Earthworm
Overview
Earthworm is the common name for the largest members of Oligochaeta
Oligochaeta
Oligochaeta is a subclass of animals in the biological phylum Annelida, which is made up of many types of aquatic and terrestrial worms, and this includes all of the various earthworms...

 (which is either a class or subclass depending on the author) in the phylum Annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...

a. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female. Theoretical cladistic
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...

 studies have placed them instead in the suborder Lumbricina of the order Haplotaxida, but this may again soon change.
Encyclopedia
Earthworm is the common name for the largest members of Oligochaeta
Oligochaeta
Oligochaeta is a subclass of animals in the biological phylum Annelida, which is made up of many types of aquatic and terrestrial worms, and this includes all of the various earthworms...

 (which is either a class or subclass depending on the author) in the phylum Annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...

a. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female. Theoretical cladistic
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...

 studies have placed them instead in the suborder Lumbricina of the order Haplotaxida, but this may again soon change. Folk names for the earthworm include "dew-worm", "Rainworm", "night crawler" and "angleworm" (due to its use as fishing bait
Fishing bait
Fishing bait is any substance used to attract and catch fish, e.g. on the end of a fishing hook, or inside a fish trap. Traditionally, nightcrawlers, insects, and smaller bait fish have been used for this purpose...

).

Earthworms are also called megadriles (or big worms), as opposed to the microdriles (or small worms) in the families Tubificidae
Tubificidae
The Naididae are a family of clitellate oligochaete worms like the sludge worm, Tubifex tubifex. They are key components of the benthic communities of many freshwater and marine ecosystems....

, Lumbriculidae
Lumbriculidae
The Lumbriculidae are a family of microdrile oligochaetes common in fresh-water environments, including streams, lakes, marshes, wells and ground-water. They should not be confused with the earthworm family Lumbricidae. Many species and even genera are highly endemic, mainly in Siberia and the...

, and Enchytraeidae
Enchytraeidae
The Enchytraeidae are a microdrile oligochaete family. They resemble small earthworms and include both terrestrial species known as potworms that live in highly organic terrestrial environments, as well as some that are marine...

, among others. The megadriles are characterized by having a distinct clitellum
Clitellum
The clitellum is a thickened glandular section of the body wall in earthworms and leeches, that secretes a viscid sac in which the eggs are deposited...

 (which is much more obvious than the single-layered one of the microdriles) and a vascular system with true capillaries.

Anatomy

The basic body plan
Body plan
A body plan is the blueprint for the way the body of an organism is laid out. An organism's symmetry, its number of body segments and number of limbs are all aspects of its body plan...

 of an earthworm is a tube, the digestive system, within a tube, the muscular slimy, moist outer body. The body is annular, formed of segments that are most specialized in the anterior. Earthworms have a simple closed circulatory system. They have two main blood vessels that extend through the length of their body: a ventral blood vessel which leads the blood to the posterior end, and a dorsal blood vessel which leads to the anterior end. The dorsal vessel is contractile and pumps blood forward, where it is pumped into the ventral vessel by a series of "hearts" (aortic arches) which vary in number in the different taxa. The blood is distributed from the ventral vessel into capillaries on the body wall and other organs and into a vascular sinus in the gut wall, where gases and nutrients are exchanged. This arrangement may be complicated in the various groups by suboesophageal, supraoesophageal, parietal and neural vessels, but the basic arrangement holds in all earthworms. Most earthworms are decomposers feeding on undecayed leaf and other plant matter, others are more geophagous
Geophagy
Geophagy is the practice of eating earthy or soil-like substances such as clay, and chalk. It exists in animals in the wild and also in humans, most often in rural or preindustrial societies among children and pregnant women...

.

Reproduction

Earthworms are hermaphrodite
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...

s: They typically have two pairs of testes, surrounded by 2 pairs of testes sacs. There are 2 or 4 pairs of seminal vesicles which produce, store and release the sperm via the male pores, and ovaries and ovipores in segment 13 that release eggs via female pores on segment 14. However, most also have one or more pairs of spermatheca
Spermatheca
The spermatheca , also called receptaculum seminis , is an organ of the female reproductive tract in insects, some molluscs, oligochaeta worms and certain other invertebrates and vertebrates...

e (depending on the species) that are internal sacs which receive and store sperm from the other worm in copulation. Some species use external spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...

s for transfer instead.

