The Gerridae are a family of insects in the order Hemiptera, commonly known as water striders, water skeeters, water scooters, water bugs, pond skaters, water skippers, water gliders, water skimmers or puddle flies. Consistent with the classification of the Gerridae as true bugs (i.e., suborder Heteroptera), gerrids have mouthparts evolved for piercing and sucking, and distinguish themselves by having the unusual ability to walk on water, making them pleuston (surface-living) animals. They 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. Over 1,700 species of gerrids have been described, 10% of them being marine.
While 90% of the Gerridae are freshwater bugs, the oceanic Halobates makes the family quite exceptional among insects. The genus Halobates was first heavily studied between 1822 and 1883 when Francis Buchanan White collected several different species during the Challenger Expedition.
Description
The family Gerridae is 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 mm.
Size
They are generally small, long-legged insects and the body length of most species is between . A few are between .
Among widespread genera, the North Hemisphere
Aquarius includes the largest species, generally exceeding , at least among females, and the largest species averaging about .
[ but it appears to be reversed in the largest species, the relatively poorly known Gigantometra gigas of streams in northern Vietnam and adjacent southern China. It typically reaches a body length of about in wingless males and in winged females (winged males, however, only average marginally larger than females). In this species each middle and hind leg can surpass .]
Antennae
Water striders have two antennae with four segments on each. Antennal segments are numbered from closest to the head to farthest. The antennae have short, stiff bristles in segment III.
Thorax
The thorax of water striders is generally long, narrow, and small in size. It generally ranges from 1.6 mm to 3.6 mm long across the species, with some bodies more cylindrical or rounder than others.
Appendages
Gerridae have front, middle, and back 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, like mantises. 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 is the longest and is 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 midthorax 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 experience wing length polymorphism that has affected their flight ability and evolved in a phylogenetic manner where populations are either long-winged, wing-dimorphic, or short-winged.
Evolution
Cretogerris, from the Cretaceous (Albian) Charentese amber of France, was initially suggested as a gerrid.
Molecular analysis suggest an origin of the family Gerridae about 128 Million years ago (Mya) in the Cretaceous, splitting from the sister group Veliidae, with whom they share a single origin of rowing as a locomotive mechanism. According on the transcriptome-based phylogeny, Gerridae is a Clade.
Wing polymorphism
Wing polymorphism (i.e., the presence of multiple wing morphs in a given species) has independently evolved multiple times in Gerridae, as well as complete wing loss,
Wing polymorphism is common in the Gerridae despite most univoltine populations being completely apterous (wingless) or macropterous (with wings).[Koga, Hayashi. 1991. Territorial behavior of both sexes in the water strider Metrocoris histrio (Hemiptera: Gerridae) during the mating season. Journal of Insect Behavior, Volume 6 (1).] Apterous populations of gerrids would be restricted to stable aquatic habitats that experience little change in environment, while macropterous populations can inhabit more changing, variable water supplies.
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 of water and long, hydrophobic legs to help them stay above water.
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, allowing the weight of the water strider body to be distributed over a large 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.
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.
Life cycle
Gerrids generally lay their eggs on submerged rocks or vegetation using a gelatinous substance as a glue. Gravid females carry between two and twenty eggs. The eggs are creamy white or translucent, but become bright orange.
Gerrids go through the egg stage, five instar stages of nymphal forms, and then the adult stage. Instar durations of water striders are highly correlated throughout the larval period.[Klingenberg, C. 1996. Individual Variation of Ontogenies: A Longitudinal Study of Growth and Timing. Evolution, Volume 50 (6). Evolution] 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.
Ecology
Habitat
+ Gerridae genera inhabiting marine and brackish habitats |
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Gerridae generally inhabit surfaces of calm waters. The majority of water striders inhabit freshwater areas, with the exception of Asclepios, Halobates, Stenobates and a few other genera, which inhabit marine waters.[ Gerridae prefer an environment abundant with insects or zooplankton 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 .]
Diet
Gerrids are aquatic predators and feed on invertebrates, mainly spiders and insects, that fall onto the water surface.[Stonedahl, Lattin. 1982. The Gerridae or Water Striders of Oregon and Washington (Hemiptera:Heteroptera), Oregon State University, Pp 1-36.
Gerridae ] Halobates, which are found on open sea, feed off floating insects, zooplankton, and occasionally resort to cannibalism of their own nymphs.
Predators
Gerrids, or water striders, are preyed upon largely by birds and some fish. Petrels, terns, and some marine fish prey on Halobates.
Parasites
Several endoparasites have been found in gerrids. Trypanosamatid flagellates, nematodes, and parasitic Hymenoptera all act as endoparasites.
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 bodies.[Kishi, M., Harada, T., & Fujisaki, K. 2007. Dispersal and reproductive responses of the water strider, Aquarius paludum (Hemiptera: Gerridae), to changing NaCl concentrations. European Journal of Entomology, 104(3), Pp 377-383. Dispersal] Nymphal population density 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.[Harada, T., Tabuchi, R., & Koura, J. 1997. Migratory syndrome in the water strider Aquarius paludum (Heteroptera: Gerridae) reared in high versus low nymphal densities. European Journal of Entomology, 94(4), Pp 445-452. Density and Migration] 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 are often laid on floating ocean debris and thus spread across the ocean by this drifting matter.
Mating behavior
Sex discrimination in some Gerridae species is determined through communication of ripple frequency produced on the water surface.[Blanckenhorn, W. 1991. "Fitness consequences of foraging success in water striders (Gerris remigis; Heptroptera; Gerridae)" Behavioral Ecology, Volume 2 (1). Foraging] 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.
Social behavior
Kin discrimination is rare in Gerridae, only really being seen in Halobates. Without hunger playing a role, several studies have shown that neither Aquarius remigis nor Limnoporus dissortis parents preferentially cannibalize on non-kin.[Carcamo, Spence. 1994. Kin Discrimination and Cannibalism in Water Striders (Heteroptera: Gerridae): Another Look. Oikos Volume 70 (3). Cannibalism] Those two species are highly prevalent in United States waters. These species do not show tendencies, leaving their young to forage on their own. Females cannibalize more on young than males do and, in particular, on first-instar nymphs.
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.
In popular culture
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In the video game Super Mario 64, in the level Wet-Dry World, there are enemies named Skeeter that are based on water striders and their movement. The name comes from "water skeeter", an alternative name for water striders.
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In the 2002 film The Tuxedo, water striders are genetically modified by to have bacteria that can spread from person to person, causing severe dehydration and instant death.
See also
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Veliidae (Smaller water strider)
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Animal locomotion on the water surface
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Denny's paradox
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List of Gerridae genera
External links
