Water strider
Overview
Gerridae is a family of true bugs
Bugs
Bugs may refer to:*Heteroptera, the taxonomic order, to which belong "true bugs" insects*arthropods, an invertebrate animal having an exoskeleton, a segmented body, and jointed appendages*Bugs Bunny, an animated cartoon character...

 in the order Hemiptera
Hemiptera
Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...

, commonly known as water striders, water bugs, magic bugs, pond skaters, skaters, skimmers, water scooters, water skaters, water skeeters, water skimmers, water skippers, water spiders, or Jesus bugs. One main characteristic that sets gerrids and other true bugs apart from other insects is that the front wing is only half functional.
Encyclopedia
Gerridae is a family of true bugs
Bugs
Bugs may refer to:*Heteroptera, the taxonomic order, to which belong "true bugs" insects*arthropods, an invertebrate animal having an exoskeleton, a segmented body, and jointed appendages*Bugs Bunny, an animated cartoon character...

 in the order Hemiptera
Hemiptera
Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...

, commonly known as water striders, water bugs, magic bugs, pond skaters, skaters, skimmers, water scooters, water skaters, water skeeters, water skimmers, water skippers, water spiders, or Jesus bugs. One main characteristic that sets gerrids and other true bugs apart from other insects is that the front wing is only half functional. Rather than using it for flight, it acts as a membranous covering and the thickened part is by where claws develop. Consistent with the classification of Gerridae as true bugs, gerrids have a mouthpart evolved for piercing and sucking, Gerrids distinguish themselves by having the unique ability to walk on water. Gerridae, or water striders, are anatomically built to transfer their weight to be able to run on top of the water's surface. As a result, one could likely find water striders present in any pond, river, or lake. Scientists have identified over 1,700 species of Gerrids, 10% of them being marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

.

While 90% of Gerridae are freshwater bugs, it is the oceanic Halobates
Halobates
Halobates or sea skaters are a genus with over 40 species of water striders. While many are coastal, about five of these are able to survive and stand on the surface of the open ocean, a habitat containing very few insect species. They are predators, coastal species feeding mainly on fallen...

that make the family quite exceptional among insects. The genus Halobates was first heavily studied between 1822 and 1883 when Buchanan-White collected several different species during the Challenger Expedition
Challenger expedition
The Challenger expedition of 1872–76 was a scientific exercise that made many discoveries to lay the foundation of oceanography. The expedition was named after the mother vessel, HMS Challenger....

. Around this time, Eschscholtz discovered three species of Family Gerridae, Order Hemiptera
Hemiptera
Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...

, raising attention to the species even though little of their biology was known. Since then, the Gerridae have been continuously studied due to their ability to walk on water and unique social characteristics. Small gerrids have frequently been confused with the other semiaquatic bugs, Veliidae
Veliidae
Veliidae is a family of predatory insects in the suborder Heteroptera. They are commonly known as riffle bugs, smaller water striders or broad-shouldered water striders because the segment immediately behind the head is wider than the rest of the abdomen, unlike in the typical water striders ,...

. The most consistent characteristic used to separate these two families are internal genitalia differences. Since internal genitalia require specific training and tools to identify, it is almost impossible to tell a member of the Gerridae apart from a member of the Veliidae by external visual cues. One must study their habitat and behaviors to properly differentiate the two without looking at their specific anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...

.

Physical description

Family Gerridae are physically characterized by having hydrofuge hairpiles, retractable preapical claws, and elongated legs and body.

Hydrofuge hairpiles are small, hydrophobic microhairs. These are tiny hairs with more than one thousand microhairs per millimeter. The entire body is covered by these hairpiles, providing the water strider resistance to splashes or drops of water. These hairs repel the water, preventing drops from weighing down the body.

Antennae

Water striders have two antennae with four segments on each. Antennae segments are numbered from closest to the head to farthest. The antennae have short, stiff bristles in segment III. Relative lengths of the antennae segments can help identify unique species within the family Gerridae, but in general segment I is longer and stockier than the remaining three. The four segments combined are usually no longer than the length of the water strider head.

Thorax

The thorax of water striders is generally long, narrow, and small in size. The thorax generally ranges from 1.6 mm to 36 mm long across the species, with some bodies more cylindrical or rounder than others. The pronotum, or outer layer of the thorax, of the water strider can be either shiny or dull depending on the species, and covered with microhairs to help repel water. The abdomen of a water strider can have several segments and contains both the metasternum and omphalium.

Appendages

There are a front pair, middle, and back pair of legs. The front legs are shortest and have preapical claws adapted to puncture prey. Preapical claws are claws that are not at the end of the leg, but rather halfway through. The middle legs are longer than the first pair and shorter than the last pair and are adapted for propulsion through the water. The hind pair are the longest and are used for spreading weight over a large surface area as well as steering the bug across the surface of the water. The front legs are attached just posterior to the eyes while the middle legs are attached closer to the back legs which attach mid-thorax but extend beyond the terminal end of the body.