Copulation and reproduction are separate processes in earthworms. The mating pair overlap front ends ventrally and each exchanges sperm with the other. The clitellum
Clitellum
The clitellum is a thickened glandular section of the body wall in earthworms and leeches, that secretes a viscid sac in which the eggs are deposited...

 becomes very reddish to pinkish in color. The cocoon, or egg case, is secreted by the clitellum band which is near the front of the worm, but behind the spermathecae. Some time after copulation, long after the worms have separated, the clitellum secretes the cocoon which forms a ring around the worm. The worm then backs out of the ring, and as it does so, injects its own eggs and the other worm's sperm into it. As the worm slips out, the ends of the cocoon seal to form a vaguely lemon-shaped incubator (cocoon) in which the embryonic worms develop. They emerge as small, but fully formed earthworms, except for a lack of the sex structures, which develop later in about 60 to 90 days. They attain full size in about one year, sometimes sooner. Scientists predict that the average lifespan under field conditions is 4–8 years, still most garden varieties live only one to two years. Several common earthworm species are mostly parthenogenetic
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...

, that is, with asexual reproduction resulting in clones.

Digestion

There is a digestion system in an earthworm. The process of nutrition begins in the mouth, where food is sucked in by a muscular pharynx. From there, food goes down the esophagus through peristalsis (visceral muscle contractions.) After this, the food is stored in the crop, which retains food and has the ability to expand. From there food goes into the gizzard where sand and muscular contractions churn the food and increase the surface area. At this point food enters the intestine which has the ability to absorb food, then food exits through the anus. A rectum is unnecessary because an earthworm is in a moist environment and thus does not require water reclamation.

Regeneration

Earthworms have the ability to regenerate lost segments, but this ability varies between species and depends on the extent of the damage. Stephenson (1930) devoted a chapter of his monograph to this topic, while G.E. Gates spent 20 years studying regeneration in a variety of species, but “because little interest was shown”, Gates (1972) only published a few of his findings that, nevertheless, show it is theoretically possible to grow two whole worms from a bisected specimen in certain species. Gates’s reports included:
  • Eisenia fetida
    Eisenia fetida
    Eisenia fetida , known under various common names such as redworm, brandling worm, tiger worm and red wiggler worm, red californian earth worm, is a species of earthworm adapted to decaying organic material. These worms thrive in rotting vegetation, compost, and manure; they are epigeal...

    (Savigny, 1826) with head regeneration, in an anterior direction, possible at each intersegmental level back to and including 23/24, while tails were regenerated at any levels behind 20/21.
  • Lumbricus terrestris Linnaeus, 1758 replacing anterior segments from as far back as 13/14 and 16/17 but tail regeneration was never found.
  • Perionyx excavatus Perrier, 1872 readily regenerated lost parts of the body, in an anterior direction from as far back as 17/18, and in a posterior direction as far forward as 20/21.
  • Lampito mauritii Kinberg, 1867 with regeneration in anterior direction at all levels back to 25/26 and tail regeneration from 30/31; head regeneration was sometimes believed to be caused by internal amputation resulting from Sarcophaga
    Sarcophaga
    Sarcophaga is a genus of true flies, the type of the flesh-fly family .This genus occurs essentially worldwide. These flies are generally well-sized and of a greyish color; like many of their relatives, the typical patterns are lengthwise darker stripes on the thorax and dark and light square dots...

    sp. larval infestation.
  • Criodrilus lacuum Hoffmeister, 1845 also has prodigious regenerative capacity with ‘head’ regeneration from as far back as 40/41.
  • Lumbriculus veriega Able to split into two segments and survive.

An unidentified Tasmanian earthworm shown growing a second head is reported here:.

