The elusive, magnificent wheel bug

I spent a good 15 minutes digging up winter creeper vines before I noticed one of the hundreds of bumblebees buzzing around the Canada goldenrod near my head was oddly swaying back and forth in a strange sideways position. I stopped to look at the strange bumblebee, saw the un-mistakable spiked ridge on the back of the insect eating it and dropped my shovel. Finally, a wheel bug!


When I took an entomology class last fall our semester project was to create, label, and display an insect collection featuring 100 unique evolutionary families. Our professor went to great lengths to communicate how feasible this project would be for us. On the first day I met with him about joining the class he assured me I could complete my collection in one night at any city porch light with a butterfly net and collecting jar, something that was technically probably true although it would have required a certain skill level in curating and species IDing. The rest of the semester he settled for pointing out species during his lectures that he was sure we all had in our collections. His fall back species was the wheel bug. By count of his in-class mentions I should have had about 10 wheel bugs by the time several hard freezes put a lid on insect collecting for the year. Alas, I found none. I grew so frustrated by constantly hearing about wheel bugs I started to search for them exclusively, and inevitably to doubt their existence as a common urban insect. To be honest, part of me doubted them from the beginning. The wheel bug doesn’t look like something you’d find in a city. It looks too wild, like some tropical terror of the night.

Fast forward a year and just as the flowering of the Canada goldenrod signals the onset of fall so here was a wheel bug injecting paralyzing salival enzymes into a bumblebee just a few inches from my head. The wheel bug, species name Arilus cristatus, is the largest member of the assassin bug family Reduviidae of the true bug order Hemiptera. Still, I was truly stunned by the size of the wheel bug in person. A large beetle or moth probably has just as much mass but everything on the wheel bug felt oversized. The flattened, plated abdomen, the lanky forelegs, the protruding beak-like proboscis and the long antennae slowly going round and round, but mostly that great thoraxian wheel rearing up behind its head like a Roman war helmet. Also, it was eating a bumblebee. Yes bumblebees are unaggressive but I still remember how they terrified me as a child and really, what insect eats a bee that big?

bee tongue

Who knew bees had such long tongues! And that they often stick those tongues out as they die. I always find one of the most bizarre features of insect collections to be the rows of dopey looking long-dead bees with tongues in different stages of hanging out of their heads.

Watching the wheel bug I went from being impressed it had killed a bumblebee to amazed it had caught it in the first place. When I first noticed them the wheel bug had its long proboscis injected into the bee’s underbelly. As I sat watching it withdrew its beak, deftly rotated the bee with its forelegs, and successively inserted its proboscis in just about every part of that poor bee. This wheel bug was certainly nimble with its forelegs but nothing about its movements suggested quickness, certainly not the kind needed to catch bees. Its movements were jerky, lurching. The wheel bug is a sit and wait predator along the lines of the praying mantis. And how long, I wonder, did it sit on that goldenrod until one bee came just close enough? Quick conclusions based off observation of body morphology suggest the wheel bug trails the mantis in foreleg catching power but has an overwhelming edge when it comes time to eat what’s been caught, unfolding its long proboscis from a groove under its head and driving it into soft folds in its prey. The “bite” of the wheel bug, really more of a stab, contains enzymes which rapidly immobilize small insect prey and then “digest” the prey’s insides. The wheel bug, lacking chewing mouthparts, basically just sucks it all out. People studying them in the lab have reported accumulated piles of dried-up, hollowed out carcasses beneath feeding stations.

Which brings us to wheel bug-human interactions. Turns out this is a case where the looks match the bite! Those digestive enzymes? They get injected into your thumb just as readily as into a bee. I take logarithmic pain scales with a grain of salt but the internet consensus for a wheel bug bite seems to be 10 times the pain of a wasp or bee sting. Yikes! I feel compelled to mention this only adds wheel bugs to the endless list of potentially harm-causing animals that in reality would rather do anything with their day than waste a sting or a bite on a human that is very, very much not on their menu. I’ve been walking, working, and as a child rolling around in grassy fields for years and far from being bitten by one had never even noticed a wheel bug until now.

At this point a physical description of the wheel bug that includes some identifying features would usually be in order. I’m not sure words can add much to a picture of this distinctive species. Nothing in North America looks anything like it. A great article covering the biology and life history of the wheel bug is “Inventing the Wheel(bug)” from a great blog by an Ohio-hailing, University of Arkansas graduate student in entomology. He begins by keeping a breeding pair captive for the summer and includes a memorable review of the scientific literature for the most morbid descriptions of their feeding habits. As for me, I’m tickled to find more things eating each other in the yard. Plus I now have two more things to keep an eye out for: the wheel bug’s honeycomb-like egg clusters and then in the spring the hatched nymphs. They look like ants with extra-long legs walking around with their back ends, round red bulbous things, stuck up in the air.

wheel flexing

The wheel mechanism occurs on both males and females and no one has yet found a good explanation for its use. It’s attached to the thorax, which is the insect’s second segment, behind the head. Knowing this I shouldn’t have been surprised when the wheel flexed away from the abdomen as the wheel bug changed position, but I still found it strange. It’s such a large and bizarre feature it was strange for it to flex so naturally along with the rest of the body.

I noticed this phenomenal specimen and slice of the food chain while out working, digging, as I mentioned, winter creeper. Not every work night is so fruitful. Most nights I work until it becomes too dark to see or more often until I let one of my breaks sitting on a tree stump go on too long and my muscles cool down and it just feels like time to go inside. But, I also would have never found this wheel bug had I not had work to do. For me the greatest challenge of the urban wilderness is that it comes with the rhythm of the city, so easy to stay inside, to turn on the television, or lose track of daylight time while working under electric lights. So many wonderful things come from labor but I try to make the work an end in itself. When you lose yourself in the digging, the dragging, and the grubbing, sometimes that’s when unusual things start to jump out at you and when your brain, flushed with the headiness of physical labor, is ready to receive the clarity of new information. When I have worked up a light sweat, humbled my fingernails with some soil, and worked the tension out of stiff muscles, only then do I begin to feel the comradery that we are blessed with as participants in the living world. Indeed, in this case I had just noticed my digging in the winter creeper was going to rip up the stand of goldenrods and I’d begun to dig them out to be moved. “Wheel bug! You thought that was the wind swaying your goldenrod flower perch in the October evening air? Nay, that was my shovel you were feeling.” I left the Canada goldenrods where they were. There will be other days for grubbing winter creeper, and other evenings for transplanting goldenrods. This evening was the wheel bug’s.


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