Photo: Forestry Archive, Pennsylvania Dept. of Conservation and Natural Resources, Bugwood.org
The Definite-marked Tussock Moth, Orgyia definita, has a common name almost as long as the caterpillar. Some refer to the species as the Yellow-headed Tussock, which is a more descriptive name for the larva. In fact, it's more than the caterpillar's head that is yellow - its tufts of toothbrush-like hairs are a striking yellow as well.
Whatever the name they are given, these caterpillars feast on birches, oaks, maples, and basswoods throughout the eastern states in the U.S. Moths emerge from cocoons in late summer or early fall, when they mate and deposit their eggs in masses. The females will cover the egg masses with hairs from her body. Definite-marked Tussock Moths overwinter in the egg form. New caterpillars hatch in spring when food is available again. Through most of its range, the Definite-marked Tussock Moth has one generation per year, but in the southernmost areas of its reach, it may produce two generations.