Article for WES, Wisconsin Entomological Society Oct 2015 by Linda W. Curtis
One of my friends is an emergency room nurse at the local hospital. I asked her if she knew of any insect-cause problems and she answer, “Oh yes! Why, just this week…” and related an incident of someone sitting on a caterpillar with stinging hairs. Not life threatening, but certainly uncomfortable and embarrassing to explain why he preferred standing to sitting for a few days.
Turns out, I discover the culprit, a saddleback caterpillar, Acharia stimuli on a twig and carried it home to image under the digital microscope. Than an information search revealed that the stiff hairs were natural hypodermic needles with venom glands at the base. Stinging hairs are one thing, while poisonous hairs are another and a serious rash and nausea can follow.
Mimicry works for caterpillars with spines or brists even if they are not harmful because predators avoid them. For instance, the buckeye caterpillar, Junonia coenia, looks menacing, but is not. The adult butterfly stage also has a “startle effect” with eyespots on the wings.
On the other hand, the saddleback caterpillar has a rather ordinary gray-winged adult mouth the serves as camouflage, blending it into the tree trunk texture. That function is more “not seen, not eaten” instead of “watch out!”
Linda W. Curtis