Wings

Some water striders have wings present on the dorsal side of their thorax, while other species of Gerridae do not- particularly Halobates. Water striders (Gerridae) experience wing length polymorphism
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...

 that has affected their flight ability and evolved in a phylogenetic manner where Gerrid populations are either long-winged, wing-dimorphic, or short-winged. Wing dimorphism
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...

 consists of summer Gerrid populations evolving different length wings than winter populations within the same species. Habitats with rougher waters are likely to hold Gerrids with shorter wings while habitats with calm waters are likely to hold long-winged Gerrids. This is due to potential for damage of the wings and ability for dispersal.

Wing polymorphism

Wing polymorphism
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...

 is important to the variety and dispersal of Gerridae. The ability for one brood to have young with wings and the next not allows water striders to adapt to changing environments. Long, medium, short, and non-existent wing forms are all necessary depending on the environment and season. Long wings allow for flight to a neighboring water body when one gets too crowded, however they can get wet and weigh a water strider down. Short wings may allow for short travel, but limit how far a gerrid can disperse. Non-existent wings prevent a gerrid from being weighed down, but prevent dispersal.

Wing polymorphism is common in Gerridae despite most univoltine populations being completely apterous (wingless) or macropterous (with wings). Apterous populations of Gerridae would be restricted to stable aquatic habitats that experience little change in environment, while macropterous populations can inhabit more changing, variable water supplies. Stable waters are usually large lakes and rivers while unstable waters are generally small and seasonal. Gerrids will produce winged forms for dispersal purposes and macropterous individuals are maintained due to their ability to survive in changing conditions. Wings are necessary if the body of water is likely to dry since the gerrid must fly to a new source of water. However, wingless forms are favored due to competition for ovarian development and wings and reproductive success is the main goal due to the selfish gene theory. Overwintering gerrids usually are macropterous, or with wings, so they can fly back to their aquatic habitat after winter. An environmental switch mechanism controls seasonal dimorphism observed in bivoltine species, or species having two broods per year. This switch mechanism is what helps determine whether or not a brood with wings will evolve. Temperature also plays an important role in photoperiodic switch. Temperatures signify the seasons and thus when wings are needed since they hibernate during winter. Ultimately, these switching mechanisms alter genetic alleles for wing characteristics, helping to maintain biological dispersal.

Nature of the ability to walk on water

Water striders are able to walk on top of water due to a combination of several factors. Water striders use the high surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...

 of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 and long, hydrophobic legs to help them stay above water. Water molecules are polar and this causes them to attract to each other. The attractive nature results in the formation of a film-like layer at the top of water. This top layer has gravity acting downward in addition to the water molecules below pulling down the upper molecules. This combination creates a touch surface tension.

Gerridae species use this surface tension to their advantage through their highly adapted legs and distributed weight. The legs of a water strider are long and slender, providing the weight of the water strider body to be distributed over a much larger surface area. The legs are strong, but have flexibility that allows the water striders to keep their weight evenly distributed and flow with the water movement. Hydrofuge hairs line the body surface of the water strider. There are several thousand hairs per square millimeter, providing the water strider with a hydrofuge body that prevents wetting from waves, rain, or spray, which could inhibit their ability to keep their entire body above the water surface if the water stuck and weighed down the body. This position of keeping the majority of the body above the water surface is called an epipleustonic position, which is a defining characteristic of water striders. If the body of the water strider were to accidentally become submerged, for instance by a large wave, the tiny hairs would trap air. Tiny air bubbles throughout the body act as buoyancy to bring the water strider to the surface again, while also providing air bubbles to breathe from underwater.

The tiny hairs on the legs provide both a hydrophobic surface as well as a larger surface area to spread their weight over the water. The middle legs used for rowing have particularly well developed fringe hairs on the tibia and tarsus to help increase movement through the ability to thrust. The hind pair of legs are used for steering When the rowing stroke begins, the middle tarsi of Gerrids are quickly pressed down and backwards to create a circular surface wave in which the crest can be used to propel a forward thrust. The semicircular wave created is essential to the ability of the water strider to move rapidly since it acts as a counteracting force to push against. As a result, water striders often move at 1 meter per second or faster.

Life cycle

Gerrids go through the egg stage, five instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...

 stages of nymphal
Nymph (biology)
In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...

 forms, and then the adult stage. Instar durations of water striders are highly correlated throughout the larval period. This means that individuals tend to develop at the same rate through each instar stage. Each nymphal stage lasts 7–10 days and the water strider molts, shedding its old cuticle through a Y-shaped suture dorsal to the head and thorax. Nympths are very similar to adults in behavior and diet, but are smaller (1 mm long), paler, and lack differentiation in tarsal and genital segments. It takes approximately 60 to 70 days for a water strider to reach adulthood, though this development rate has been found highly correlated to the water temperature the eggs are in.