Rainstorms and "stranding" behaviour

Earthworms can sometimes be found on the surface of the ground following heavy rain storms, as a storm may flood the soil with excessive water. However, if the surface where they find themselves is unexpectedly paved, rocky, or compacted (hardened), they may become stranded, potentially suffering injury or death from causes such as heat, exposure, dehydration, or predation. Note, there are some earthworm species that can survive for several days in water if it is sufficiently oxygenated.

Earthworms may also come to the surface during rain in order to mate, and therefore, an alternative hypothesis concerning "stranding" behavior is that as some species (notably Lumbricus terrestris
Lumbricus terrestris
Lumbricus terrestris is a large reddish worm native to Europe, but now also widely distributed elsewhere around the world due to human introductions...

) come to the surface to mate they may become stranded.

Another hypothesis is that the worms may be using the moist conditions on the surface so they can breathe and to travel more quickly than they can underground, thus moving to and colonizing new areas more quickly. Since the relative humidity of the surface and air is higher during and after rain, they do not become dehydrated quite as rapidly. However, if true, this is a very risky behavior near dawn, in high summer, or in the daytime, since earthworms die quickly when exposed to direct sunlight with its high heat, light and strong UV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 content, and are more vulnerable to predators such as bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s.
A further hypothesis is that, because there are many other organisms beside the earthworm in the ground as well, and these organisms all tend to increase respiration as water content of the soil increases, carbon dioxide gas may dissolve into the rainwater forming a higher than usual acid content carbonic acid
Carbonic acid
Carbonic acid is the inorganic compound with the formula H2CO3 . It is also a name sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3. Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates...

 in the soil area. As the soil becomes too acidic for the worms, they seek a more neutral environment on the surface.

Locomotion and importance to soil

Earthworms travel underground by the means of waves of muscular contractions which alternately shorten and lengthen the body. The shortened part is anchored to the surrounding soil by tiny claw-like bristles (seta
Seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....

e) set along its segmented length. In all the body segments except the first, last and clitellum, there is a ring of S-shaped setae embedded in the epidermal pit of each segment (perichaetine). The whole burrowing process is aided by the secretion of lubricating mucus. Worms can make gurgling noises underground when disturbed as a result of the worm moving through its lubricated tunnels. They also work as biological "piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

s" forcing air through the tunnels as they move. Thus earthworm activity aerates and mixes the soil, and is constructive to mineralization and nutrient uptake by vegetation. Certain species of earthworm come to the surface and graze on the higher concentrations of organic matter present there, mixing it with the mineral soil. Because a high level of organic matter mixing is associated with soil fertility, an abundance of earthworms is beneficial to the organic gardener. In fact as long ago as 1881 Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...

 wrote: It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures.

Benefits

The major benefits of earthworm activities to soil fertility can be summarized as:
  • Biological. In many soils, earthworms play a major role in converting large pieces of organic matter (e.g. dead leaves) into rich humus, and thus improving soil fertility. This is achieved by the worm's actions of pulling down below any organic matter deposited on the dried dirt, such as leaf fall or manure, either for food or when it needs to plug its burrow. Once in the burrow, the worm will shred the leaf and partially digest it, then mingle it with the earth by saturating it with intestinal secretions. Worm casts (see below) can contain 40% more humus than the top 9" (23 cm) of soil in which the worm is living.

  • Chemical. As well as dead organic matter
    Organic matter
    Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds...

    , the earthworm also ingests any other soil particles that are small enough—including stones up to 1/20 of an inch (1.25mm) across—into its gizzard wherein minute fragments of grit grind everything into a fine paste which is then digested in the intestine. When the worm excretes this in the form of casts which are deposited on the surface or deeper in the soil, minerals and plant nutrients are made available in an accessible form. Investigations in the US
    United States
    The United States of America is a federal constitutional republic comprising fifty states and a federal district...

     show that fresh earthworm casts are 5 times richer in available nitrogen
    Nitrogen
    Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

    , 7 times richer in available phosphate
    Phosphate
    A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...

    s and 11 times richer in available potash
    Potash
    Potash is the common name for various mined and manufactured salts that contain potassium in water-soluble form. In some rare cases, potash can be formed with traces of organic materials such as plant remains, and this was the major historical source for it before the industrial era...

