Science
Illinois Caterpillar Watch Today: Which Fall Species Can Sting?
Springfield, IL – Illinois residents may be noticing some unusually large, colorful or fuzzy caterpillars crawling across decks, trees, sidewalks and yards as fall gets underway — and some are much sa
By Rachel Monroe · 2026-09-29T06:03:04.800Z
Springfield, IL – Illinois residents may be noticing some unusually large, colorful or fuzzy caterpillars crawling across decks, trees, sidewalks and yards as fall gets underway — and some are much safer to touch than others.
According to University of Illinois Extension , caterpillars seen during late summer and fall include the larvae of butterflies and moths, with some mature caterpillars leaving their food plants as they search for places to pupate or spend the winter.
The bright green caterpillar pictured with this story appears consistent with a polyphemus moth caterpillar , one of Illinois’ large native silk moths. Mature polyphemus caterpillars can grow several inches long and are typically bright green with pale diagonal markings and small bumps carrying sparse hairs. They do not have venomous stinging spines .
Other large silk moth caterpillars, including cecropia and luna moth caterpillars , may also turn up around Illinois in late summer and early fall. These impressive green caterpillars are not considered stinging species.
One of the most recognizable fall travelers is the woolly bear caterpillar , with bands of black and rusty brown hairs. Woolly bears do not sting, although their stiff hairs can irritate sensitive skin.
There are caterpillars residents should avoid handling.
Saddleback caterpillars have a distinctive green “saddle” marking surrounded by brown and carry venomous spines capable of producing immediate burning or pain. Io moth caterpillars are bright green with clusters of branching spines that can also sting.
Hairy caterpillars such as the hickory tussock moth caterpillar can cause skin irritation when their hairs become embedded in the skin.
The safest rule is simple: admire unfamiliar caterpillars without picking them up, especially if they have obvious spines or dense hairs.
As cooler nights arrive, sightings may increase temporarily as mature caterpillars wander away from trees and plants looking for protected places to complete the next stage of their life cycle.