What Is a Wheel Bug?
A wheel bug (Arilus cristatus) is a fairly large member (up to 1.5 inches) of the family commonly known as assassin bugs. According to Dan Young, entomology professor and director of the University of Wisconsin’s Insect Research Collection, they’re top predators in the insect world. “They use their sucking mouthparts to pierce and ultimately feed on the fluid, or semi-liquified, contents of their prey,” he says.
What Does a Wheel Bug Look Like?
As adults, these bugs are easy to identify due to the cogwheel-shaped crest on their back, called a pronotum. Their large, elongated, gray-brown bodies come to a rounded point at the back, while their heads are much smaller and sport a pair of long, curved antennae.
Rather than a mouth, they have piercing-sucking mouthparts that are housed in a beak-like mouthpiece called a proboscis at the front of their head. They extend extend their proboscis, pierce the prey, inject a toxic saliva that paralyzes and partially digests the prey, then suck out and feed on the contents of their body. Females are generally larger than males.
In their nymph form, wheel bugs look different. At a quick glance you might mistake them for a long-legged spider, but a closer look reveals they only have six legs.
They often boast plump red-orange abdomens, but they lack the distinctive wheel-shaped pronotum. They start out very small, gradually increasing in size as they molt and grow.
Similar Look-Alike Bugs
The wheel-like structure on their back makes this garden visitor easy to identify, but there are a few insects that might trick you at first glance. Other assassin bugs, leaf-footed bugs, spined soldier bugs, and western conifer seed bugs all share a similar body shape.
With that said, as long as you can get a good look, it should be easy to spot the distinctive spiked arch on a wheel bug’s back.
What Do Wheel Bugs Eat?
Wheel bugs have a wide-ranging diet of other insects, including unwelcome visitors like Japanese beetles, cabbage white caterpillars, tent caterpillars, aphids, and more. They even feed on the invasive brown marmorated stink bug, which most other predators avoid.
“As top predators within insect food webs, assassin bugs like A. cristatus are most definitely beneficial in gardens,” Dan says. “They help to feed on and control the populations of other insects that would be considered as pests. Wheel bugs are very cool beasties, and they don’t get nearly the positive press they deserve!”
Do Wheel Bugs Bite People?
While wheel bugs make welcome garden guests, it’s very important to let them do their job undisturbed. Touching one will likely provoke a defensive attack that can be incredibly painful. It’s not a true bite, so to speak, because they don’t have mouths. Instead, it’s more of a stab. The sharp tip of their proboscis pierces the skin, and then it delivers the same enzymes the bug uses to liquify prey.
The toxins also provoke a histamine response of varying-but-uncomfortable severity. Many people experience piercing pain and numbness that lasts for days, weeks, or even months. Dan notes, “Since some individuals will be more sensitive than others, the reaction will likely vary.” Fortunately, these toxins are not life-threatening and are not known to cause long-term effects.
When you see a wheel bug or its nymph, take care not to touch it. If wheel bugs are common in your yard, wear gloves while working in your garden.
When and Where Will Gardeners See a Wheel Bug?
You’ll mainly find these insects in the southeastern United States, though they’ve been reported as far west as California. Their usual range extends as far north as Rhode Island, and southwest through Texas. They’re more active during the warmer summer months. They overwinter as eggs, hatching out into nymphs in the spring.
Even if you don’t spot a wheel bug, you might hear or smell one. They make a chirping sound, which is produced by rubbing the tip of their proboscis against their bodies. This insect also has scent glands that release a pungent odor when they’re disturbed, though it’s not as strong as that of stink bugs.
Use these warning signs to be on the lookout so you can avoid a potentially painful bite!
Next, read about another fascinating garden bug the praying mantis.
About the Expert
Dan Young is an entomology professor and director of the University of Wisconsin’s Insect Research Collection (WIRC). He holds a bachelor’s, master’s, and doctorate in entomology from the University of Michigan. He has served as WIRC director for more than 30 years, and he has taught entomology at the University of Wisconsin since 1996.
Sources
- Carnegie Museum of Natural History, “So Just What Is a Wheel Bug?“
- University of Florida Institute of Food and Agricultural Sciences, “Wheel Bug“
- Buckeye Yard and Garden Online, “Wheel Bugs Are on the Hunt: Look, but Don’t Touch!“
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