Wikipedia
Hydrophilidae, also called water scavenger beetles, is a family of chiefly aquatic beetles. Aquatic hydrophilids are notable for their long maxillary palpi, which are longer than their antennae. Several of the former subfamilies of Hydrophilidae have recently been removed and elevated to family rank; Epimetopidae, Georissidae (= Georyssinae), Helophoridae, Hydrochidae, and Spercheidae (= Sphaeridiinae). Some of these formerly-included groups are primarily terrestrial or semi-aquatic.
The vernacular name water scavenger beetles is not an accurate description of their habit. With rare exceptions, the larvae are predatory while the adults may be vegetarians or predators in addition to scavenging. Many species are able to produce sounds.
Species of Hydrophilus are reported as pests in fish hatcheries. Other species are voracious consumers of mosquito larvae, and have potential as biological control agents. There are 2,835 species in 169 genera