70 British species, 1.5-38mm long, split between aquatic and terrestrial lifestyles. In general, members of the subfamily Hydrophilinae (but also Coelostoma orbiculare (Fabricius) and some of the genus Cercyon) are aquatic, but the subfamily Sphaeridiinae are terrestrial, in dung and other organic detritus.  Most of the Cercyon spp. and all Sphaeridium are associated with dung, while still more Cercyon species occur in wet debris such as rotting seaweed.  The maxillary palps of many species are elongate, in some cases longer than the antennae, which have instead been modified for use as breathing apparatus.  The aquatic species are generally poor swimmers, moving more by walking underwater than by actively diving or swimming.