Water striders row across ponds by pushing against waves they make
A water strider does not swim; it stands on the surface film of a pond, held up by water-repelling hairs and long splayed legs. To move, it presses its middle legs down and back, creating a small wave whose crest it shoves against. The result can exceed a metre per second.
More than 1,700 species of these true bugs are known, and about a tenth live at sea, unusual among insects; the ocean-going genus Halobates drew scientific attention during the Challenger expedition. Most are 2 to 12 millimetres long, but the largest, Gigantometra gigas of streams in northern Vietnam and southern China, reaches about 36 millimetres, with middle and hind legs that can each top 10 centimetres.
Their bodies are carpeted with thousands of tiny hairs per square millimetre that shed rain and spray. If a wave does push one under, the hairs trap air, which floats the insect back up and gives it bubbles to breathe. Short front legs carry claws partway along, like a mantis, for seizing prey, the long middle legs row, and the hind legs steer. Oil is a different matter: experimental spills suggest it can immobilise and kill them.
Wings are optional in this family. Some populations are long-winged, some short-winged, some wingless, and some switch between broods depending on season and temperature. Long wings let an insect escape a crowded or drying pond; skipping them frees energy for producing eggs sooner. Calm, stable lakes tend to host wingless or long-winged forms, while rougher waters favour shorter wings less likely to be damaged.
Molecular studies date the family's origin to about 128 million years ago in the Cretaceous, when it split from its sister group, the Veliidae. Females glue two to twenty eggs to submerged rocks or plants; the eggs start pale and turn bright orange. Young pass through five nymph stages of about a week to ten days each, reaching adulthood in roughly 60 to 70 days depending on water temperature.
Source: Gerridae
