinae . There are 32 known species of rattlesnake, with between 65-70 subspecies, all native to the Americas, ranging from southern Alberta and southern British Columbia in Canada to Central...

 meat is an exception, which is commonly consumed in parts of the Midwestern United States. In Asian countries such as China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

, Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...

, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...

, Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...

 and Cambodia
Cambodia
Cambodia , officially known as the Kingdom of Cambodia, is a country located in the southern portion of the Indochina Peninsula in Southeast Asia...

, drinking the blood of snakes—particularly the cobra
Cobra
Cobra is a venomous snake belonging to the family Elapidae. However, not all snakes commonly referred to as cobras are of the same genus, or even of the same family. The name is short for cobra capo or capa Snake, which is Portuguese for "snake with hood", or "hood-snake"...

—is believed to increase sexual virility. The blood is drained while the cobra is still alive when possible, and is usually mixed with some form of liquor to improve the taste.

In some Asian countries, the use of snakes in alcohol is also accepted. In such cases, the body of a snake or several snakes is left to steep in a jar or container of liquor. It is claimed that this makes the liquor stronger (as well as more expensive). One example of this is the Habu
Trimeresurus flavoviridis
Trimeresurus flavoviridis is a venomous pitviper species found in Japan in the Ryukyu Islands. No subspecies are currently recognized.-Description:...

 snake sometimes placed in the Okinawan liquor Awamori
Awamori
Awamori is an alcoholic beverage indigenous to and unique to Okinawa, Japan. It is made from rice, and is not a direct product of brewing but of distillation ....

 also known as "Habu Sake."

U.S. Army Special Forces trainees are taught to catch, kill, and eat snakes during their survival course; this has earned them the nickname "snake eaters," which the video game Metal Gear Solid 3: Snake Eater
Metal Gear Solid 3: Snake Eater
is an award-winning stealth action video game directed by Hideo Kojima. Snake Eater was developed by Konami Computer Entertainment Japan and published by Konami for the PlayStation 2, and was released on November 17, 2004 in North America; December 16, 2004 in Japan; March 4, 2005 in Europe; and on...

 may be inferred to draw from.

Snake wine
Snake Wine
Snake wine is an alcoholic beverage produced by infusing whole snakes in rice wine or grain alcohol. The drink was first recorded to have been consumed in China during the Western Zhou dynasty and considered an important curative and believed to reinvigorate a person according to Traditional...

 (蛇酒) is an alcoholic beverage produced by infusing whole snakes in rice wine or grain alcohol. The drink was first recorded to have been consumed in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 during the Western Zhou dynasty and considered an important curative and believed to reinvigorate a person according to Traditional Chinese medicine
Traditional Chinese medicine
Traditional Chinese Medicine refers to a broad range of medicine practices sharing common theoretical concepts which have been developed in China and are based on a tradition of more than 2,000 years, including various forms of herbal medicine, acupuncture, massage , exercise , and dietary therapy...

.

Pets

In the Western world, some snakes (especially docile species such as the ball python and corn snake
Corn Snake
The Corn Snake , or Red Rat Snake, is a North American species of Rat Snake that subdues its small prey by constriction. The name "Corn Snake" is a holdover from the days when southern farmers stored harvested ears of corn in a wood frame or log building called a crib...

) are kept as pets. To meet this demand a captive breeding
Herpetoculture
Herpetoculture is the keeping of live reptiles and amphibians in captivity, whether as a hobby or as a commercial breeding operation. "Herps" is an informal term that refers to both reptiles and amphibians...

 industry has developed. Snakes bred in captivity tend to make better pets and are considered preferable to wild caught specimens. Snakes can be very low maintenance pets, especially compared to more traditional species. They require minimal space, as most common species do not exceed five feet in length. Pet snakes can be fed relatively infrequently, usually once every 5–14 days. Certain snakes have a lifespan of more than 40 years if given proper care.

