Gerridae

The Gerridae are a family of insects in the order Hemiptera, commonly known as water striders, water skeeters, water bugs, pond skaters, water skippers, or Jesus bugs. 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 Buchanan-White collected several different species during the Challenger Expedition. Around this time, Eschscholtz discovered three species of the Gerridae, bringing attention to the species, 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, the Veliidae. 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. 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. 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. They are generally small, long-legged insects and the body length of most species is between 2 and 12 mm (0.08–0.47 in). A few are between 12 and 25 mm (0.47–0.98 in). Among widespread genera, the North Hemisphere Aquarius includes the largest species, generally exceeding 12 mm (0.47 in), at least among females, and the largest species averaging about 24 mm (0.94 in). Females typically average larger than males of their own species, 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 36 mm (1.42 in) in wingless males and 32 mm (1.26 in) in winged females (winged males, however, only average marginally larger than females). In this species each middle and hind leg can surpass 10 cm (4 in). 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. 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. 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. 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. 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 mantids. 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.