Ennomos subsignaria

The elm spanworm has a misleading common name since elm is not the only host of this insect that, on occasion, has historically been known to occur in outbreak populations that defoliate thousands of acres of hardwood forests. Caterpillars of this species are generalist feeders that are known to the eastern United States and Canada. Young larvae feed on the lower leaf surface of host plant leaves, creating perforations or shot hole-like damage. They feed on young leaves as they are maturing, eating most of the leaf except for the midrib and petiole. Caterpillar activity may begin in mid-late May. The body of the caterpillar may be a dull black color and the head rust-colored. Some caterpillars may be light green with yellow head capsules. In low population years, a higher proportion of lighter colored larvae are usually reported. Caterpillars develop over approximately one month (reaching up to 2 inches in length when mature) and pupate in net-like cocoons that they attach to the partially eaten leaves of their host plants. Pupae are light brown in color. Adult moths (1 to 1.5 inch wingspan) appear in late-July or August and are bright white in color. Females lay clusters of 250 eggs on the undersides of twigs, large branches, and tree trunks, where they will overwinter. Freshly laid eggs are a bright green-yellow but over time (by winter) turn a dull gray/brown color. Adult moths are attracted to outdoor lights at night.