The World Conservation Union ranks the gypsy moth, Lymantria dispar, on its list of "100 of the World's Most Invasive Alien Species." If you live in the northeastern U.S., you will heartily agree with that characterization of this tussock moth. Accidentally introduced to the U.S. in the late 1860's, the gypsy moth now consumes a million acres of forest each year, on average. A little knowledge about this insect goes a long way toward containing its spread.
Gypsy moth adults, with somewhat drab coloring, may escape notice unless they are present in large numbers. Males are capable of flight, and fly from tree to tree looking for mates among the flightless females. Sex pheremones guide the males, who use large, plumous antennae to sense the chemical scent of females. Males are light brown with wavy markings on their wings; females are white with similar wavy markings.
Egg masses appear buff colored, and are laid on the bark of trees or other surfaces where the adults have pupated. Since the female cannot fly, she lays her eggs close to the spot where she emerged from her pupal case. The female covers the egg mass with hairs from her body to insulate it from the winter cold. Egg masses laid on firewood or vehicles add to the difficulty of containing the invasive gypsy moth.
Caterpillars emerge from their egg cases in spring, just as tree leaves are opening. The gypsy moth caterpillar, like other tussock moths, is covered in long hairs giving it a fuzzy appearance. Its body is gray, but the key to identifying a caterpillar as a gypsy moth lies in the dots along its back. A late stage caterpillar develops pairs of blue and red dots - usually 5 pairs of blue dots in the front, followed by 6 pairs of red dots.
Newly emerged larvae crawl to the ends of branches and hang from silk threads, letting the wind carry them to other trees. Most travel up to 150 feet on the breeze, but some can go as far as a mile, making control of gypsy moth populations a challenge. Early stage caterpillars feed near the tops of trees during the night. When the sun comes up, the caterpillars will descend and find shelter under leaves and branches. Later stage caterpillars will feed on lower branches, and may be observed crawling to new trees as defoliation spreads.
Gypsy moth caterpillars feed on a huge number of host tree species, making them a serious threat to our forests. Their preferred foods are the leaves of oaks and aspens. Adult gypsy moths do not feed.
The gypsy moth undergoes complete metamorphosis in four stages - egg, larva, pupa, and adult.
Egg - Eggs are laid in masses in late summer and early fall. Gypsy moths overwinter in the egg cases.
Larva - Larvae develop within their egg cases in the fall, but remain inside in a state of diapause until spring when food is available. The larvae go through 5-6 instars, and feed for 6-8 weeks.
Pupa - Pupation typically occurs within the crevices of bark, but pupal cases may also be found on cars, houses, and other manmade structures.
Adult - Adults emerge in two weeks. After mating and laying eggs, the adults die.
Special Adaptations and Defenses:
Hairy tussock moth caterpillars, including the gypsy moth, can irritate the skin when handled. The caterpillars can spin a silk thread, which helps them disperse from tree to tree on the wind.
Hardwood forests in temperate climates.
The gypsy moth has been spotted in nearly every state in the U.S., though populations are heaviest in the northeast and Great Lakes region. The native range of Lymantri dispar is Europe, Asia, and North Africa.
Other Common Names:
European Gypsy Moth, Asian Gypsy Moth (Note: the Asian Gypsy Moth is actually a strain of Lymantria dispar native to Russia.)
- Gypsy Moth in North America, US Department of Agriculture
- Garden Insects of North America, by Whitney Cranshaw