Water Scavenger Beetles
Pictorial Key
Family: Hydrophilidae
Genus: Tropisternus
Species: Lateralis
Size: 6mm-11mm
Beadlike Antennae
Hydrophilidae beetles are characterized by the 4 segment club on the end of their beadlike antennae. The body is oval or elliptical, convex on the dorsal side and flat on the ventral side. The hind tarsi are flat and hairy, used for swimming. Generally black and shiny, these beetles range from 1-40 mm in length. They are aquatic or semi-aquatic. Mostly herbivorous, but some will eat dead animal tissue or insects. The aquatic species are found in quiet pools and areas of water rife with vegetation. The two genera of hyrdophilidae can be distinguished by their swimming styles. Predacious water beetles swim using their legs in unison whereas the water scavenger beetles move them alternately, like walking.
There are 15 members of the Tropisternus genus and they range from 8-12 mm. Tropisternus lateralis, pictured here, is found from Canada to Florida and as far west as the Rockies. It is common in temporary or permanent pools. In fact, it is one of the first water scavenger beetles found in newly formed pools, such as those formed in rainbuckets or wheelbarrows.