Habitat

Habitats of each genus of Family Gerridae
Genus of family Gerridae No. of
marine species
Brackish
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...

Neritic
Neritic zone
The neritic zone, also called coastal waters, the coastal ocean or the sublittoral zone, is the part of the ocean extending from the low tide mark to the edge of the continental shelf, with a relatively shallow depth extending to about 200 meters...

Oceanic
Oceanic zone
The oceanic zone begins in the area off shore where the water measures 200 meters deep or deeper.It is the region of open sea beyond the edge of the continental shelf and includes 65% of the ocean’s completely open water...

Asclepios 4
Halobates group 1 39
Halobates group 2 7
Stenobates 1
Rheumatometroides 1
Rheumatobates 6

Gerridae generally inhabit surfaces of calm waters. The majority of water striders inhabit freshwater areas, with the exception of Halobates
Halobates
Halobates or sea skaters are a genus with over 40 species of water striders. While many are coastal, about five of these are able to survive and stand on the surface of the open ocean, a habitat containing very few insect species. They are predators, coastal species feeding mainly on fallen...

. Gerridae prefer an environment abundant with insects or zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...

 and one that contains several rocks or plants to oviposit eggs on. It has been studied by prevalence of water striders in varying environments, that water striders most prefer waters around 25 degrees Celsius. Any water temperature lower than 22 degrees Celsius is unfavorable. This is likely due to the fact that development rates of young are temperature dependent [5]. The cooler the surrounding waters, the slower the development of the young is. Prominent genera Gerridae are present in Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

, U.S.S.R., Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, U.S.A., S. Africa, S. America, 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...

, 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...

 and Malaysia [5]. None have been yet identified in 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...

 waters.

Diet

Gerrids undergo aquatic predation and feed on invertebrates, mainly spiders and insects, that fall onto the water surface. The water striders are attracted to this food source by the ripples produced by the struggling prey. The water strider uses its front legs as sensors for the vibrations produced by the ripples in the water. The water strider will grab onto the insect, puncture its body with its claws, and then suck out sustenance in a method called suction feeding. Gerrids prefer living prey, though they are indiscriminate feeders when it comes to terrestrial insect type. Halobates, which are found on open sea, feed off floating insects, zooplankton, and occasionally resort to cannibalism of their own nymphs. Cannibalism
Cannibalism
Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...

 often occurs, but helps to control population sizes and restrict conflicting territories. During the non-mating season when gerridae live in cooperative groups, and cannibalism rates are lower, water striders will openly share large kills with others around them. Some gerrids are collectors, feeding off sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

 or deposit surface.

Predators

Gerrids, or water striders, are preyed upon largely by birds and some fish. Petrels, terns, and some marine fish prey on Halobates
Halobates
Halobates or sea skaters are a genus with over 40 species of water striders. While many are coastal, about five of these are able to survive and stand on the surface of the open ocean, a habitat containing very few insect species. They are predators, coastal species feeding mainly on fallen...

. Fish do not appear to be the main predators of water striders, but will in cases of starvation. Scent gland secretions from the thorax are responsible for repelling fish from eating them. Gerrids are largely hunted by birds of a wide range of species dependent on habitat. Some water striders are hunted by frogs, but they are not their main food source. Water striders are also sometimes hunted by each other. Water strider cannibalism
Cannibalism
Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...

 involves mainly hunting nymphs for mating territory and sometimes for food. To escape predators, water striders will either fly away to a neighboring pond or dive under water. This avoidance of predation aids the dispersal process and thus spread of a species over a larger area of land. As species encounter new areas of land, they must learn to adapt to new environments. There are so many species of water strider partially as a result of this dispersion and adaptation over time.

Parasitism

Several endoparasites have been found in gerrids. Trypanosamatid flagellates, nematodes, and parasitic Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...

 all act as endoparasites. Water mite larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...

 act as ectoparasites of water striders.

Dispersal

Sudden increases in salt concentration in the water of gerrid habitats can trigger migration of water striders. Water striders will move to areas of lower salt concentration, resulting in the mix of genes within brackish and freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...

 bodies. Nymphal density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 also affects the dispersal of water striders. The higher density of water striders in the nymphal stage results in a higher percentage of brachypterous adults developing flight muscles. These flight muscles allow for the water striders to fly to neighboring bodies of water and mate, resulting in the spread of genes. This spread and mixing of genes can be beneficial due to a heterozygotic advantage. Generally, water striders will try to disperse in such a way to lower the density of Gerrids in one area or pool of water. Most do this by flight, but those that lack wings or wing muscles will rely on the current of their water body or flooding. Eggs in Halobates
Halobates
Halobates or sea skaters are a genus with over 40 species of water striders. While many are coastal, about five of these are able to survive and stand on the surface of the open ocean, a habitat containing very few insect species. They are predators, coastal species feeding mainly on fallen...

 are often laid on floating ocean debris and thus spread across the ocean by this drifting matter.

