Whirligig Beetles - Gyrinidae

One family of beetles, the Gyrinidae, favors the still surfaces of ponds, rivers, and streams. Common throughout the southern United States, they are usually seen swimming in groups in a seemingly frenzied fashion, each trailing a wake of tiny arches, whirls, and spirals. As a result, they are best known as the "whirligig beetles."

These oval beetles accomplish their rapid movements by means of their flattened, paddle-like middle and hind legs. They are usually observed on the surface, but are equally at home swimming under the surface. They have very strongly developed wings, and are easily able to fly from one still-water pond to another. If picked up, whirligig beetles give off a fruity odor. Dineutes americanus, for example, has an apple like odor.

The whirligig beetles are predaceous, feeding on the larvae of the mayfly and other small animals living near the water's surface; they will even eat each other. Some species are nocturnal. About V2 inch in length, they are bluish-black or black with a lustrous brown cast, and are shaped like a slightly flattened egg.

The strangely shaped compound eyes of the whirligig beetle provide it with a kind of split vision-it is sometimes said that this insect has 4 eyes instead of 2. The eyes on the underside of the head look down into the water while the upper pair provides the whirligig beetle with a view of activities above water level.

Whirligig females lay their eggs in rows or clusters on the undersurfaces of leaves of aquatic plants. Water lilies and pondweed are preferred. The larvae are long and segmented, with tracheal gills resembling tiny tufts of feathers. They float on the surface of the water, propelling themselves with snakelike movements. They feed on fly larvae and other insects.

The pupal stage occurs on land-in small cells made of mud that the young beetles laboriously haul from the water's edge.