Curtis Young (OSU Extension, Van Wert County) brought an oak sample to the OSU Master Gardener Volunteer Diagnostic Workshop Monday in Miami County that included wheel bug (Arilus cristatus) nymphs in various instar stages of development including some late instars. This means the unusual looking adults will soon be lurking among the leaves of trees and shrubs in Ohio in search of prey.
Wheel bugs spend the winter in the egg stage. Eggs hatch in the spring and the bugs pass through five nymphal instar stages as they mature to adults. Nymphs in the 1st – 4th instar stages march around on long, spindly legs with their curved abdomens tipped-up causing them to superficially resemble spiders. The abdomens of 5th instars are flattened and held in a horizontal position.
The descriptive common name for the insect comes from the adults. They sport a peculiar morphological feature that rises from the top of the bug's thorax. The structure looks like half of a cog-wheel, with the gear teeth clearly visible. No other insect in North America has this type of structure on its thorax. Wheel bugs are big, measuring over 1 1/4" long, and their color varies from light gray to bluish-gray to grayish-brown. There is one generation per season.
Caterpillars and sawfly larvae are favored table fare of this impressively large predator; however, they will not turn their beaks up at other arthropod meat morsels. The bugs belong to the Reduviidae family which are collectively known as assassin bugs; a name that clearly describes how these stealthy hunters make a living.
As with all predatory bugs, wheel bugs are equipped with piercing-sucking mouthparts that are used to inject paralyzing and pre-digestive enzymes into their prey. They then suck the essence-of-insect from their hapless victims.
While these are beneficial insects, they should not be handled. All members of the family are capable of delivering a painful bite to people. The pain of a wheel bug bite has been described by those who have suffered the wheel of misfortune as being equal to or more powerful than a hornet sting, and the wound may take over a week to heal. Just leave them alone, don't kill them, and let them slay insects we don't want in our landscapes and gardens.