The gypsy moth is one of the worst insect pests for hardwood trees in the eastern United States. It was accidentally brought from Europe to Massachusetts in 1869.

Gypsy moth caterpillars damage forests by eating all the leaves (defoliating) a tree. This stresses the tree, making it easy for other diseases to kill it. They eat hundreds of different plants, but their favorite food is the oak tree.

The first major leaf-eating event (defoliation) in West Virginia was in 1985. By 2003, gypsy moths had defoliated over two million acres of forest in the state, which has tried to stop the spread using quarantines and spraying large areas of timberland. The Division of Forestry still considers the gypsy moth the most destructive forest pest in West Virginia, with the heaviest populations found across the eastern and northern counties.