     than the surrounding upper 6 inches (150 mm) of soil. In conditions where there is plenty of available humus, the weight of casts produced may be greater than 4.5 kg (10 lb) per worm per year, in itself an indicator of why it pays the gardener or farmer to keep worm populations high.
  • Physical. By its burrowing actions, the earthworm is of great value in keeping the soil structure open, creating a multitude of channels which allow the processes of both aeration and drainage to occur. Permaculture
    Permaculture
    Permaculture is an approach to designing human settlements and agricultural systems that is modeled on the relationships found in nature. It is based on the ecology of how things interrelate rather than on the strictly biological concerns that form the foundation of modern agriculture...

     co-founder Bill Mollison
    Bill Mollison
    Bruce Charles 'Bill' Mollison is a researcher, author, scientist, teacher and naturalist. He is considered to be the 'father of permaculture', an integrated system of design, co-developed with David Holmgren, that encompasses not only agriculture, horticulture, architecture and ecology, but also...

     points out that by sliding in their tunnels, earthworms "act as an innumerable army of pistons pumping air in and out of the soils on a 24 hour cycle (more rapidly at night)". Thus the earthworm not only creates passages for air and water to traverse, but is itself a vital component in the living biosystem that is healthy soil. Earthworms continue to move through the soil due to the excretion of mucus into the soil that acts as a lubricant for easier movement of the worm. (See Bioturbation
    Bioturbation
    In oceanography, limnology, pedology, geology , and archaeology, bioturbation is the displacement and mixing of sediment particles and solutes by fauna or flora . The mediators of bioturbation are typically annelid worms , bivalves In oceanography, limnology, pedology, geology (especially...

    .)

The earthworm's existence cannot be taken for granted. Dr. W. E. Shewell Cooper
Shewell Cooper
Dr. Wilfred Edward Shewell-Cooper, M.B.E., N.D.H., F.L.S., F.R.S.L., F.R.H.S., Dip. Hort. was a British organic gardener and pioneer of no dig gardening. He was the author of Soil, Humus and Health , The Royal Gardeners , Grow your own food supply , The ABC of Vegetable Gardening and many other...

 observed "tremendous numerical differences between adjacent gardens" (Soil, Humus And Health), and worm populations are affected by a host of environmental factors, many of which can be influenced by good management practices on the part of the gardener or farmer.

Darwin estimated that arable land
Arable land
In geography and agriculture, arable land is land that can be used for growing crops. It includes all land under temporary crops , temporary meadows for mowing or pasture, land under market and kitchen gardens and land temporarily fallow...

 contains up to 53,000 worms per acre (13/m²), but more recent research from Rothamsted Experimental Station
Rothamsted Experimental Station
The Rothamsted Experimental Station, one of the oldest agricultural research institutions in the world, is located at Harpenden in Hertfordshire, England. It is now known as Rothamsted Research...

 has produced figures suggesting that even poor soil may support 250,000/acre (62/m²), whilst rich fertile farmland may have up to 1,750,000/acre (432/m²), meaning that the weight of earthworms beneath the farmer's soil could be greater than that of his livestock upon its surface.

Earthworms as invasive species

From a total of around 6,000 species, only about 120 species are widely distributed around the world. These are the peregrine or cosmopolitan earthworms.

Australia

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...

 has 650 known species of native earthworm that survive in both rich and in nutrient-poor conditions where they may be sensitive to changes in the environment. Introduced species are commonly found in agricultural environments along with persistent natives. Most of the 75 or so exotics have been accidentally introduced into Australia. The total species numbers are predicted to exceed 2,000.

North America

A total of approximately 182 earthworm taxa in 12 families are reported from America north of Mexico, i.e., USA & Canada, of which 60 (ca. 33%) are exotic/introduced. Only two genera of Lumbricid
Lumbricidae
The Lumbricidae is a family of earthworms which includes most of the earthworm species well known to Europeans. About 33 lumbricid species have become naturalized around the world, but the bulk of the species are in Holarctic: from Canada and the United States The Lumbricidae is a family of...

 earthworms are indigenous to North America while introduced genera have spread to areas where earthworms did not formerly exist, especially in the north where forest development relies on a large amount of undecayed leaf matter. When worms decompose that leaf layer, the ecology may shift making the habitat unsurvivable for certain species of trees, ferns and wildflowers. Another possible ecologic impact of greater earthworm numbers: larger earthworms (e.g. the night crawler, Lumbricus terrestris, and the Alabama jumper, Amynthas agrestis) can be eaten by adult salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...

s, and when the salamanders do consume the earthworms they are more successful at reproduction. However, those earthworms are too large for juvenile salamanders to consume, which leads to a net loss in salamander population.

