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Beware the Stinging Cats of Fall

An moth with brown and orange coloring.

With this cooler early fall weather, of the Clemson University Cooperative Extension just had to get out and do some pruning, which she typically does not do this time of year.

Patricia pruned her 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 she was almost done gathering the bundle of the wonderful wavy flower-arranging sticks, she encountered a beautiful, large caterpillar — bright green and covered with sinister-looking spines. Fortunately, she 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.

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 [email protected] or 1-888-656-9988.

Written by , Home Horticulture Agent and Master Gardener Coordinator Horticulture Program Team, Darlington County Cooperative Extension Office, Florence County Cooperative Extension Office, Clemson University.