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Gypsy Moth (Lymantria dispar)
Gypsy moth: a pest of trees
male gypsy moth
Male Gypsy moth
Gypsy moth (GM) caterpillars have defoliated millions of acres of trees and shrubs in the northeastern United States. Since the late 1970's, small isolated populations of this insect have been detected and eradicated in Oregon.

GM established in the U.S.
map of movement
Map of movement
How did gypsy moths get to the U.S.?
A naturalist first brought the gypsy moth into Massachusetts from Europe in 1869 to develop a disease-resistant silkworm. During his experiments some of the gypsy moths escaped. Gypsy moths spread locally as young larvae ballooning on air currents and artificially as egg masses on objects moved by people. The moth now infests much of the northeastern U.S. The states most severely infested by the gypsy moth include Connecticut, Delaware, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Vermont, Virginia, and West Virginia.

GM hitchhikers to Oregon
egg masses on tire
Egg masses on vehicle tire
How do gypsy moths get to Oregon?
Gypsy moths are notorious hitchhikers. The female moth lays her eggs on any solid surface such as tree trunks, outdoor furniture, recreational and other vehicles, firewood, bird or doghouses, toys, etc. When objects on which eggs have been laid are later moved, gypsy moths are transported with them, sometimes for long distances. Infested items brought from the northeastern U.S. are the main source of gypsy moth infestationsin Oregon.

Asian gypsy moths
How do Asian gypsy moths get to the U.S.?
Gypsy moths occur in North America, Europe, and Asia. The Asian gypsy moth strain has also become established recently in Germany and other European countries where they hybridize with European gypsy moths. Asian gypsy moths have arrived in the U.S. on bulk cargo ships, ship containers, and cargo and outdoor articles from infested areas of Asia and Europe during the 1990's. These introductions in the U.S. have been successfully eradicated.

GM hosts
Gypsy moth caterpillars feed on several hundred species of trees and shrubs. Preferred broad-leaved hosts include oak, apple, alder, aspen, filbert, willow, birch, madrone, cottonwood, and plum. Coniferous species such as Douglas fir, pine, and western hemlock are suitable hosts as well. Tree species not favored by the gypsy moth include ash, balsam, fir, catalpa, cedar, dogwood, sycamore, rhododendron, and tulip tree.

Why is GM a serious pest?
forest defoliated by gypsy moth
Forest in summer after being defoliated by GM caterpillars
Why is the gypsy moth a serious pest?
Gypsy moths have a tremendous capacity to increase in numbers and feed on a wide range of trees and shrubs. Populations can rapidly build to large infestations causing widespread defoliation, weakening or sometimes killing trees. Defoliated forests are susceptible to disease, fire, erosion, and may provide a poor habitat for other forms of plant and animal life. Defoliation reduces the aesthetic, recreational and economic value of forests, parks, and wooded homesites. Newly infested states are subject to restrictive quarantines to prevent further spread of the insect. When numerous, gypsy moth caterpillars can become a nuisance by crawling over such objects as buildings, vehicles, roads, and lawn furniture. Some people suffer allergic reactions when they contact hairs from the caterpillar.

Life cycle
egg mass
Gypsy moth egg mass
Gypsy moth life cycle
The gypsy moth goes through four life stages: egg, larva (caterpillar), pupa, and adult. It has one generation per year and overwinters in the egg stage. Each female lay 50-1,000 eggs in one mass covered by velvety golden or buff-colored hairs from the female's abdomen. The egg mass is about 3/4 inch wide and 1- 1 1/2 inches long and is attached to trees, logs, rocks, buildings, bird houses, and on outdoor household articles.

Gypsy moth caterpillar
gypsy moth caterpillar
gypsy moth caterpillar
Caterpillars hatch from eggs in late March in June. When about half-grown the caterpillar acquires 5 pairs of blue bumps and 6 pairs of red bumps on its back. These blue and red bumps distinguish gypsy moth caterpillars from other kinds of hairy caterpillars. The fully grown caterpillar is about 1 1/2 to 2 inches long.

Gypsy moth pupa
gypsy moth pupa
Gypsy moth pupa
The fully grown caterpillar is about 1 1/2 to 2 inches long. In July the caterpillar transforms into a non-feeding stage called the pupa. The adult moth develops inside the hard, dark-brown pupa. The pupa is attached to solid objects by several strands of silk, often with the last skin shed by the caterpillar attached to its pointed end.

Adult gypsy moth
gypsy moth adults
Adult male and female
Adult moths begin to emerge from pupae in mid-July. The female moth (2 inch wing span) is white with brown zigzag markings on the forewings. The male moth is smaller (1 1/2 wing span) with mottled brown forewings. It can be recognized by two feather-like antennae on its head. Adult moths do not feed. They live for about one week, during which time they mate. Females lay eggs during August and early September starting the life cycle over again.

How you can help
How can you help stop the gypsy moth?
  1. Report suspected gypsy moth life stages to Oregon Department of Agriculture.
  2. Encourage anyone you know who has moved here recently from the northeastern U.S. to contact the Oregon Department of Agriculture for a free inspection of outdoor household articles and recreational vehicles.
  3. Cooperate with Oregon Department of Agriculture seasonal survey staff when they request permission to place traps on your property during the summer.
  4. Observe quarantine regulations by not moving wood products, firewood, plant material, outdoor household articles, or recreational vehicles out of gypsy moth infested areas without certification.
  5. Be especially alert for and report to ODA any suspected egg masses and pupae which can travel to the U.S. on cargo, containers, and conveyances from Europe, Russia, China, and other infested areas.

Additional information
gypsy moth eradication program

other insect surveys

annual report