Wheel bug
The wheel bug (Arilus cristatus) is the largest assassin bug in North America. It grows to about 1½ inches, is grey to brown, and has a toothed, cog-like crest on its back. It preys on caterpillars, moths, Japanese beetles, stink bugs and other insects, and extension entomologists count it as beneficial. It is not aggressive, but it bites if handled. A University of Kentucky entomologist reports that the pain lasts several minutes. Leave it where it is.
At a glance
- Kind
- Wild — not sold
- Adult
- 1–1½ in (25–38 mm); grey to brown
- Nymph
- Red and black when small; no wheel
- Eggs
- Several dozen barrels, glued on end to twigs
- Generations
- One a year; the eggs overwinter
- Bite
- Painful for several minutes; not aggressive
How it works
In autumn the female glues several dozen barrel-shaped eggs on end, in a cluster, to a small twig of a tree or shrub. The Missouri Department of Conservation describes the clusters as six-sided. The eggs overwinter and hatch in early spring. The small red-and-black nymphs, which can look like spiders or ants, spread onto nearby trees and shrubs and go through five nymphal stages. They have no wheel until they mature around midsummer. Adults are common from midsummer through autumn.
Like all assassin bugs, it seizes prey with enlarged front legs, stabs it with a stout beak held out in front like an elephant's trunk, and injects digestive enzymes before draining the body fluids. Kentucky Extension lists caterpillars, moths and other soft-bodied insects as prey, the Missouri Department of Conservation adds Japanese beetles, and WSU reports wheel bugs eating brown marmorated stink bugs. When disturbed, an adult can push a bright orange scent gland out of its rear end. Adults often turn up near outdoor lights close to woods at night. They come for the other insects there, not for the light.
What it is confused with
Nothing else in North America has the wheel, so the adults are easy to name. The nymphs and the bite cause the confusion.
- Also goodOther assassin bugs — Most garden species are ½–¾ inch long. The wheel bug reaches 1¼–1½ inches and is the only one with a cogwheel crest. See assassin bugs.
- Also goodWheel bug nymphs — Young nymphs are red and black with long legs and can pass for spiders or ants. Older nymphs turn grey like the adult, with short wing pads and still no wheel.
- PestKissing bugs — Smaller (½–1 inch), most with orange or red stripes around the edge of the body, and no crest. Their bite is usually painless and unnoticed; a wheel bug's is not.
- PestLeaf-footed bugs — Plant-feeders of a similar size, with flattened, leaf-like flaps on the hind legs and no crest. Often mistaken for assassin bugs.
How to keep it around
Wheel bugs cannot be bought, and there is no need to. They live in meadows, trees and shrubs. Keeping them means not destroying them at any stage.
- Trees, shrubs and meadow edges, where wheel bugs live and hunt
- Leave the egg clusters, clusters of small brown barrels glued to twigs, when pruning in autumn and winter
- No broad-spectrum insecticide sprays on the trees and shrubs where they hunt
- Leave adults on walls and near outdoor lights alone, since they came for the other insects
- Move one with a jar and a card, never bare hands
Pesticide sensitivity
None of the sources read tests insecticides on wheel bugs specifically. Maryland Extension's advice for assassin bugs as a group is to avoid broad-spectrum insecticides. Open the compatibility matrix →
When to choose something else
A wheel bug is a welcome resident, not a control. Look elsewhere when:
- Stink bugs are getting into the house — see brown marmorated stink bug for keeping them out
- Spotted lanternflies are on your trees — predators are not a proven control; scrape egg masses and follow the spotted lanternfly advice
- Japanese beetles are stripping plants — see Japanese beetle; a wheel bug takes them one at a time
- Caterpillars are defoliating a crop — use Bt kurstaki
Wheel bug by target
What it eats and when it turns up differ by pest. Each page below is the picture for one target.