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Excerpts from Jim Conrad's
Naturalist Newsletter
from the June 17, 2012 Newsletter issued from the woods of the Loess Hill Region a few miles east of Natchez, Mississippi, USA
SPINY IO MOTH CATERPILLARS
How often have I embarked on long fieldtrips only for the best discovery of the trip to turn up right outside my door? That happened last weekend. As I stepped off the porch leaving for a 20-mile bike ride into the bottomlands, within arm's length, on the underside of a Sugarberry leaf, there was what's shown above. A single caterpillar appears below.
Volunteer identifier Bea in Ontario pegs these as caterpillars of the Io Moth, AUTOMERIS IO. Therefore, the 1½-inch-long (4cm) larvae in the photo are intermediate-stage instars -- partway through their several molting stages -- because Io Moth caterpillars reach 2¾ inches long (7cm) before metamorphosing. While the caterpillars are solitary during their later instars, they are gregarious in the early ones.
Io Moth caterpillars are known to eat many kinds of vegetation, including birches, clover, corn, maples, oaks, willows, roses, palms, grasses, and elms. Our Sugarberry trees are a kind of hackberry in the Elm Family. You might guess that a species capable of such omnivory might enjoy a large area of distribution, and that's the case: They're common throughout eastern North America west to Arizona and south through Mexico into Central America.
Sometime caterpillars' sharp-looking spines are perfectly harmless, but Io Moth caterpillar spines can "sting," and the larger the individual, the worse the sting. Stinging hairs are technically known as "urticating spines."
The caterpillar's spininess seems to account for the species' name, Io. In Greek mythology Io was a nymph seduced by Zeus, who changed her into a heifer to escape detection. But Hera, Zeus's wife, found out about the arrangement and sent a maddening gadfly to torture Io. The gadfly's bitefulness apparently was remembered by the namer of the Io Moth, with its caterpillar's stinging hairs.