The assassin bug with a cog on its back
On June 18 in Pittsburgh, a large, grey insect was climbing a sunflower stem, and I recognized it from ten feet away. It was the wheel bug, the one insect in North America that wears a semicircular crest of teeth on its back, like a gear from a clock that has come to life. It moved in the deliberate, unhurried way of a hunter that knows nothing in the garden is faster than it is.
It was Arilus cristatus, the North American wheel bug, a member of the assassin bug family Reduviidae in the order Hemiptera. The species name cristatus means “crested,” and the crest is unmistakable: a half-wheel of small spines on the thorax that no other bug in the region has.
Assassin bugs are predators, and the wheel bug is a serious one, stabbing other insects with its curved beak and injecting saliva that dissolves the prey from the inside. In gardens it is genuinely beneficial, keeping caterpillars and other plant feeders in check. The flip side is that the same beak delivers a famously painful bite if you mishandle one, so I photographed it and kept my fingers well clear.
For an insect built like a tank, it has a delicate secret: the adults are strong fliers and sometimes turn up at porch lights, and it ranks among the largest assassin bugs in North America. A cog-toothed hunter patrolling the garden, best admired from a respectful distance. I will be watching for its nymphs next summer, tiny dark versions of the same design, already wearing a hint of the crest that will one day mark them as adults.
