Alien Profile: Gypsy Moth
Alias (scientific name in latin): Lymantria dispar
Home Land (origination): Europe, Asia and North Africa. In its native range, gypsy moths can be found from the frigid Russian Steppes to the subtropical shores of the Mediterranean where natural enemies such as parasites and diseases keep it in balance with its environment.
Arrival Date: The gypsy moth was brought to North America by Professor L. Trouvelot when he tried to breed a hardy silkworm. Between 1868 and 1869 some gypsy moths escaped when a specimen jar fell from Trouvelot's open window. Later, more moths and caterpillars escaped from small populations growing on shrubs in Trouvelot's garden when high winds blew off protective netting. The professor notified townspeople about the accidents, but nobody thought the gypsy moth was a pest and no one captured or destroyed the escaped insects. The insects soon multiplied in a vacant lot next to Trouvelot's home in Medford Massachusetts.
The insects gradually increased their numbers and spread across the United States. Click here to see how fast they spread. They arrived in eastern counties of Wisconsin by the 1990s.
How to Identify: Look for the gypsy moth in its many forms (stages of life). Check out the Changing Faces of the Gypsy Moth to help identify it in your backyard.
Evidence They are Here: When Gypsy moths have an "outbreak," the caterpillars defoliate trees (eat all the leaves). This typically occurs in mid-June. All leaves on an oak tree can be eaten within a week! Look for leaf damage that looks like the picture shown here. Click here to find out what hungry gypsy moth caterpillars' favorite foods are and what they won't eat.
Note: Most trees can grow a replacement set of leaves ("refoliate") by late July, and the forest will be green again. This is very stressful for a tree and can kill the buds, twigs and/or branches. After that, tree growth slows down for several years and the tree can be attacked by other forest insects and diseases. Trees weakened by defoliation will also stop making nuts, sometimes for years, and wildlife lose out on a food source that they depend on. While the trees are bare, predators can easily find nests and songbirds may lose their young. Lack of shade from the tree makes water temperatures warmer, which lowers the amount of oxygen in the water for aquatic plants and animals. A dense canopy of leaves also buffers the violence of summer storms. When that protection is lost, rainwater erodes the soil and lowers water quality in streams. Fish and other aquatic animals can be stressed during this period before trees "releaf." These are all signs that the gypsy moth has struck an area.
Invaded Territory: Gypsy moths spread quickly across the U.S. because the climate was more suitable here and natural enemies were few. The Medford area experienced a gypsy moth outbreak in 1889, 20 years after the gypsy moths were released. Caterpillars defoliated fruit and shade trees in a 360 square mile area around the city. Local people said they were overrun "by big, hairy caterpillars, so numerous that people slipped on masses of them clustered on the ground, streets and sidewalks" and as "they gobbled away in the trees, their droppings (called frass), like a shower of coffee grounds, drizzled to the ground below." Yuck.
Click here to follow the gypsy moth's invasion and spread across the United States.
Today, gypsy moths can be found across the eastern United States and here at home. They can be found in eastern Wisconsin counties bordered by Lake Michigan from Kenosha through Door County, up to Oconto and Marinette counties. The gypsy moth has moved west very quickly in places where oaks are more abundant like between Milwaukee and Madison and in Waushara, Waupaca, and Portage counties. Many of these eastern counties in our state are under "Quarantine." That means people and business must carefully check things kept outdoors that they want to move. These are things like: plants, wood, furniture, and vehicles. Businesses must check Christmas trees, timber and pulp wood before shipping them on trucks.
Suppression Techniques:Although the gypsy moth will continue to spread, our trees and forests will survive. Gypsy moth outbreaks can be delayed or reduced so that trees and people are less stressed. The most common suppression treatment is a spray of Bacillus thuringiensis, commonly called Bt. This bacterial insecticide kills caterpillars that eat it within a week of spraying. Bt is found naturally in soil and degrades within a week as the sun hits it. Bt does not harm people, animals, birds or fish. Sprays also don't affect gypsy moth caterpillars outside the treated area. Sometimes spray programs are repeated for one to three years when the gypsy moth population is in the outbreak stage. Once the gypsy moth caterpillar population has collapsed in an area, spraying can stop for several years.
Help Stop the Alien Invasion! The rapid migration west of the gypsy moth in the United States is caused by people unknowingly moving egg masses that are attached to cars, firewood, nursery plants and outdoor furniture. One infestation in Virginia began when an unsuspecting person brought home several dog houses from New Jersey that had gypsy moth egg masses on them! Wind can move male moths and young caterpillars, but it doesn't spread the moths rapidly. There are regulations requiring the inspection of logs, nursery plants, Christmas trees and outdoor household items which help reduce the number of accidental introductions, but it won't stop them all. We must teach people about these invaders and have them check the trees in their community.
Here's what you can do: