Water Beetle — A water beetle is a beetle adapted to living in water. A number of different types are known, nearly all living in or on fresh water. The few marine species tend to live in the intertidal zone.
Many water beetles carry an air bubble underneath their abdomens, which both provides an air supply, and prevents water from getting into the spiracles. Others have the surface of their exoskeleton modified to form a plastron, or “physical gill”, which permits direct gas exchange with the water.
Most families of water beetles have larvae that are also aquatic, but the reverse is not so; many have aquatic larvae and terrestrial adults.
Types that are aquatic in all life stages include whirligig beetles (Gyrinidae), Haliplidae, Noteridae, Amphizoidae, Dytiscidae and Hydroscaphidae
Types in which the adults are not necessarily aquatic include Hydrophilidae, Lutrochidae, Dryopidae, Elmidae, Eulichadidae, Heteroceridae, Limnichidae, Psephenidae, Ptilodactylidae and Sphaeriusidae.