Keep your eyes peeled for adult Wheel Bugs (Arilus cristatus, family Reduviidae) if you’re working among the branches of landscape trees and shrubs. The bugs are highly beneficial. They use their piercing-sucking mouthparts to extract the essence-of-insect from soft-bodied prey such as caterpillars and sawfly larvae. However, they may occasionally use their insecticidal equipment to deliver painful bites to people.
During a videotaping, last Friday in Loveland, OH., Kayla Perry (Forest Entomology, OSU Entomology) spotted an adult Wheel Bug (Arilus cristatus, family Reduviidae) skulking about within the branches of a boxwood. The video subject was Box Tree Moth (BTM) (Cydalima perspectalis, family Crambidae) and we had just finished using our hands to part the boxwood branches to look for BTM caterpillars. We were lucky.
This is the time of the year when adult wheel bugs roam Ohio’s landscapes and forests in search of a meat meal. The immatures (= nymphs) have been with us for some time lurking among the leaves of trees and shrubs on the hunt for soft-bodied insects.
Wheel bug adults are big, measuring over 1 1/4" long, and their color ranges from blackish-gray to bluish-gray to grayish-brown. The “wheel” in the bug’s common name only appears on adults and refers to the peculiar morphological feature that rises from the top of the adult bug's pronotum which is the first thoracic segment behind the head. The distinctive structure looks like half of a cogwheel, with the gear teeth clearly visible.
Wheel bug nymphs look nothing like the adults. They hold their curved abdomens upright as they parade around on their long, spindly, spider-like legs. In fact, the nymphs are commonly mistaken for spiders. We normally don’t see the big adults lumbering around in groups. However, it’s common to find several nymphs patrolling the same branch of a tree or shrub in search of prey.
Insects that belong to the heteropteran family Reduviidae are collectively known as Assassin Bugs. The family includes over 190 species in North America, and almost all are so-called “ambush predators” meaning they sneak up on their prey. The common name for the family clearly describes how these stealthy hunters make a living and wheel bugs serve as an ideal poster child for assassin bugs.
Wheel bugs and other family members sport three obvious features that support their predatory lifestyle. They have large, bulbous eyes: "The better to see you with, my dear." Their raptorial front legs are designed for grabbing and holding prey in death's embrace.
Their piercing-sucking mouthparts are housed in a structure called a beak: "The better to eat you with." It swings into action (literally) to inject paralyzing and pre-digestive enzymes into prey which is most often another insect. Like miniature vampires, they then suck the life from their hapless victims.
Caterpillars and sawfly larvae are the favored table fare of these voracious predators. Indeed, Kayla and I believed that it was no accident the wheel bug was creeping among the branches of a BTM caterpillar meat buffet.
Of course, wheel bugs will not turn their beaks up at other arthropod meat morsels. They will feast on just about anything they can wrap their raptorial front legs around. As noted above, they will even nail the probing fingers of uninformed gardeners or perhaps unlucky entomologists!
Over the years, I’ve had a few wheel bug adults march quickly in determined strides towards my fingers as I took their picture. I’ve never been certain if they were aggressively defending their space, which is something predators of all sizes will do, or if they perceived my fingers as big, juicy caterpillars. Either way, their move usually ended with me making an undignified cri de coeur as the bug suffered the pull of gravity.
All members of the assassin bug family are capable of delivering a painful bite to people. The pain of a bug bite has been described as being equal to or more powerful than a hornet sting, and the wound may take over a week to heal. These beneficial insects should not be handled but appreciated from afar.
Kissing Cousin Confusion
Unfortunately, wheel bugs may be misidentified as Kissing Bugs (family Reduviidae, subfamily Triatominae). This can create concerns because kissing bugs elsewhere in the world vector the protozoan parasite, Trypanosoma cruzi, which is the pathogen behind Chagas disease.
Adding to the confusion, Ohio is home to a native kissing bug with a horrible-sounding common name, the Bloodsucking Conenose (Triatoma sanguisuga). However, the conenose remains rare while wheel bugs are common in Ohio landscapes at this time of the year.
Thankfully, the bloodsucking conenose focuses its blood-sucking attention on small animals rather than humans. Equally important, Chagas disease is not endemic to Ohio. So, we don’t have infected people providing a reservoir for the pathogenic protozoan that causes the disease.
I have been taking pictures of our native kissing bug since 2010. Each year, I’ve received reports verified with photographs of the bloodsucking conenose finding its way into Ohio homes.
Thus far, the homes have been located in prime habitats for small animals such as in or near wooded or unmowed naturalized areas. Occasionally, there has been compelling evidence of people being bitten by a kissing bug. However, I’ve been unable to find any reports of Chagas disease developing from kissing bug bites that occurred in Ohio.
Identification errors between wheel bugs and the conenose are understandable given that they both belong to the insect taxonomic order, Hemiptera. “Hemi-“ means “half,” and “ptera” means “wing.” If you look closely at the front wings of kissing bugs and wheel bugs, only the back half of their wings are membranous, so it looks like they only have half of a wing.
Of course, the wheel bug and bloodsucking conenose also belong to the assassin bug family, Reduviidae. So, they both share family traits such as long spindly legs, and narrow heads with beady eyes. Also, they are relatively large insects with the conenose only being slightly shorter in length compared to the wheel bug.
However, no kissing bug species has a wheel-like structure rising from their thoracic pronotum. Wheel bugs don’t have reds spots on the upper edge of their abdomens.