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Beware the Stinging Cats of Fall

With this cooler early fall weather, I just had to get out and do some pruning, which I typically do not do this time of year. I pruned my Curly Willow (Salix matsudana ‘Tortuosa’), a tree with curly, tortuous stems perfect for flower arrangements.

You might ask, “Why do we not prune trees and shrubs in the fall?” Because woody plants will soon be going dormant for the winter, pruning now encourages new growth, which is tender and easily injured if we get an early frost.

When I was almost done gathering my bundle of the wonderful wavy flower-arranging sticks, I encountered a beautiful, large caterpillar — bright green and covered with sinister-looking spines. Fortunately, I saw it first before being stung by the larva of the Io Moth (pronounced “Eye-oh”), which is a large, beautiful yellow/gold moth with huge eyespots on its wings.

The larva of the Io Moth is the largest stinging caterpillar commonly encountered in South Carolina. Trish DeHond, ©2020, Clemson Extension.

The larva of the Io Moth is the largest stinging caterpillar commonly encountered in South Carolina.
Trish DeHond, ©2020, Clemson Extension.

Adult io moth (Automeris io). Jessica Louque Smithers Viscient, Bugwood.org

Adult io moth (Automeris io).
Jessica Louque Smithers Viscient, Bugwood.org

Sometimes called “cats” by entomologists/insect experts, caterpillars are the immature stages of butterflies and moths. Several species of stinging caterpillars start showing up this time of year. Some are covered with pointed or barbed hairs or spines for defense against predators. Others look fuzzy and cute, or brightly colored. So, please be careful when doing any yard work in the fall around trees and shrubs. These caterpillars’ interesting appearance may hide a painful surprise if you bump into them accidentally, as they hang out on a stem or the underside of a leaf. A pretty nasty (but temporary) rash or painful raised bumps can result.

Most stinging caterpillars belong to three groups: Puss Caterpillars, Slug Caterpillars, and Giant Silkworm Moths (like the Io Moth). Usually, they are solitary, quietly feeding on the leaves of smooth-leafed shrubs and trees.

Caterpillars usually accidentally sting people when they brush against them on trees and shrubs while doing yard work. To prevent stings, be aware, and avoid them. And enjoy the cooler weather, admire cute, fuzzy caterpillars from afar, and walk away with a pleasant memory, not a burning irritation.

For an excellent fact sheet on Stinging Caterpillars, from the Clemson Extension Home and Garden Information Center, see HGIC 2482, Stinging Caterpillars.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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