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Michigan State University Extension
21885 Dunham Road, Suite 12, Clinton Township, MI 48036
(586) 469-6440

Lymantria dispar Suppression




The Macomb County Lymantria dispar (formerly known as Gypsy Moth) Suppression Program was established in 1993 and is administered by Michigan State University (MSU) Extension. The program is provided to residents in both rural and urban areas within the county.

Why is there a Lymantria dispar Suppression Program?

The Lymantria dispar (LD) is a foreign pest with few native predators to keep populations in check here in the United States. It was introduced to Massachusetts in 1869 and has spread across the much of the northeast. LD outbreaks began to occur in the lower peninsula of Michigan in the mid-1980’s. Caterpillars feed on tree leaves, preferring those of oak, aspen, poplar, and birch but will feed on over 500 types plants throughout the summer. Large populations can defoliate entire wooded areas. Caterpillars in large numbers (and their waste, frass) are a nuisance in residential areas. LD's cannot be eradicated, but they can be suppressed to tolerable levels.

What are the goals of this program?

  • Reduce high caterpillar populations to tolerable levels
  • Reduce tree loss by preserving at least 60% tree foliage, to reduce stress on trees
  • Prevent indiscriminate use of chemical controls
  • Provide educational information

How are LD populations suppressed?

The main defense is an aerial application of Bacillus thuringiensis var. kurstaki (Btk), used to reduce high populations of LD caterpillars at sites that meet certain guidelines for treatment. Btk is a naturally occurring bacterium found in the soil and is not harmful to pets, birds, fish, plants, beneficial insects, or humans. Btk specifically targets only caterpillars of a certain age. It is applied when the caterpillars are young (usually in May) to insure the greatest impact in reducing numbers. Alternative mechanical techniques, such as tree banding, egg mass scraping, and hormone traps to help reduce populations. The Suppression Program recommends the use of a combination of methods.

What is the LD life cycle?

The LD life cycle has four main stages: egg, caterpillar, pupae, and moth.

Egg stage

In mid-August, after mating with the male moths, the females lay their eggs in masses. Egg masses are generally firm, oval shaped, about the size of a quarter, and buff or tan colored. Egg masses are laid on any surface, such as tree bark, rocks, woodpiles, decks, buildings, and outdoor equipment. Since lymantria dispar complete only one life cycle per year, eggs laid in mid-August do not hatch until spring.

Lymantria dispar egg mass starting to hatch with many small caterpillars emerging.
Photo credit: USDA Forest Service, USDA Forest Service,


The eggs hatch into caterpillars late April or early May. Hatch date is directly affected by weather. The colder the spring, the later the eggs hatch. A healthy egg mass can hold 1000 eggs, although the average is probably between 300 and 500. Once the eggs hatch, the caterpillars will remain on the egg mass for a few days before they leave to feed. In its short lifetime, a caterpillar can eat one square meter of leaves. Mature caterpillars are about 2” in length with long hairs grouped in bundles. They have 5 pairs of blue dots and 6 pairs of red dots running down their backs. Their heads are black with yellow markings.

Lymantria dispar caterpillar.
Photo credit: Daniel Herms, The Ohio State University,


In mid-July to mid-August, mature caterpillars stop feeding and weave silk around their bodies to form a hard, brown shell or cocoon. In this pupa stage, caterpillars start their metamorphosis or change into the moth stage of the life cycle. This process takes about two weeks.

Three lymantria dispar egg masses on the trunk of a tree with a pupae casing (left).
Photo credit: Daniel Herms, The Ohio State University,


Moths, the adult stage of the life cycle, emerge from the pupal cases in mid-August. The moths do not eat and they live only for a week. Female moths have white wings with brown chevron or ‘V-shaped’ markings and do not fly. Male moths have smaller brown wings and are able to fly. Attracted to a pheromone emitted by the female, the males can fertilize several females before dying. Female moths lay egg masses that remain dormant until spring.

Adult female (right) on an egg mass with an adult male (left).
Photo credit: Daniel Herms, The Ohio State University,

How do LD's travel?

Caterpillars hang in trees on a silk strand and can be carried a great distance by the wind. Humans also move egg masses or pupal cases on travel trailers, firewood, cars, etc. Vehicular travel is how they came to Macomb County! Make sure you do not give the LD a ride.

How do I know if I have LD?      

A number of MSU Extension bulletins can help you identify the LD and caterpillar. You can also use the Macomb County MSU Extension diagnostic facility. There is a small fee for some services.

What does LD damage look like?

Lymantria dispar caterpillars feed on tree leaves creating ‘swiss cheese’ type holes. They do not cause pre-mature leaf drop, browning, or curling of leaves. They do not make a web or tent in trees. In addition to damage to the trees, LD caterpillars can be a nuisance if populations are high enough. Caterpillars and their frass (feces) can drop down from trees on to sidewalks, driveways, yards, porches, and vehicles. The hairs on the caterpillars can cause irritation or an allergic reaction to bare skin. Frass can stain surfaces, especially if it is rained on or becomes wet.

What happens when trees are defoliated?

Trees defoliated more than 40% become stressed by using next year’s energy reserves to grow new leaves during the same season. Healthy trees may withstand several years of defoliation. Evergreens are unable to replace their needles and may die when defoliated. Keep trees watered and fertilized to reduce any stress.

Should I report an LD infestation?

Yes! To determine if your property is eligible for the Lymantria dispar Suppression Program, report all infestations to the program coordinator at the Macomb County MSU Extension office.  An egg mass survey can be done to assess the level of infestation and determine if an area qualifies for the program.  For more information, please contact:

Macomb MSU Extension Lymantria dispar Suppression Program (586) 469-6432.



MSU Extension staff held an informational webinar about the LD Suppression program in February, 2021. The recording can be found here.

The 2022 spray date will be Monday, May 23, 2022. Spraying will occur after sunrise. Please note the timing of the treatment depends upon weather conditions and could be subject to change. Backup date will be Tuesday, May 24, 2022.

Aerial view maps of spray blocks in Macomb County municipalities that have been identified with LD infestation for 2022.

Bruce #1 - Pearl Drive

Bruce #2 - Fisher Rd and Fisher Estates Lane

Bruce #3 - 37 Mile Rd

Bruce #4 - Van Dyke Ebling

Bruce #5 - Rapp Rd

Bruce #6 - Van Dyke

Bruce #7 - Country Manor

Clinton #1 - Moravian and Harrington

Clinton #2 - Dunham and Elizabeth Rds

Lenox #1 - 30 Mile and County Line

Memphis #1 - Main Street

Ray #1 -31 Mile Rd - Gass Farms

Ray #2 - Hall Area

Ray #3 - Timberwood

Richmond Twp #1 - Memphis Cemetery

Washington #1 - Mt. Vernon and Dequindre

Washington #2 - WhispHills (Mt. Vernon and 28 Md)

Washington #3 - Mt. Vernon and 28 Mile Rd


Useful Links and Factsheets

About Lymantria dispar - Trifold Printable Brochure, MSU Extension

Lymantria dispar - Integrated Pest Management, Michigan State University

Lymantria dispar outbreaks in Michigan, MSU Extension

Btk: One management option for Lymantria dispar, MSU Extension

European Gypsy Moth, USDA APHIS

Gypsy Moth, Penn State University Extension