Whirligig beetles are native to the temperate and tropical regions throughout the world, spending most of their life at the surface of the water. Their eyes are divided for vision in both water and air, and they can dive to considerable depths. Like the diving beetles, they are equipped with an air cavity under the wing covers. They hibernate during the cold months of the year, but emerge periodically for their characteristic whirling dances. The adults are lustrous black above and are yellow, black, or brown below. The body, like that of the diving beetles, is elliptical and convex.
Water scavenger beetles, with about 2000 species, are worldwide in distribution, but abundant in the warmer regions. Most species feed on vegetable matter, but some prey on small aquatic creatures. They are usually dark colored and shiny and elliptical in shape. Water scavenger beetles do not swim as rapidly as the diving or whirligig beetles; most species are aquatic or amphibian, but a few are terrestrial.
Scientific classification: Water beetles belong to the order Coleoptera. True, or diving, water beetles make up the family Dytiscidae. Whirligig beetles make up the family Gyrinidae. Water scavenger beetles make up the family Hydrophilidae.