Currently there is no economically feasible method for controlling invasive earthworms in forests. Earthworms normally spread slowly, but can be quickly introduced by human activities such as construction earthmoving, or by fishermen releasing bait, or by plantings.

United Kingdom

A recent threat to earthworm populations in the UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 is the New Zealand Flatworm
New Zealand flatworm
The New Zealand flatworm is a large flatworm native to New Zealand. It can vary from 5 mm in length when hatched to approximately in mature adults. The ventral surface of the flatworm is a pale buff colour while the dorsal surface is dark brown...

 (Artiposthia triangulata), which feeds upon the earthworm, but in the UK, has no natural predator itself. At present sightings of the New Zealand flatworm have been mainly localised, but this is no reason for complacency as it has spread extensively since its introduction in 1960 through contaminated soil and plant pots. Any sightings of the flatworm should be reported to the Scottish Crop Research Institute
Scottish Crop Research Institute
The Scottish Crop Research Institute more commonly known as the SCRI was a scientific institute located in Invergowrie near Dundee, Scotland. As of April 2011, when SCRI merged with the Macaulay Land Use Institute it is now part of The James Hutton Institute.-History:The institute was opened in...

, which is monitoring its spread.

Special habitats

While, as the name earthworm suggests, the main habitat of earthworms is in soil, the situation is more complicated than that. The brandling worm Eisenia fetida
Eisenia fetida
Eisenia fetida , known under various common names such as redworm, brandling worm, tiger worm and red wiggler worm, red californian earth worm, is a species of earthworm adapted to decaying organic material. These worms thrive in rotting vegetation, compost, and manure; they are epigeal...

lives in decaying plant matter and manure. Arctiostrotus vancouverensis from Vancouver Island
Vancouver Island
Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...

 and the Olympic Peninsula
Olympic Peninsula
The Olympic Peninsula is the large arm of land in western Washington state of the USA, that lies across Puget Sound from Seattle. It is bounded on the west by the Pacific Ocean, the north by the Strait of Juan de Fuca, and the east by Puget Sound. Cape Alava, the westernmost point in the contiguous...

 is generally found in decaying conifer logs. Aporrectodea limicola and Sparganophilus
Sparganophilus
Sparganophilus, the only genus in the family Sparganophilidae, is a group of long slender limicolous earthworms native to North America. There are an unknown number of species, most of them undescribed, throughout the continent and into Central America. One species, S...

and several others are found in mud in streams. Some species are arboreal. Even in the soil species, there are special habitats, such as soils derived from serpentine which have an earthworm fauna of their own.

Ecology

Earthworms are classified into three main ecophysiological categories: (1) leaf litter/compost dwelling worms (epigeic) e.g. Eisenia fetida; (2) topsoil or subsoil dwelling worms (endogeics); and (3) worms that construct permanent deep burrows through which they visit the surface to obtain plant material for food, such as leaves (anecic), e.g. Lumbricus terrestris.
Earthworm populations depend on both physical and chemical properties of the soil, such as soil temperature, moisture, pH, salts, aeration and texture, as well as available food, and the ability of the species to reproduce and disperse. One of the most important environmental factors is pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

, but earthworms vary in their preferences. Most earthworms favor neutral to slightly acidic soil. However, Lumbricus terrestris are still present in a pH of 5.4 and Dendrobaena octaedra at a pH of 4.3 and some Megascolecidae
Megascolecidae
Megascolecidae is a large family of earthworms which has native representatives in Australia, New Zealand, Southeast and East Asia, and North America. The most ancient lineages of the family show a Gondwanan distribution and have been used as evidence of continental drift. Members of the Pheretima...

 are present in extremely acid humic soils. Soil pH may also influence the numbers of worms that go into diapause
Diapause
Diapause is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions...

