Whirligigs look like a blur as they gyrate endlessly around each other on the the water. These beetles are oval, streamlined and usually blackish, sometimes bronzy or metallic. The forelegs are long and slender; the middle and hind legs are short, flattened and fold tightly under the body. One common species is Dineutus americanus.
Whirligigs can be distinguished from all other beetles by their short, clubbed antennae and their two pairs of compound eyes—one pair above the water, and one pair below—which helps them to quickly and accurately capture their prey while also evading predators.
Like other beetles, whirligigs have membranous hindwings that are covered by forewings that have been modified into thick, heavy, shields. When the wings are closed, the two shieldlike forewings form a straight line down the back.
Larvae are pale, elongated, flattened, with 3 pairs of crawling legs and 8 pairs of featherlike gills protruding from the sides of the abdomen.