Mating behaviors

Sex discrimination in Gerridae is determined through communication of ripple frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

 produced on the water surface. Males predominantly produce these ripples in the water. There are three main frequencies found in ripple communication: 25 Hz as a repel signal, 10 Hz as a threat signal, and 3 Hz as a courtship signal. An approaching gerrid will first give out a repel signal to let the other water strider know they are in its area. If the other gerrid does not return the repel signal, then the bug knows it is a female and will switch to the courtship signal. A receptive female will lower her abdomen and allow the male to mount her and mate. A non-receptive female will raise her abdomen and emit a ripple signal. Males that are allowed to mate stay attached to the same female for the entire reproductive season. This is to ensure that the female's young belong to the mounting male and thus guarantee the spread of his genes. Females oviposit, or lay their eggs, by submerging and attaching the eggs to stable surfaces such as plants or stones. Some water strider species will lay the eggs at the water edge if the body of water is calm enough. The amount of eggs laid depends on the amount of food available to the mother during the reproductive season. The availability of food and dominance among other gerrids in the area both play crucial roles in the amount of food obtained and thus, resulting fecundity
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...

. Water striders will reproduce all year long in tropical regions where it remains warm, but only during the warm months in seasonal habitats. Gerrids that live in environments with winters will overwinter in the adult stage. This is due to the large energy cost which would need to be spent to maintain their body temperature at functional levels. These water striders have been found in leaf litter or under stationary shelters such as logs and rocks during the winter in seasonal areas. This reproductive 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...

 is a result of shortening day lengths during larval development and seasonal variation in lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

 levels. Shorter day length signals the water strider of the coming temperature drops, also acting as a physical signal the body uses to store lipids throughout the body as food sources. Water striders use these lipids to metabolize during their hibernation
Hibernation
Hibernation is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. Hibernating animals conserve food, especially during winter when food supplies are limited, tapping energy reserves, body fat, at a slow rate...

. The length of the hibernation
Hibernation
Hibernation is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. Hibernating animals conserve food, especially during winter when food supplies are limited, tapping energy reserves, body fat, at a slow rate...

 depends when the environment warms and the days become longer again.

Social behavior

Kin discrimination is rare in Gerridae, only really being seen in Halobates
Halobates
Halobates or sea skaters are a genus with over 40 species of water striders. While many are coastal, about five of these are able to survive and stand on the surface of the open ocean, a habitat containing very few insect species. They are predators, coastal species feeding mainly on fallen...

. Without hunger playing a role, several studies have shown that neither A. remigis nor L. dissortis parents preferentially cannibalize on non-kin. Those two species are highly prevalent in American
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 waters. These species do not show familial tendencies, leaving their young to forage on their own. Females cannibalize more on young than males do and, in particular, on first-instar nymphs. Young must disperse as soon as their wings are fully developed to avoid cannibalism and other territorial conflicts since the parents nor siblings can identify members genetically related to themselves.

Gerridae are territorial insects and make this known by their vibration patterns. Both female and male adult Gerridae hold separate territories, though usually the male territories are larger than the female. During the mating season, gerrids will emit warning vibrations through the water and defend both their territory and the female in it. Even though gerridae are very conspicuous, making their presence known through repel signals, they often live in large groups .. These large groups usually form during the non-mating season since there is less need to compete. Instead of competing to reproduce, water striders can work together to obtain nutrition and shelter outside of the mating season. Water striders will attempt to disperse when these groups become too dense. They do so by flying away or cannibalizing.

See also

  • Veliidae
    Veliidae
    Veliidae is a family of predatory insects in the suborder Heteroptera. They are commonly known as riffle bugs, smaller water striders or broad-shouldered water striders because the segment immediately behind the head is wider than the rest of the abdomen, unlike in the typical water striders ,...

     (Smaller water strider)
  • Animal locomotion on the surface layer of water
    Animal locomotion on the surface layer of water
    Animal locomotion on the surface layer of water is the study of animal locomotion in the case of small animals that live on the surface layer of water, relying on surface tension to stay afloat....

  • Denny's paradox
    Denny's paradox
    In the study of animal locomotion on the surface layer of water, Denny's paradox refers to the apparent impossibility of surface-dwelling animals such as the water strider generating enough propulsive force to move...



External links

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