Friendly Assassin

Welcome the wheel bug into your garden and you won’t be sorry.

Robert Meganck

The spiny ridge that arilus cristatus sports on its back, looking rather like half a cogged wheel, makes it obvious how this insect got its common name—“wheel bug.” But if the wheel has a purpose, nobody seems to know what it might be. The “bug” part, however, is entirely straightforward. Not merely a generic synonym for “insect,” this bug is called a bug because it is a bug­­—a “true” bug, to be distinguished from bugs that apparently are not really bugs at all. (Lightning bugs, for example, are actually beetles.)

What makes these critters “true” bugs is some entomologically technical business about wings that are leathery at the base and membranous at the top, but also, and more arrestingly, the possession of a beak-like mouth-part, or proboscis. Most true bugs put their proboscises to use sucking on plants. The wheel bug’s proboscis is a vicious looking piece of business, and its business is vicious work—enough to earn it membership among a deadlier fraternity, the “assassin bugs.” As you might guess from that nickname, this bug is a predator, sitting atop the insect food chain with an ecumenical palate for everything from caterpillars to beetles to sometimes (no love lost here) each other.

I’m not sure why the Syfy cable channel, which has brought us such cinematic classics as shark-infested tornadoes (Sharknado) and giant spiders ravaging New Orleans (Arachnoquake) has failed to seize upon the horror-genre potential of the wheel bug. It is a big bug, one of the largest true bugs, growing to more than an inch. Its looks give it a sinisterly prehistoric quality (and indeed another of its nicknames is “sail back dinosaur bug”; it is part of the order Hemiptera, which dates to the Paleozoic Era). And when it dines out, it does so thus: it clutches its prey, stabs it with that proboscis, injects venomous enzymes that paralyze the victim and liquefy its innards, then proceeds to slurp up the contents like a preschooler with a juice box. This bug’s modus operandi makes Alien look like a rerun of Barney & Friends.

Even sober-minded scientists seem to hold the wheel bug in some awe. Eric Day of the Department of Entomology at Virginia Tech waxes nearly poetic in his descriptions for a Virginia Cooperative Extension publication, calling A. cristatus a “‘monster’ of the insect world” with a “deadly beak” that makes it the “dreaded foe of other insects.”

On the other hand, Day is also quick to point out that, “Yikes!” factor aside, the wheel bug, for its predatory habits, is a welcome addition to your garden, your friend and ally in pest control. While its presence is considered a good sign of a healthy garden ecosystem, you might have to look hard to spot any at work among your plants. Generally a shy and non-aggressive insect (unless you have the misfortune of being a passing caterpillar, say, or beetle), the wheel bug is well camouflaged in bark- and leaf-litter shades of brownish-gray, and would prefer to avoid your company.

Be warned: It does not take kindly to handling. Pick one up, and you might find yourself proboscisedly pierced. No, your insides won’t be liquefied, but that fact may prove small consolation while you suffer pain variously described as “worse than a hornet’s sting,” “worse than childbirth,” and “worse than being shot.” The wheel bug’s venom is a neurotoxin, and while, except for the rare allergic reaction, the actual harm caused is generally localized to a small and sometimes slow-healing wound, the agony, one gathers, is memorable.

The wheel bug’s ferocity is belied by a certain gracelessness. On foot, these bugs are slow-moving, and in the air, they are bumbling, buzzing, short-distance flyers. They might seem like easy prey themselves, therefore, but beyond the proboscis, the wheel bug has other defensive weapons in its arsenal. It is possessed of a pair of scent glands that can emit an unpleasantly pungent stench; one theory about the wheel bug’s wheel is that it serves to warn potential predators that, with a taste as bad as its smell, the wheel bug is not a delightful, crunchy snack but rather a mouthful of nasty.

In this quality, the wheel bug resembles its even more odiferous cousin the stink bug, but in the “no accounting for taste” department, we can celebrate the news that, stench be damned, the wheel bug has apparently developed an appetite for that utterly noxious invasive, the Asian brown marmorated stink bug. This past fall, The New York Times noted that the wheel bug population seems to be enjoying a significant boost from the culinary bounty of these non-native stink bugs which, according to the University of Maryland entomologist Michael J. Raupp who is quoted in the article, “are higher in protein and lower in fat than a steak.”  

And so I believe I speak for myself and every other stink-bug plagued farmer, homeowner and gardener in the Commonwealth when I offer to our native, wheel-sporting assassin a hearty wish: Bon appétit.

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