Symbolism

In Egyptian history
History of Egypt
Egyptian history can be roughly divided into the following periods:*Prehistoric Egypt*Ancient Egypt**Early Dynastic Period of Egypt: 31st to 27th centuries BC**Old Kingdom of Egypt: 27th to 22nd centuries BC...

, the snake occupies a primary role with the Nile cobra adorning the crown of the pharaoh in ancient times. It was worshipped
Snake worship
The worship of serpent deities is present in several old cultures, particularly in religion and mythology, where snakes were seen as entities of strength and renewal.-Hindu mythology:...

 as one of the gods and was also used for sinister purposes: murder of an adversary and ritual suicide (Cleopatra
Cleopatra VII of Egypt
Cleopatra VII Philopator was the last pharaoh of Ancient Egypt.She was a member of the Ptolemaic dynasty, a family of Greek origin that ruled Egypt after Alexander the Great's death during the Hellenistic period...

).

In Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

 snakes are often associated with deadly and dangerous antagonists, but this is not to say that snakes are symbolic of evil; in fact, snakes are a chthonic
Chthonic
Chthonic designates, or pertains to, deities or spirits of the underworld, especially in relation to Greek religion. The Greek word khthon is one of several for "earth"; it typically refers to the interior of the soil, rather than the living surface of the land or the land as territory...

 symbol, roughly translated as 'earthbound'. The nine-headed Lernaean Hydra
Lernaean Hydra
In Greek mythology, the Lernaean Hydra was an ancient nameless serpent-like chthonic water beast, with reptilian traits, that possessed many heads — the poets mention more heads than the vase-painters could paint, and for each head cut off it grew two more — and poisonous breath so virulent even...

 that Hercules
Hercules
Hercules is the Roman name for Greek demigod Heracles, son of Zeus , and the mortal Alcmene...

 defeated and the three Gorgon
Gorgon
In Greek mythology, the Gorgon was a terrifying female creature. The name derives from the Greek word gorgós, which means "dreadful." While descriptions of Gorgons vary across Greek literature, the term commonly refers to any of three sisters who had hair of living, venomous snakes, and a...

 sisters are children of Gaia, the earth. Medusa
Medusa
In Greek mythology Medusa , " guardian, protectress") was a Gorgon, a chthonic monster, and a daughter of Phorcys and Ceto. The author Hyginus, interposes a generation and gives Medusa another chthonic pair as parents. Gazing directly upon her would turn onlookers to stone...

 was one of the three Gorgon sisters who Perseus
Perseus
Perseus ,Perseos and Perseas are not used in English. the legendary founder of Mycenae and of the Perseid dynasty of Danaans there, was the first of the mythic heroes of Greek mythology whose exploits in defeating various archaic monsters provided the founding myths of the Twelve Olympians...

 defeated. Medusa is described as a hideous mortal, with snakes instead of hair and the power to turn men to stone with her gaze. After killing her, Perseus gave her head to Athena
Athena
In Greek mythology, Athena, Athenê, or Athene , also referred to as Pallas Athena/Athene , is the goddess of wisdom, courage, inspiration, civilization, warfare, strength, strategy, the arts, crafts, justice, and skill. Minerva, Athena's Roman incarnation, embodies similar attributes. Athena is...

 who fixed it to her shield called the Aegis
Aegis
An aegis is a large collar or cape worn in ancient times to display the protection provided by a high religious authority or the holder of a protective shield signifying the same, such as a bag-like garment that contained a shield. Sometimes the garment and the shield are merged, with a small...

