Whirligig beetles look like a blur as they gyrate endlessly around each other on 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.
The larvae are pale, elongated, flattened, with 3 pairs of crawling legs and 8 pairs of featherlike gills protruding from the sides of the abdomen.
Adult length: about ¼–¾ inch (varies with species).
Statewide.
Habitat and Conservation
Whirligig beetles occur in many types of aquatic habitats, including ponds, lakes, and streams. They can swim almost as effortlessly underwater as they do on the surface, making them difficult to catch. Their wings are well developed, so whirligigs can fly to a new home if their pond or stream should dry up.
Adult whirligig beetles trap air beneath their wings, enabling them to dive underwater for extended periods.
Food
These beetles and their larvae are carnivorous.
The larvae eat other aquatic insects and invertebrates.
The adults often feed on land insects that fall into the water. They are attracted to the waves caused by the struggling insect, and sometimes a group of whirligigs can be seen crowding around one of these meals, each trying to take bites of it. They also function as scavengers, eating dead creatures, too.
Life Cycle
Eggs are laid on the surfaces of submerged aquatic plants. The larvae are not as commonly seen as the adults and spend most of their time crawling on the bottom or sometimes swimming with sinuous movements. When grown, the larvae crawl out of the water and pupate on nearby plants. The adults return to water and overwinter in mud and debris. In spring, they emerge from hibernation and form hunting groups.
Human Connections
Sit by a pond sometime and watch the mesmerizing gyrations and circular patterns made by these sleek insects on the surface of the water. The family name, Gyrinidae, has the same root word as "gyrate."
Whirligig beetles employ a simple form of radar when they use water ripples to detect food or other whirligigs on the surface. Like bats, which use a kind of sonar, they pioneered “technologies” that humans have only fairly recently developed.
Whirligigs used to be fairly common spinning toys (such as pinwheels and tops) that children played with. Now, the whirligigs most people see are spinning decorations in people's yards, made to look like birds or cool-looking circular wind spinners.
Ecosystem Connections
These small predators and scavengers clean the water of dead or dying insects and help control the populations of other aquatic invertebrates. In turn, they and the larvae are eaten by fish and other predators.
Behavior is one of the ways animals adapt to their environment. These insects have some pretty interesting behavioral adaptations having to do with their location among other whirligig beetles in a group. Whether they swim on the margins of the group or nearer the center, or whether they "draft" behind others or swim in the front of a line, is influenced by things like their sex, their physical condition, and how hungry they are.
