Any of numerous aquatic beetles usually having a smooth oval body and flattened hind legs for swimming.
Any of numerous oval flattened aquatic beetles (as a diving beetle or whirligig beetle) that swim by means of their fringed hind legs which act together as oars.

A true bug: large aquatic bug adapted to living in or on the surface of water.
Any of various small arthropods and especially insects that frequent damp or wet places: as german cockroach; water boatman; any of various large aquatic bugs (family Belostomatidae) with the hind legs flattened and used for swimming

A true bug: large aquatic bug adapted to living in or on the surface of water.
Any of various small arthropods and especially insects that frequent damp or wet places: as german cockroach; water boatman; any of various large aquatic bugs (family Belostomatidae) with the hind legs flattened and used for swimming