; subclass Pterygota, order Coleoptera)
Family of fast-moving, gregarious beetles which swim in small circles on the surface of ponds. They have dark, shiny elytra. The antennae are short and stout. The eyes are divided for vision above and below the water surface. The middle and hind legs are paddle-like swimming structures, but the fore legs are modified for grasping prey. They feed on insects found on the water surface. Larvae are predatory and bottom-dwelling, with 10 pairs of feathery, external gills. There are 700 species.
Subjects: Zoology and Animal Sciences.