. The Titans
Titan (mythology)
In Greek mythology, the Titans were a race of powerful deities, descendants of Gaia and Uranus, that ruled during the legendary Golden Age....

 are also depicted in art with snakes instead of legs and feet for the same reason—they are children of Gaia and Ouranos (Uranus), so they are bound to the earth.
The legendary account of the foundation of Thebes
Ancient Thebes (Boeotia)
See Thebes, Greece for the modern city built on the ancient ruins.Ancient Thebes was a Boeotian city-state , situated to the north of the Cithaeron range, which divides Boeotia from Attica, and on the southern edge of the Boeotian plain...

 mentioned a monster snake
guarding the spring from which the new settlement was to draw its water. In fighting and killing the snake, the companions of the founder Cadmus
Cadmus
Cadmus or Kadmos , in Greek mythology was a Phoenician prince, the son of king Agenor and queen Telephassa of Tyre and the brother of Phoenix, Cilix and Europa. He was originally sent by his royal parents to seek out and escort his sister Europa back to Tyre after she was abducted from the shores...

 all perished - leading to the term "Cadmean victory
Cadmean victory
A Cadmean victory is a reference to a victory involving one's own ruin, from Cadmus , the legendary founder of Thebes in Boeotia and the mythic bringer of the alphabet to Greece. On seeking to establish the city, Cadmus required water from a spring guarded by a monster snake. He sent his...

" (i.e. a victory
Victory
Victory is successful conclusion of a fight or competition..Victory may refer to:**strategic victory**tactical victory** Pyrrhic victory, a victory at heavy cost to the victorious party**Victory columns**Victory Monuments**Victory personified...

 involving one's own ruin).

Three medical symbols involving snakes that are still used today are Bowl of Hygieia
Bowl of Hygieia
Bowl of Hygieia is one of the symbols of pharmacy. Hygieia was the Greek goddess of health.- Usage of symbol by pharmaceutical associations :...

, symbolizing pharmacy, and the Caduceus
Caduceus
The caduceus is the staff carried by Hermes in Greek mythology. The same staff was also borne by heralds in general, for example by Iris, the messenger of Hera. It is a short staff entwined by two serpents, sometimes surmounted by wings...

 and Rod of Asclepius
Rod of Asclepius
The rod of Asclepius , also known as the asklepian, is an ancient symbol associated with astrology, the Greek god Asclepius, and with medicine and healing. It consists of a serpent entwined around a staff. The name of the symbol derives from its early and widespread association with Asclepius, the...

, which are symbols denoting medicine in general.

India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 is often called the land of snakes and is steeped in tradition regarding snakes. Snakes are worshipped as gods even today with many women pouring milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

 on snake pits (despite snakes' aversion for milk). The cobra is seen on the neck of Shiva
Shiva
Shiva is a major Hindu deity, and is the destroyer god or transformer among the Trimurti, the Hindu Trinity of the primary aspects of the divine. God Shiva is a yogi who has notice of everything that happens in the world and is the main aspect of life. Yet one with great power lives a life of a...

 and Vishnu
Vishnu
Vishnu is the Supreme god in the Vaishnavite tradition of Hinduism. Smarta followers of Adi Shankara, among others, venerate Vishnu as one of the five primary forms of God....

 is depicted often as sleeping on a seven-headed snake or within the coils of a serpent. There are also several temples in India solely for cobras sometimes called Nagraj (King of Snakes) and it is believed that snakes are symbols of fertility. There is a Hindu festival called Nag Panchami
Nag panchami
Nāg Panchamī is a festival during which religious Hindus in some parts of India worship either images of or live Nāgas on the fifth day after Amavasya of the month of Shraavana. Traditionally, married young women visit their premarital households to celebrate the festival...

 each year on which day snakes are venerated and prayed to. See also Nāga
Naga
Naga or NAGA may refer to:* Nāga, a group of serpent deities in Hindu and Buddhist mythology.-People:* Nayan / Nayar/Nair people of Kerala Society* Naga people, a diverse ethnic identity in Northeast India...

.

