I’ve been writing about gardening in the Pittsburgh Tribune-Review for about seven years, and last week my inbox was flooded with the exact same question from ten different readers: “What is this crazy insect I found in my yard?” They go on to describe the insect as “prehistoric,” “enormous,” “terrifying,” and “ugly.” Some of the emails even included pictures.
They’re all referring to the wheel bug (Arilus cristatus), and all of their descriptions are perfectly accurate.
Wheel bugs are among North America’s largest true bugs, reaching over an inch and a half in length at maturity. That’s a crazy-big bug for these parts! And not only are they huge, their body looks like it’s straight out of a sci-fi flick. Wheel bugs have half of a large “cog wheel” sticking out of their back and slender legs that make them move like some kind of insane robot. But despite their terrifying appearance, I’m here to assure you that they are very good bugs for the garden.
You see, wheel bugs are but one member of the assassin bug family (Reduviidae), a group of about two dozen different species. Gardeners most often encounter other, slightly smaller and more “normal looking” family members, including the spined assassin, the masked hunter, and several species within the Zelus genus. All assassin bugs use their bristly front legs to ambush and capture prey insects, which they then pierce with their long mouthpart. They inject the insect with a lethal toxin, killing it within seconds. The same toxin then liquefies the unlucky captive’s innards, and the assassin slurps them up like a protein shake, leaving only the empty exoskeleton behind.
Wheel bugs and other members of the assassin family, feast on lots of garden nasties, including hornworms, Mexican bean beetles, Japanese beetles, Colorado potato beetles, leafhoppers, cucumber beetles, lygus bugs, aphids and caterpillars of all sorts. Mind you, these predators aren’t overly discriminating and will capture a ladybug or two along the way, but overall they are on the right team, working to control many common pests.
In a typical year, I only come across one or two assassin bugs, and until recently, I had never even seen a wheel bug in person. But last year, I spotted no less than a half dozen wheel bugs in my yard and garden.
I think the reason wheel bugs in particular are becoming so numerous here in the eastern U.S. is because they love to feast on the brown marmorated stink bugs that have become quite prolific in our region. I even spotted a wheel bug clinging to the back of my house with a stink bug in its grasp, using its long, curved mouthpart to suck the little stinker dry.
Though wheel bugs are “good guys” in the garden, you should be aware that, if handled roughly, their mouthpart can puncture human flesh and will leave a nasty, painful welt. If you’re lucky enough to find one (or six!), leave them be and thank them for their good work on your garden’s behalf.