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. Caterpillars of Orgyia definita are readily identified by the yellow color of the head, prothoracic plate and dorsal glands. The hair pencils are less fully developed than in the other species. The hair on the body is entirely whitish and the verrucae (the wart-like structures along the body) are pale yellow.
Deciduous forests and orchards.
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. Larvae feed on apple, ash, basswood, birches, boxelder, cherry, elm, maple, oaks and willows. CAUTION: the hairs of caterpillars in this genus are known to cause skin irritation.