Previously, the endemic water scavenger beetle fauna of Hawaii was thought to consist of two described species of Limnoxenus Motschulsky. Both species inhabit flowing streams and sidepools, and have anatomies consistent with this habitat; a flat, elongate body and long meso- and metatarsal swimming hairs. Recent collecting efforts have yielded at least four additional species, including a second lineage that is restricted to algal covered rock seeps and waterfalls. These three hygropetric species have evolved a more compressed body form, reduced to nearly absent swimming hairs, and in some cases brachypterous metathoracic wings. Wing loss is very unusual for aquatic beetles, especially for taxa within the aquatic subfamily Hydrophilinae. Larvae and adults of both stream and hygropetric species are found together in their respective habitats. The phylogenetic relationships among these lineages and others in the Hydrophilinae indicate that the closest relatives are found in Australia and New Caledonia.