In India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 there is another mythology about snakes. Commonly known in Hindi
Hindi
Standard Hindi, or more precisely Modern Standard Hindi, also known as Manak Hindi , High Hindi, Nagari Hindi, and Literary Hindi, is a standardized and sanskritized register of the Hindustani language derived from the Khariboli dialect of Delhi...

 as "Ichchhadhari" snakes. Such snakes can take the form of any living creature, but prefer human form. These mythical snakes possess a valuable gem called "Mani", which is more brilliant than diamond. There are many stories in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 about greedy people trying to possess this gem and ending up getting killed.

The Ouroboros
Ouroboros
The Ouroboros is an ancient symbol depicting a serpent or dragon eating its own tail. The name originates from within Greek language; οὐρά meaning "tail" and βόρος meaning "eating", thus "he who eats the tail"....

 is a symbol associated with many different religions and customs, and is claimed to be related to Alchemy
Alchemy
Alchemy is an influential philosophical tradition whose early practitioners’ claims to profound powers were known from antiquity. The defining objectives of alchemy are varied; these include the creation of the fabled philosopher's stone possessing powers including the capability of turning base...

. The Ouroboros or Oroboros is a snake eating its own tail in a clock-wise direction (from the head to the tail) in the shape of a circle, representing manifestation of one's own life and rebirth, leading to immortality.

The snake
Snake (zodiac)
The Snake is one of the 12-year cycle of animals which appear in the Chinese zodiac related to the Chinese calendar. The Year of the Snake is associated with the earthly branch symbol 巳.-Years and the Five Elements:...

 is one of the 12 celestial animals of Chinese Zodiac
Chinese zodiac
The Shēngxiào , better known in English as the Chinese Zodiac, is a scheme that relates each year to an animal and its reputed attributes, according to a 12-year mathematical cycle...

, in the Chinese calendar
Chinese calendar
The Chinese calendar is a lunisolar calendar, incorporating elements of a lunar calendar with those of a solar calendar. It is not exclusive to China, but followed by many other Asian cultures as well...

.

Many ancient Peruvian cultures worshipped nature. They emphasized animals and often depicted snakes in their art.

Religion

Snakes are a part of Hindu worship. A festival Nag Panchami
Nag panchami
Nāg Panchamī is a festival during which religious Hindus in some parts of India worship either images of or live Nāgas on the fifth day after Amavasya of the month of Shraavana. Traditionally, married young women visit their premarital households to celebrate the festival...

 is celebrated every year on snakes. Most images of Lord Shiva
Shiva
Shiva is a major Hindu deity, and is the destroyer god or transformer among the Trimurti, the Hindu Trinity of the primary aspects of the divine. God Shiva is a yogi who has notice of everything that happens in the world and is the main aspect of life. Yet one with great power lives a life of a...

 depict snake around his neck. Puranas have various stories associated with Snakes. In the Puranas, Shesha
Shesha
In Hindu tradition, Shesha or Sheshanaag is the king of all nagas, one of the primal beings of creation, and according to the Bhagavata Purana, an Avatar of the Supreme God known as Sankarshan. In the Puranas, Shesha is said to hold all the planets of the Universe on his hoods and to constantly...

 is said to hold all the planets of the Universe on his hoods and to constantly sing the glories of Vishnu from all his mouths. He is sometimes referred to as "Ananta-Shesha," which means "Endless Shesha." Other notable snakes in Hinduism are Ananta
Ananta
Ananta is a Sanskrit word meaning "without end".It may refer to:*Ananta , one of the names of Vishnu.*Ananta , Actor and Producer for Bengali film.*Ananta, a serpent on which Vishnu lies, aka Shesha....

, Vasuki
Vasuki
Vasuki is a Sanskrit name for a naga, one of the serpents of Buddhist and Hindu mythology. He is a great King of the nagas and has a gem on his head. Manasa, another naga, is his sister...

, Taxak, Karkotaka
Karkotaka
Karkotaka was a naga king, who bit Nala at the request of Indra, transforming Nala into a twisted and ugly shape. Karkotaka had deceived Narada who cursed him due to which he could not move a step...

 and Pingala
Pingala
Pingala is the traditional name of the author of the ' , the earliest known Sanskrit treatise on prosody.Nothing is known about Piṅgala himself...

