Water beetle

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a water beetle out of water

A water beetle is a generalized name for any beetle that is adapted to living in water at any point in its life cycle. Most water beetles can only live in fresh water, with a few marine species that live in the intertidal zone or littoral zone. Water beetles rise to the water surface and take air into their tracheal systems.

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. Some families of water beetles have fringed hind legs adapted for swimming, but most do not. Most families of water beetles have larvae that are also aquatic; many have aquatic larvae and terrestrial adults.

Water Beetles (Dytiscidae). a, Beetle (Cybister sp.); b, head of beetle with feelers and gunts (Agabus); c, larva (Larva of Dyticus, Water Beetle); d, pupa (Pupa of Dyticus).

Families in which all species are aquatic in all life stages include Dytiscidae, whirligig beetles (Gyrinidae), Haliplidae, Noteridae, Amphizoidae, Hygrobiidae, Meruidae, and Hydroscaphidae.

Families in which the adults are not necessarily aquatic include Hydrophilidae, Lutrochidae, Dryopidae, Elmidae, Eulichadidae, Heteroceridae, Limnichidae, Psephenidae, Ptilodactylidae, Torridincolidae, and Sphaeriusidae.

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