Introducing Arilus cristatus

When trying to study the natural history of North Texas, always pay attention to annual patterns to be sure, but don’t be afraid to note longer patterns. Many plants and animals here don’t obligingly make themselves visible every single year: many disappear for a year or two, and then suddenly they’re everywhere as if they’ve never left. With many others, they never left, but they suddenly become prominent for inscrutable reasons. We’re already famous for our various floods of grasshoppers and crickets, and a few are lucky enough to witness the sudden explosion of tiger beetles, mantises, or tarantulas in geographically tight areas. This year, my own personal surprise was seeing the return of the ambush bug Arilus cristatus, generally known locally as the “wheel bug”. I’ve looked high and low since coming across my first one in a tree in the summer of 2000, and haven’t seen a single one until this past week. In that week, though, I’ve encountered four of them, including this dying specimen here, and I fully expect to find even more camping out among the pineapples and Bhut Jolokia peppers in my smaller greenhouse, feeding on anything they can catch.

Looking at one from the side, it’s easy to see where the “wheel bug” name came from. In this specimen, the individual teeth in the crest are damaged in the center, but most look as if someone stuck a watch gear into its back. (Yes, I’m also glad that nobody’s calling it a “steampunk bug“. Yet.) Incidentally, for those without a Latin background, that crest is also where A. cristatus gets its species name. According to some authorities, this crest may be an identifier for birds and other predators that the wheel bug tastes as badly as it smells: in that regard, it shares with its true bug kin a very recognizable and extremely unpleasant metallic stink when disturbed.

Not that the stink is all that wheel bugs have for protection. Unlike their cousins the stink bugs, ambush bugs are all very aggressive predators (including the ones that live in symbiosis with the South African carnivorous plants Roridula spp.), so their beaks are designed to pierce flesh and carapace. If you want to know about the pain of a wheel bug bite, or the subsequent healing process, please feel free to check with someone else, because I haven’t been bitten yet nor do I plan to do so. Avoiding contact with ambush bugs is generally a good idea, whether in real life or in fiction.

Taking a look from above, A. cristatus can fly. In fact, it’s a remarkably good flier, even if it doesn’t have particular speed or agility. Swat at one, and it’s much more likely to take off and buzz away rather than risk being damaged. Not that this happens all that often anyway: wheel bugs both have excellent camouflage when against tree bark or reflective leaves (in my recent experience, they’re particularly fond of camping out in both pineapple plants and on live oaks), and they tend to hide in plain sight and attack unwary prey. During the summer, though, they’re just as likely to track prey underneath street lights, and that’s when the big ones come out. Just last Saturday, while running late-night errands, I came very close to accidentally stepping on one that was as long as my thumb.

Another thing to note about A. cristatus is the bend in each antenna. That isn’t damage or a deformity: the upper half can wave back and forth at the end of the lower half, like a cat toy. I don’t know if wheel bugs use these to attract prey, like the caudal lure on immature copperhead snakes, or if the waving helps as camouflage, but this might be a useful experiment.

And with closeup photos, the wheel bug just keeps getting better. On the lower right corner, you can see the two clawed toes on each foot, obviously used for climbing and for hanging onto prey. The head is to the left, with the eye and beak being particularly noticeable. Also note the fuzziness in the photo, because that isn’t from the camera focus. While barely visible to the naked eye, wheel bugs are covered with very fine hairs, and these grow thick enough along the legs and underside of the body that it’s easy to believe that the problem lies with the camera than with the bug. Another experiment, for this evening, is to see if these hairs fluoresce under ultraviolet light, or if they actually absorb UV and make the bug blend into its surroundings even further. Lots of ideas, and nowhere near enough time, so here’s hoping that we see more of these guys over the remainder of the summer.