. The term Nāga
Naga
Naga or NAGA may refer to:* Nāga, a group of serpent deities in Hindu and Buddhist mythology.-People:* Nayan / Nayar/Nair people of Kerala Society* Naga people, a diverse ethnic identity in Northeast India...

 is used to refer to entities that take the form of large snakes in Hinduism
Hinduism
Hinduism is the predominant and indigenous religious tradition of the Indian Subcontinent. Hinduism is known to its followers as , amongst many other expressions...

 and Buddhism
Buddhism
Buddhism is a religion and philosophy encompassing a variety of traditions, beliefs and practices, largely based on teachings attributed to Siddhartha Gautama, commonly known as the Buddha . The Buddha lived and taught in the northeastern Indian subcontinent some time between the 6th and 4th...

.

Snakes have also been widely revered, such as in ancient Greece
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

, where the serpent was seen as a healer, and Asclepius
Asclepius
Asclepius is the God of Medicine and Healing in ancient Greek religion. Asclepius represents the healing aspect of the medical arts; his daughters are Hygieia , Iaso , Aceso , Aglæa/Ægle , and Panacea...

 carried two intertwined on his wand, a symbol seen today on many ambulances.

In religious terms, the snake is arguably the most important animal in ancient Mesoamerica
Mesoamerica
Mesoamerica is a region and culture area in the Americas, extending approximately from central Mexico to Belize, Guatemala, El Salvador, Honduras, Nicaragua, and Costa Rica, within which a number of pre-Columbian societies flourished before the Spanish colonization of the Americas in the 15th and...

. “In states of ecstasy, lords dance a serpent dance; great descending snakes adorn and support buildings from Chichen Itza
Chichen Itza
Chichen Itza is a large pre-Columbian archaeological site built by the Maya civilization located in the northern center of the Yucatán Peninsula, in the Municipality of Tinúm, Yucatán state, present-day Mexico....

 to Tenochtitlan, and the Nahuatl
Nahuatl
Nahuatl is thought to mean "a good, clear sound" This language name has several spellings, among them náhuatl , Naoatl, Nauatl, Nahuatl, Nawatl. In a back formation from the name of the language, the ethnic group of Nahuatl speakers are called Nahua...

 word coatl meaning serpent or twin, forms part of primary deities such as Mixcoatl
Mixcoatl
Mixcoatl , or Camaxtli, was the god of the hunt and identified with the Milky Way, the stars, and the heavens in several Mesoamerican cultures. He was the patron deity of the Otomi, the Chichimecs, and several groups that claimed descent from the Chichimecs...

, Quetzalcoatl
Quetzalcoatl
Quetzalcoatl is a Mesoamerican deity whose name comes from the Nahuatl language and has the meaning of "feathered serpent". The worship of a feathered serpent deity is first documented in Teotihuacan in the first century BCE or first century CE...

, and Coatlicue
Coatlicue
Coatlicue, also known as Teteoinan , "The Mother of Gods" , is the Aztec goddess who gave birth to the moon, stars, and Huitzilopochtli, the god of the sun and war...

.” In both Maya
Maya calendar
The Maya calendar is a system of calendars and almanacs used in the Maya civilization of pre-Columbian Mesoamerica, and in many modern Maya communities in highland Guatemala. and in Chiapas....

 and Aztec
Aztec
The Aztec people were certain ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl language and who dominated large parts of Mesoamerica in the 14th, 15th and 16th centuries, a period referred to as the late post-classic period in Mesoamerican chronology.Aztec is the...

 calendars, the fifth day of the week was known as Snake Day.

In Judaism
Judaism
Judaism ) is the "religion, philosophy, and way of life" of the Jewish people...

