The salt-marsh caterpillar is better known by one of its other common names, woollybear or woollyworm. This caterpillar is found throughout the United States and feeds on many weeds and grasses. It is found in vegetable fields and gardens, pastures, meadows and on many ornamental plants. Adults of the salt-marsh caterpillar have a wingspread of about two inches. Their front wings are milk-white. The hind wings of the female are milk-white but in the male they are yellow-orange. Both front and hind wings have numerous black spots and appear as if they have been "peppered". The front part of their body, the head and thorax, is white. The back part, or abdomen, is yellow-orange with a white tip and seven black spots running down the middle of the top. The males are a bit smaller than the females.

Full grown caterpillars are about two to two and one half inches long. They have a reddish-brown body that may be difficult to see because of the long black hairs that cover the entire body. Salt-marsh caterpillars spend the winter as full-grown larvae, hidden away in protected places. In the spring they pupate inside a silk cocoon that is interwoven with the long hairs from their body.

Females may lay as many as 1,000 eggs each. They are placed in masses on the under side of leaves. Feeding activity of these caterpillars result in irregularly shaped holes in plant leaves. When populations are large feeding can result in considerable damage.

When disturbed the caterpillars often curl up and play dead. They may often be seen crawling rapidly across the ground, roads or lawns, as if they were in a big hurry to get somewhere. They are often seen in very large numbers, migrating across roads or landscape. Salt-marsh caterpillars do not sting or bite and are often handled as if they were pets. However, they should be handled with care as some people may be sensitive to the long hairs on their body.