WATER STRIDER

also called Pond Skater, or Skimmer, any insect of the family Gerridae (order Heteroptera), which numbers about 350 species. Water striders, often seen running or skating in groups over the surface of a pond or stream, are slender, dark coloured, and generally more than 5 millimetres (1/5 inch) long. With their short front legs they capture insects that fall onto the water surface. In crowded conditions water striders have been known to prey on each other. The middle and hind pairs of legs are long, sometimes more than twice the length of the body. The middle pair is used for propulsion, and the hind pair is used for steering. The feet (tarsi) are covered with fine, water-resistant hairs that enable the insect to remain on the water surface. Often two forms of the adult occur in the same species; one wingless, the other winged. Occasionally a third form with short wings appears. Gerris is a cosmopolitan genus of this family. All water striders live in fresh water except those of the genus Halobates, which are considered the only true salt-water-inhabiting insects. They have been seen many miles from land on tropical and subtropical ocean surfaces, feeding on the fluids of dead, floating animals.