, the snake of brass is also a symbol of healing, of one's life being saved from imminent death (Book of Numbers
Book of Numbers
The Book of Numbers is the fourth book of the Hebrew Bible, and the fourth of five books of the Jewish Torah/Pentateuch....

 21:6–9).

In Christianity
Christianity
Christianity is a monotheistic religion based on the life and teachings of Jesus as presented in canonical gospels and other New Testament writings...

, Christ
Christ
Christ is the English term for the Greek meaning "the anointed one". It is a translation of the Hebrew , usually transliterated into English as Messiah or Mashiach...

's redemptive work is compared to saving one's life through beholding the Nehushtan
Nehushtan
The Nehushtan , in the Hebrew Bible, was a sacred object in the form of a snake of brass upon a pole.The priestly source of the Torah says that Moses used a 'fiery serpent' to cure the Israelites from snakebites...

 (serpent of brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...

) (Gospel of John
Gospel of John
The Gospel According to John , commonly referred to as the Gospel of John or simply John, and often referred to in New Testament scholarship as the Fourth Gospel, is an account of the public ministry of Jesus...

 3:14). Snake handlers
Snake handling
Snake handling or serpent handling is a religious ritual in a small number of Pentecostal churches in the U.S., usually characterized as rural and Holiness. The practice began in the early 20th century in Appalachia, spreading to mostly coal mining towns. The practice plays only a small part of...

 use snakes as an integral part of church worship in order to exhibit their faith in divine protection. However, more commonly in Christianity, the serpent has been seen as a representative of evil
Evil
Evil is the violation of, or intent to violate, some moral code. Evil is usually seen as the dualistic opposite of good. Definitions of evil vary along with analysis of its root motive causes, however general actions commonly considered evil include: conscious and deliberate wrongdoing,...

 and sly plotting, which can be seen in the description in Genesis chapter 3 of a snake in the Garden of Eden
Garden of Eden
The Garden of Eden is in the Bible's Book of Genesis as being the place where the first man, Adam, and his wife, Eve, lived after they were created by God. Literally, the Bible speaks about a garden in Eden...

 tempting Eve
Eve
Eve is the first woman created by God in the Book of Genesis.Eve may also refer to:-People:*Eve , a common given name and surname*Eve , American recording artist and actress-Places:...

. Saint Patrick
Saint Patrick
Saint Patrick was a Romano-Briton and Christian missionary, who is the most generally recognized patron saint of Ireland or the Apostle of Ireland, although Brigid of Kildare and Colmcille are also formally patron saints....

 is reputed to have expelled all snakes from Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

 while Christianising the country in the 5th century, thus explaining the absence of snakes there.

In Christianity
Christianity
Christianity is a monotheistic religion based on the life and teachings of Jesus as presented in canonical gospels and other New Testament writings...

 and Judaism
Judaism
Judaism ) is the "religion, philosophy, and way of life" of the Jewish people...

, the snake makes its infamous appearance in the first book (Genesis 3:1) of the Bible
Bible
The Bible refers to any one of the collections of the primary religious texts of Judaism and Christianity. There is no common version of the Bible, as the individual books , their contents and their order vary among denominations...

 when a serpent appears before the first couple Adam and Eve
Adam and Eve
Adam and Eve were, according to the Genesis creation narratives, the first human couple to inhabit Earth, created by YHWH, the God of the ancient Hebrews...

 and tempts them with the forbidden fruit
Forbidden fruit
Forbidden fruit is any object of desire whose appeal is a direct result of knowledge that cannot or should not be obtained or something that someone may want but is forbidden to have....

 from the Tree of Knowledge
Tree of Knowledge of Good and Evil
In the Book of Genesis, the tree of the knowledge of good and evil or the tree of knowledge was a tree in the middle of the Garden of Eden. . God directly forbade Adam to eat the fruit of this tree...

