Harmless. It does not sting. The bristles are stiff rather than venomous and at worst feel prickly. This is the fuzzy caterpillar it is safe to let walk across your hand.
Size30–50 mm long
MarkingsBlack at both ends with a rust-brown band across the middle · Dense, even, bristly coat — no tufts, horns or spines standing out
WhereAcross North America, in grass, gardens and along paths.
SeasonMost visible in autumn as it looks for somewhere to overwinter
What it is not
A woolly bear is most often confused with a species that is medically significant. If you are trying to rule those out, check these:
Black at both ends with a rust-brown band across the middle
Dense, even, bristly coat — no tufts, horns or spines standing out
Curls into a tight ball when picked up
Often seen crossing paths and roads in autumn
Where you’ll find it
Across the whole of North America, from the Gulf states up into Canada. It is one of the few caterpillars almost everyone has seen.
Across North America, in grass, gardens and along paths.
Most visible in autumn as it looks for somewhere to overwinter.
How it behaves
In autumn it leaves its foodplant and walks, sometimes for surprising distances, looking for somewhere to overwinter. That is why it turns up crossing paths and roads and why it is the caterpillar people most often pick up. It survives winter frozen solid under leaf litter or a log, pupates in spring, and emerges as the Isabella tiger moth.
You’ve found one indoors
Let it walk. If it is crossing a road you can move it to the verge in the direction it was already heading. It needs leaf litter and undisturbed corners to overwinter, so leaving some of the garden untidied does more for it than anything else.
Common questions
Can a woolly bear predict the winter?
No. The folklore says a wider brown band means a milder winter. The band actually reflects the caterpillar age and how the season has gone so far — it is a record of the past, not a forecast.
Do woolly bears sting?
No. The bristles are stiff rather than venomous. Very sensitive skin can react mildly to the hairs, but there is no sting and no venom.
What does it turn into?
The Isabella tiger moth — a plain yellowish-orange moth that is far less famous than its caterpillar.
It curled into a ball when I picked it up. Is it hurt?
No, that is its whole defence. It curls up and relies on the bristles making it unpleasant to swallow. Put it down and it will uncurl and walk off.
naturalist charlie · CC-BY