wheel bug

wheel bug, (Arilus cristatus), species of large, primarily North American assassin bug named for the distinctive wheel-like crest on the top of its thorax. The insect is a top predator with a wide range of prey, including defoliating caterpillars, sawfly larvae, and the invasive brown marmorated stink bug, and is generally considered beneficial to gardens and wild ecosystems. It is found throughout much of the southern and eastern United States and into Mexico and parts of Central America. Wheel bugs are not aggressive but have a painful bite if handled.

Physical description

As an insect, the wheel bug has a body formed of a head, a thorax, and an abdomen as well as six legs. The front pair of legs is raptorial, meaning they are used for catching and grasping prey. The adult is brown to gray and large, about 25 to 36 mm (1 to 1.5 inches), and is recognized by the notched semicircular crest on the top of the thorax, for which it is named. Females are typically larger than males. The young nymph is black with a red, upward-curving abdomen and lacks the wheel-like crest; they are sometimes confused with spiders because of their long, spindly legs.

The insect has a long neck and narrow head topped with bulbous compound eyes and a pair of long antennae. Like other predatory assassin bugs, the wheel bug uses its short three-segmented beak to pierce its soft-bodied prey. The venomous saliva is pumped into a victim through a channel in the wheel bug’s beak. The digested body fluids of the prey are then pumped into the wheel bug’s stomach through another channel in the beak. When not in use, the retractable mouthparts characteristically tuck into a groove between the front legs, beneath the head and thorax.

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As is characteristic of most true bugs (members of the suborder Heteroptera), the adult wheel bug has two pairs of wings. The unusual forewings (called hemelytra) are stiff and have an oblique line that abruptly separates a leathery basal half from a membranous apical half. The hind wings are thin, delicate membranes that are folded under the protective forewings when at rest. They are slow, noisy, and clumsy fliers.

Life cycle and natural history

The wheel bug is commonly found in meadows and woodlands, on trees and shrubs in neighborhoods, and occasionally on buildings, especially near outdoor lights at night. The insect uses its exceptional vision to stalk its prey. Adults mate in the summer and fall, and shortly thereafter the females lay several dozen eggs on small twigs in trees and shrubs. The eggs are barrel-shaped and are laid on end in a tight, often hexagonal cluster. The eggs overwinter, and small nymphs emerge in the early spring. They molt as they grow, progressing through five instars (stages of metamorphosis) before reaching adulthood by midsummer.