Salt marsh caterpillars are larvae of a moth in the Family Arctiidae. This species has many color variations from black with orangish-red markings to pale yellow to reddish-brown. Caterpillars are generally lighter in color and darken with age. The body is covered with tufted hairs, or setae.
Some people also commonly call these caterpillars woolly bear caterpillars (there are numerous species of moths that can be called woolly bears). The caterpillars are often called woolly bears because of the numerous bristly hairs that project off the body.
The caterpillars are generalists and feed on broad-leafed plants. They usually feed as a group when they are young, but as they grow older and larger they tend to disperse. As they become full grown, they begin to wander away from the host plant to find a protected site where they can spin a cocoon.
Populations of salt marsh caterpillars are typically highest in the fall and are often seen in large numbers wandering across driveways or roadways. Wandering may be to find other food sources when old sources are consumed or it could be caterpillars in search of a protected place to pupate.
The stinging capability or irritation that hairs may cause seems to be in debate in entomological circles. Some entomologists claim that woolly bears can sting you or irritate your skin while others say that they cannot. I think that it probably comes down to skin sensitivity. While I haven’t had problems handling woolly bears, it doesn’t mean that everyone has no reaction; others may have sensitivity to the caterpillar hairs. Basically the take home lesson is to always be careful when handling a wild animal since you never can predict what may happen.