. The more acidic the soil, the sooner worms go into diapause, and remain in diapause the longest time at a pH of 6.4.

Earthworms form the base of many food chains. They are preyed upon by many species of bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s (e.g. starling
Starling
Starlings are small to medium-sized passerine birds in the family Sturnidae. The name "Sturnidae" comes from the Latin word for starling, sturnus. Many Asian species, particularly the larger ones, are called mynas, and many African species are known as glossy starlings because of their iridescent...

s, thrushes
Thrush (bird)
The thrushes, family Turdidae, are a group of passerine birds that occur worldwide.-Characteristics:Thrushes are plump, soft-plumaged, small to medium-sized birds, inhabiting wooded areas, and often feed on the ground or eat small fruit. The smallest thrush may be the Forest Rock-thrush, at and...

, gull
Gull
Gulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...

s, crow
Crow
Crows form the genus Corvus in the family Corvidae. Ranging in size from the relatively small pigeon-size jackdaws to the Common Raven of the Holarctic region and Thick-billed Raven of the highlands of Ethiopia, the 40 or so members of this genus occur on all temperate continents and several...

s, European Robin
European Robin
The European Robin , most commonly known in Anglophone Europe simply as the Robin, is a small insectivorous passerine bird that was formerly classed as a member of the thrush family , but is now considered to be an Old World flycatcher...

s and American Robin
American Robin
The American Robin or North American Robin is a migratory songbird of the thrush family. It is named after the European Robin because of its reddish-orange breast, though the two species are not closely related, with the European robin belonging to the flycatcher family...

s), snakes, mammals (e.g. bear
Bear
Bears are mammals of the family Ursidae. Bears are classified as caniforms, or doglike carnivorans, with the pinnipeds being their closest living relatives. Although there are only eight living species of bear, they are widespread, appearing in a wide variety of habitats throughout the Northern...

s, fox
Fox
Fox is a common name for many species of omnivorous mammals belonging to the Canidae family. Foxes are small to medium-sized canids , characterized by possessing a long narrow snout, and a bushy tail .Members of about 37 species are referred to as foxes, of which only 12 species actually belong to...

es, hedgehog
Hedgehog
A hedgehog is any of the spiny mammals of the subfamily Erinaceinae and the order Erinaceomorpha. There are 17 species of hedgehog in five genera, found through parts of Europe, Asia, Africa, and New Zealand . There are no hedgehogs native to Australia, and no living species native to the Americas...

s, moles
Mole (animal)
Moles are small cylindrical mammals adapted to a subterranean lifestyle. They have velvety fur; tiny or invisible ears and eyes; and short, powerful limbs with large paws oriented for digging. The term is especially and most properly used for the true moles, those of the Talpidae family in the...

) and invertebrates (e.g. ground beetle
Ground beetle
Ground beetles are a large, cosmopolitan family of beetles, Carabidae, with more than 40,000 species worldwide, approximately 2,000 of which are found in North America and 2,700 in Europe.-Description and ecology:...

s and other beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...

s, 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...

s, slug
Slug
Slug is a common name that is normally applied to any gastropod mollusc that lacks a shell, has a very reduced shell, or has a small internal shell...

s). Earthworms have many internal parasites including Protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...

, Platyhelminthes, Nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

s; they can be found in the worms' blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

, seminal vesicles, coelom
Coelom
The coelom is a fluid-filled cavity formed within the mesoderm. Coeloms developed in triploblasts but were subsequently lost in several lineages. Loss of coelom is correlated with reduction in body size...

, 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...

, or in the cocoons.

The application of chemical fertilizers, sprays and dusts can have a disastrous effect on earthworm populations. Nitrogenous fertilizers tend to create acidic conditions
Soil pH
The soil pH is a measure of the acidity or basicity in soils. pH is defined as the negative logarithm of the activity of hydrogen ions in solution. It ranges from 0 to 14, with 7 being neutral. A pH below 7 is acidic and above 7 is basic. Soil pH is considered a master variable in soils as it...

