What’s Eating My Trees?

Release Date: Jul 13, 2021

Contact(s): Franklin Pemberton, Lindsey Lewis

Milwaukee, WI (July 13, 2021) – Forest owners throughout the Northeast and Midwest have reported increased defoliation this year due to forest pests, most notably by the Lymantria dispar caterpillar (previously known by the common name gypsy moth). Widespread leaf loss has been noted throughout the region with significant impacts reported in Connecticut, Michigan, New Hampshire, New Jersey, New York and Pennsylvania. This year’s extensive damage could be due to a hot, dry spring as well as the Lymantria dispar’s population cycle, which leads to outbreaks every 10 to 15 years.

The Lymantria dispar is a non-native invasive insect that has been among the most damaging forest pests in the eastern United States in the last 100 years. The caterpillars can be identified by their long hairs and blue and red dots down their back. By some estimates, one Lymantria dispar can eat up to 1 square yard of leaf tissue when it is in caterpillar form for five to six weeks in spring and early summer.

Forest owners and homeowners with defoliated trees this year should be patient. Even when most of its leaves are eaten, a tree is not necessarily dead. In most cases, trees will put out new leaves within a couple of weeks. During a hot, dry summer, watering can help these new leaves grow. While being mindful of local watering restrictions, tree owners are advised to give defoliated trees about an inch of water for each week without rain, either slowly through a hose or with a sprinkler. To reduce possible damage in 2022, tree owners can look for egg masses this fall and remove or destroy them before they hatch next spring.

Lymantria dispar caterpillars feed on more than 300 species of trees and shrubs but prefer oaks. They will also feed on basswoods, birch, poplars, willows and many ornamental trees, such as crabapples. After defoliating their preferred trees, they can switch to less preferred trees like maples, pines and spruce. Defoliation is more damaging to pines and spruce because most evergreens only develop needles in the spring. These needles are usually retained for years instead of being shed in the fall like deciduous leaves.

The USDA Forest Service Eastern Region has been working with states to assess the damage and extent of the Lymantria dispar infestation. Since 2000, the Forest Service has partnered with states through the Slow the Spread program, which focuses on preventing the growth of Lymantria dispar populations in areas where they were previously not found. The Eastern Region also provides funds for suppression treatments in states with outbreaks. This year, the Forest Service Eastern Region Forest Health Protection program has provided more than $7 million to assist with local forest health efforts in states across the Eastern Region, including Lymantria dispar suppression treatments in Pennsylvania, Maryland, and New Jersey. Forest Health Protection will continue to work very closely with its partners to manage native and non-native pests and reduce the flow of invasive forest pests into the U.S.

To learn more about Lymantria dispar, check out Forest Insect and Disease Leaflet 162. This Forest Service publication discusses Lymantria dispar identification, life history, spread and distribution, treatment options and much more. For additional information about the forest conditions in your state and a regional summary, see the Annual Forest Health Condition Reports.  For general tree planting and care information, the Tree Owner’s Manual is one of the most popular Forest Service publications.


Lymantria dispar
Lymantria dispar
Lymantria dispar
Lymantria dispar