These beetles are generally oval in shape, with lengths from 1.5 to 5 mm, and generally yellowish to light brown in color, frequently with light and dark patterns dotted with 10 or more rows of punctures. The eyes are distinctly protruding from a smallish head, and the legs have long swimming hairs, but the family's most distinctive characteristic is the large coxal plates underneath, which extend back to cover most of the abdomen, and are used as air storage supplementing the air carried under the elytra.
Haliplids live in the aquatic vegetation around the edges of small ponds, lakes, and quiet streams. Adults are omnivorous, eating insect eggs, small crustaceans, hydrozoan polyps, and algae, while the larvae eat only algae.
The species of Peltodytes deposit eggs on the surface of aquatic plants, while Haliplus chew out a cavity in the plants for their eggs. There are three instars, and pupation takes place on land in a chamber constructed by the larva.
The classification of haliplids as a separate group is unquestioned, and most workers believe they developed from terrestrial beetles separately from other types of water beetles. Until 2005, the family was in need of revision, the last general catalog being published by A. Zimmermann in 1920, that was recently replaced by catalogue by B.J. van Vondel (2005). Hungerford's crawling water beetle, Brychius hungerfordi Spangler, is an endangered species found only in Michigan and Ontario.
Tree of Life page, with pictures FWS info on Brychius hungerfordi