. The snake returns in Exodus when Moses
Moses
Moses was, according to the Hebrew Bible and Qur'an, a religious leader, lawgiver and prophet, to whom the authorship of the Torah is traditionally attributed...

, as a sign of God's power, turns his staff into a snake and when Moses made the Nehushtan
Nehushtan
The Nehushtan , in the Hebrew Bible, was a sacred object in the form of a snake of brass upon a pole.The priestly source of the Torah says that Moses used a 'fiery serpent' to cure the Israelites from snakebites...

, a bronze snake on a pole that when looked at cured the people of bites from the snakes that plagued them in the desert. The serpent makes its final appearance symbolizing Satan
Satan
Satan , "the opposer", is the title of various entities, both human and divine, who challenge the faith of humans in the Hebrew Bible...

 in the Book of Revelation
Book of Revelation
The Book of Revelation is the final book of the New Testament. The title came into usage from the first word of the book in Koine Greek: apokalupsis, meaning "unveiling" or "revelation"...

: "And he laid hold on the dragon the old serpent, which is the devil and Satan
Satan
Satan , "the opposer", is the title of various entities, both human and divine, who challenge the faith of humans in the Hebrew Bible...

, and bound him for a thousand years." (Revelation 20:2)

In Neo-Paganism and Wicca
Wicca
Wicca , is a modern Pagan religious movement. Developing in England in the first half of the 20th century, Wicca was popularised in the 1950s and early 1960s by a Wiccan High Priest named Gerald Gardner, who at the time called it the "witch cult" and "witchcraft," and its adherents "the Wica."...

, the snake is seen as a symbol
Symbol
A symbol is something which represents an idea, a physical entity or a process but is distinct from it. The purpose of a symbol is to communicate meaning. For example, a red octagon may be a symbol for "STOP". On a map, a picture of a tent might represent a campsite. Numerals are symbols for...

 of wisdom
Wisdom
Wisdom is a deep understanding and realization of people, things, events or situations, resulting in the ability to apply perceptions, judgements and actions in keeping with this understanding. It often requires control of one's emotional reactions so that universal principles, reason and...

 and knowledge
Knowledge
Knowledge is a familiarity with someone or something unknown, which can include information, facts, descriptions, or skills acquired through experience or education. It can refer to the theoretical or practical understanding of a subject...

.

See also

  • Legend of the White Snake
  • Limbless vertebrates
    Limbless vertebrates
    Many vertebrates have evolved limbless forms. Reptiles have on a number of occasions evolved into limbless forms - snakes, amphisbaenia, and legless lizards...

  • List of Serpentes families
  • List of snakes
  • Ophiology
    Ophiology
    Ophiology is a branch of herpetology, the study of reptiles and amphibians, and deals with the scientific study of snakes, including the natural history and behavior of the animals. An individual who studies snakes is known as an ophiologist...

  • Snake skeleton
    Snake skeleton
    A snake skeleton consists primarily of the skull, vertebrae, and ribs, with only vestigial remnants of the limbs.-Skull:The skull of a snake is a very complex structure, with numerous joints to allow the snake to swallow prey far larger than its head....

  • The New Encyclopedia of Snakes
    The New Encyclopedia of Snakes
    The New Encyclopedia of Snakes is an encyclopedia by Chris Mattison.-Book summary:The encyclopedia has information about snakes that is listed from A-Z...

  • Venomous snake
    Venomous snake
    "Poisonous snake" redirects here. For true poisonous snakes, see Rhabdophis.Venomous snakes are snakes which have venom glands and specialized teeth for the injection of venom...

  • Cadmean Victory
    Cadmean victory
    A Cadmean victory is a reference to a victory involving one's own ruin, from Cadmus , the legendary founder of Thebes in Boeotia and the mythic bringer of the alphabet to Greece. On seeking to establish the city, Cadmus required water from a spring guarded by a monster snake. He sent his...


External links

(INDIA)
  • BBC Nature: Snake news, and video clips from BBC programmes past and present.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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