American Dagger Moth (Acronicta americana) caterpillars are present from June to October in the Northeast, but because of their size (up to 2 ½”) and their searching for a suitable site to pupate in over the winter, they are very evident right now.
American Dagger Moth caterpillars have lemon yellow (early instars) or white (late instars) setae, or hairs. Their distinctive characteristic is the pattern of black tufts: two pairs of diverging tufts along the middle of the caterpillar and one thick black tuft at the end. As larvae they have a wide variety of host trees, including alders, ashes, birches, elms, hickories, maples, oaks, poplars, walnuts, and willows.
After locating a wintering site, these caterpillars will spin a cocoon in which they will spend the next several months as pupae. Late next spring American Dagger Moths will emerge from their cocoons as two-inch-long brown moths.
If touched, these caterpillars can cause a mild allergic reaction (a rash) in some people who touch the them.