A wheel bug is a bizarre-looking insect you'll see in landscapes and other areas late in the year. It may be a bit of a stretch, but I think it resembles a stegosaurus, the dinosaur with prominent plates on its back, or the triceratops, with the rounded structure behind its head. Wheel bugs have a half-wheel-shaped structure just behind its head, resembling a gear wheel with teeth. Its scientific name is Arilus cristatus.
Timothy Gibb, retired Purdue Extension entomologist, authored a short publication on this insect.
“Wheel bugs are in the assassin bug family,” he said. He explained that there is one generation each year, and nymphs often have an orange or red-colored abdomen. Adults can reach up to 1.5 inches long. They both have tubular heads with prominent beaks (a straw-like mouthpart).
“In nymphs or adults this beak is used much like a knight’s lance that is plunged into their prey for food or into their enemies for self-defense,” he said. “Salivary fluids are injected that dissolve the prey’s insides into a slurry. The slurry is then sucked out of the prey insect, leaving behind the discarded shell of the victim.” That’s pretty graphic, and it describes the practices of many species of assassin bugs, not just the wheel bug.
Caterpillars, sawfly larvae, and other soft-bodied pest insects are typical prey of wheel bugs, making them a beneficial insect. “The biggest drawback is that they can inflict a painful bite to unwary people who handle them carelessly,” said Gibb. “The bite of a wheel bug is serious and may take months to heal (sometimes leaving a small scar), so caution is advised when handling them.
Gibb said that wheel bugs are slow-moving and often hide on plants or on buildings. They have membranous wings, allowing for clumsy, noisy flight. Although they are common in Indiana, first-time spotters of these insects are often alarmed by their appearance.