, which are fatal to the worms, and often dead specimens are to be found on the surface following the application of substances like DDT
DDT
DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history....

, lime sulphur and lead arsenate. 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...

, changes in farming practices such as the application of superphosphates on pasture
Pasture
Pasture is land used for grazing. Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, cattle, sheep or swine. The vegetation of tended pasture, forage, consists mainly of grasses, with an interspersion of legumes and other forbs...

s and a switch from pastoral farming
Pastoral farming
Pastoral farming is farming aimed at producing livestock, rather than growing crops. Examples include dairy farming, raising beef cattle, and raising sheep for wool. In contrast, mixed farming is growing of both crops and livestock on the same farm. Pastoral farmers are also known as graziers...

 to arable farming
Agronomy
Agronomy is the science and technology of producing and using plants for food, fuel, feed, fiber, and reclamation. Agronomy encompasses work in the areas of plant genetics, plant physiology, meteorology, and soil science. Agronomy is the application of a combination of sciences like biology,...

 had a devastating effect on populations of the Giant Gippsland earthworm leading to their classification as a protected species.

Therefore, the most reliable way to maintain or increase the levels of worm population in the soil is to avoid the application of artificial chemicals. Adding organic matter, preferably as a surface mulch, on a regular basis will provide them with their food and nutrient requirements, and also creates the optimum conditions of heat (cooler in summer and warmer in winter) and moisture to stimulate their activity.

Economic impact

Various species of worms are used in vermiculture, the practice of feeding organic waste to earthworms to decompose and compost
Compost
Compost is organic matter that has been decomposed and recycled as a fertilizer and soil amendment. Compost is a key ingredient in organic farming. At its most essential, the process of composting requires simply piling up waste outdoors and waiting for the materials to break down from anywhere...

 food waste. These are usually Eisenia fetida
Eisenia fetida
Eisenia fetida , known under various common names such as redworm, brandling worm, tiger worm and red wiggler worm, red californian earth worm, is a species of earthworm adapted to decaying organic material. These worms thrive in rotting vegetation, compost, and manure; they are epigeal...

(or its close relative Eisenia andrei
Eisenia andrei
Eisenia andrei is a close relative of the 'brandling' or 'tiger' worm, Eisenia fetida. Like its sibling species, it is epigeic, i.e. it prefers to live in compost or leaf litter rather than mineral soils....

) or the Brandling worm, also known as the Tiger worm or Red Wiggler, and are distinct from soil-dwelling earthworms.

Earthworms are sold all over the world. The earthworm market is sizable. According to Doug Collicut, "In 1980, 370 million worms were exported from Canada, with a Canadian export value of $13 million and an American retail value of $54 million."

Earthworms are also sold as food for human consumption. Noke
Noke (worms)
Noke is a culinary term used by the Māori of New Zealand to refer to earthworms, some types of native worms are local delicacies. According to Maori legend, the trickster Māui once transformed himself into a Noke Worm in order to crawl into the womb of the underworld goddess and gain everlasting...

 is a culinary term used by the Māori of 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...

, to refer to earthworms which are considered delicacies.

Taxonomy and distribution

The families, with distribution of the main ones:
  • Acanthodrilidae
    Acanthodrilidae
    Acanthodrilidae is an ancient and widely distributed family of earthworms which has native representatives in Australia, New Zealand, South Africa, South America and North America. Interestingly, no native species are known from India nor Asia...

    : Africa, midland and southeastern North America, Central and South America, Australia and Oceania.
  • Ailoscolidae
  • Alluroididae
  • Almidae
    Almidae
    The animal family Almidae includes about six genera of segmented worms.A notable peculiarity of some species in this family is a tendency to extensions of the body wall in the vicinity of or including the male pores. These extensions may be mere protuberances, as in some species of Drilocrius; or...

     (disputed): Africa, South America.
  • Criodrilidae
    Criodrilidae
    The family Criodrilidae is represented by genera Criodrilus and Biwadrilus that are limicolous and/or aquatic earthworms endemic to the Palaearctic currently known only from Europe and Japan, respectively...

