The gypsy moth, Lymantria dispar, was introduced to the U.S. in 1869 and has since become a serious pest in the northeastern part of the country. In some areas, it has changed the ecology of native forests, defoliating more than 13 million acres of woodlands in one season.

The invasion has moved westward, with established populations in Michigan, Wisconsin, Indiana and Illinois. They are generalist feeders, happily devouring more than 450 species of plants. Oaks are the preferred host, but they also feed on alder, apple, aspen, beech, birch, black gum, cherry, hawthorn, hemlock, hornbeam, larch, linden, maple, pine, sassafras, and spruce. Trees showing the most resistance include ash, balsam fir, butternut, black walnut, catalpa, red cedar, dogwood, holly, locust, sycamore, and tulip tree.

The young, tiny larvae (caterpillars) do most of the damage. The caterpillars spin a silken thread suspended from a leaf, where winds disperse the larvae several hundred feet, spreading the population.

Source: The Morton Arboretum

Gypsy moth caterpillars are a shade tree pest in the Northeast and Midwest.
TOP: Male, female (l-r) moth BOTTOM: Wasp laying eggs on moth pupa
Scott Bauer, USDA ARS, Bugwood.org; Pennsylvania Department of Conservation and Natural Resources – Forestry, Bugwood.org; USDA APHIS PPQ; John Ghent, Bugwood.org.