Caterpillars
This is the one group where the danger signal is inverted: the caterpillars that sting look softer than the ones that do not. Fuzzy is not a safety cue.
5 species, each checked against a reference source. Dangerous ones first — that is the question people arrive with.
Medically significant
Everything else
Start with a photograph
Identify a caterpillar from a photo. The result includes confidence, common lookalikes and a plain safety assessment; read its accuracy and limits before treating a low-evidence photo as definitive.
Found a mark but not the animal? See why a bite cannot identify the bug.
Guides for bugs described by appearance
Reading a caterpillar
A caterpillar is a larva, so it often looks nothing like the moth or butterfly it becomes, and the adult is no help in identifying it. What matters is the surface.
- Even, uniform bristles all over — usually safe to handle.
- Tufts standing proud of the coat, fleshy horns, or spines in clusters — that is stinging apparatus.
- Smooth and green with no ornament — almost always harmless.
- Looks like a scrap of fur or cotton wool with no visible structure — that is the exception, and it is the most dangerous one.
Soft-looking does not mean safe
The puss caterpillar hides venomous spines completely beneath what looks like plain fur, and delivers one of the most painful stings of any insect in North America. Children pick them up precisely because they look strokeable. It is the single caterpillar worth learning by sight, and the reason the rule about tufts and spines has an exception attached to it.
Common questions
Which caterpillars sting?
In the US, the ones that matter are the puss caterpillar, the saddleback, the io moth and the various tussock moths. They sting on contact via hollow spines or irritating hairs rather than biting.
What do I do if I have been stung by a caterpillar?
Press adhesive tape onto the skin and pull it off to lift out broken spines, repeating with fresh tape, then wash the area and use a cold compress. Seek medical attention if the pain is severe, the swelling spreads, or the person stung is a child.
Are fuzzy caterpillars safe to touch?
Not reliably. A woolly bear is fine. A puss caterpillar looks softer and is the worst sting in the group. Look for structure in the coat rather than judging by fuzziness.