  • Eudrilidae
    Eudrilidae
    Eudrilidae is a family of earthworms, mostly of Africa. One species, Eudrilus eugeniae , is widely distributed around the warmer parts of the world and cultured as the "African nightcrawler"....

    : Tropical Africa.
  • Exxidae: Central America/Caribbean.
  • Glossoscolecidae
    Glossoscolecidae
    Glossoscolecidae is a large family of earthworms which has native representatives in South and Central America. The species Pontoscolex corethrurus has a circumtropical distribution....

    : Central and northern South America.
  • Hormogastridae: Europe.
  • Lumbricidae
    Lumbricidae
    The Lumbricidae is a family of earthworms which includes most of the earthworm species well known to Europeans. About 33 lumbricid species have become naturalized around the world, but the bulk of the species are in Holarctic: from Canada and the United States The Lumbricidae is a family of...

    : Temperate Northern Hemisphere from Vancouver Island, Canada to Japan, mostly Eurasia.
  • Lutodrilidae
  • Megascolecidae
    Megascolecidae
    Megascolecidae is a large family of earthworms which has native representatives in Australia, New Zealand, Southeast and East Asia, and North America. The most ancient lineages of the family show a Gondwanan distribution and have been used as evidence of continental drift. Members of the Pheretima...

    : South East Asia, Australasia and Oceania, northwestern North America.
  • Microchaetidae
  • Ocnerodrilidae: Central and South America, Africa.
  • Octochaetidae: Central/South America, western Africa, India, New Zealand, Australia.
  • Sparganophilidae: North America.

See also

  • Caecilians of the Western Ghats
    Caecilians of the Western Ghats
    The Western Ghats are home to several species of Caecilians .Caecilians are legless, burrowing amphibians which mostly live in leaf litter, loose soil, under rocks and decaying logs. They are also found in agricultural fields and only surface during the monsoon. The body is elongated and smooth...

  • Drilosphere
    Drilosphere
    The drilosphere is the part of the soil influenced by earthworm secretions and castings. Specifically, it is the fraction of soil which has gone through the digestive tract of earthworms; or the lining of an earthworm burrow...

    , the part of the soil influenced by earthworm secretions and castings
  • The Formation of Vegetable Mould through the Action of Worms
    The Formation of Vegetable Mould through the Action of Worms
    The Formation of Vegetable Mould through the Action of Worms, with Observations on their Habits is an 1881 book by Charles Darwin on earthworms. It was his last scientific book, and was published shortly before his death...

  • Invasive earthworms of North America
    Invasive earthworms of North America
    Invasive species of earthworms, specifically from the suborder Lumbricina, are migrating and spreading through North America. Their introduction is having drastic effects on the multiple nutrient cycles in temperate or temperate-coniferous forests. These earthworms increase the cycling and leaching...

  • Soil life
    Soil life
    Soil life or soil biota is a collective term for all the organisms living within the soil.-Overview:In balanced soil, plants grow in an active and steady environment. The mineral content of the soil and its heartiful structure are important for their well-being, but it is the life in the earth that...

  • Vermicompost
    Vermicompost
    Vermicompost is the product or process of composting utilizing various species of worms, usually red wigglers, white worms, and earthworms to create a heterogeneous mixture of decomposing vegetable or food waste, bedding materials, and vermicast...

  • Worm charming
    Worm charming
    Worm charming, worm grunting, and worm fiddling are methods of attracting earthworms from the ground. The activity is usually performed to collect bait for fishing but can also take the form of a competitive sport...


Further reading

  • Edwards, Clive A., Bohlen, P.J. (Eds.) Biology and Ecology of Earthworms. Springer, 2005. 3rd edition.
  • Edwards, Clive A. (Ed.) Earthworm Ecology. Boca Raton: CRC Press, 2004. Second revised edition. ISBN 0-8493-1819-X
  • Lee, Keneth E. Earthworms: Their Ecology and Relationships with Soils and Land Use. Academic Press. Sydney, 1985. ISBN 0-12-440860-5
  • Stewart, Amy. The Earth Moved: On the Remarkable Achievements of Earthworms. Chapel Hill, N.C.: Algonquin Books, 2004. ISBN 1-56512-337-9

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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