Aquatic Coleoptera (Water Beetles)

Hydroscaphidae adults (Myxophaga) crawl to the surface to renew their air supply. Elmidae and Dryopidae adults (Polyphaga) usually live in oxygen-rich water and maintain a plastron of air that is carried on hydrofuge hairs. The plastron acts as a physical gill, with oxygen for respiration diffusing into it from the water, and carbon dioxide from respiration diffusing out into the water. Other Polyphaga adults (Helophoridae, Hydrochidae, Hydrophilidae, Hydraenidae, and Curculionidae) also maintain an air supply on hydrofuge hairs, but must renew the air by swimming (most Hydrophilidae) or crawling (Curculionidae, Hydraenidae, Helophoridae, Hydrochidae, and some Hydrophilidae) to the surface when the water contains too little oxygen for plastron respiration. Unlike Adephaga, adult polyphaga break the surface film with their antennae.

Review: Overview of Insecta