Introduced Species Summary Project
European Gypsy Moth (Lymantria dispar)

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Common Name: Gypsy Moth, European Gypsy Moth

Scientific Name: Lymantria dispar


Phylum or Division: Arthropoda
Class: Insecta
Order: Lepidoptera
Family: Lymantridae
Subfamily Lymantrinae

Identification: The gypsy moth goes through complete metamorphosis.  It is only during the larval stage that gypsy moths are able to eat.

Egg masses: about 1.5 inches long and .75 inches wide, oval shaped, covered with hairs from the female’s abdomen.  The buff-colored egg masses contain between 100 to 1,500 eggs.  They can be found on the undersides of tree limbs, bark, rocks, and man-made objects such as buildings, campers, outdoor furniture, garbage cans, and swing sets.  The eggs over winter and hatch the following spring, usually mid to late April and through May in some areas. 


Larva (caterpillar) - male caterpillars go through five instars before entering the pupal stage; the females go through six.  Newly hatched caterpillars are brown to black; covered with hair; about 1/8 inch long. Mature caterpillars are gray to black; up to 3 inches long; have a yellow stripe and two rows of red and blue dots along the back; long hairs cover the body.  Caterpillars are usually done feeding and ready to enter the pupal stage during late June-July.


Pupa - dark reddish brown, usually with some yellow hairs attached; females are larger than males - 15-35mm and 15-20mm respectively.  This stage begins about 8 weeks after eggs hatch, and lasts about two weeks.  The males usually emerge one or two days before the females.  They can be found in protected areas such as bark fissures or crevices, underneath loose moss, and in leaf litter.   


Adult - Females are whitish in color with darker wavy bands across the forewings; wingspan ranges from 37-62mm; flightless.  Males are tan to brown with irregular black wing markings; plumose antennae; wingspan ranges from 37 - 50mm.  Males will then use their plumose antennae to detect pheromones emitted by the flightless females.  After mating, the eggs are usually laid from July through September.


 Original Distribution: Mainly temperate regions; Central and Southern Europe, North Africa.  An asian race can be found in southern Asia and Japan.


Current Distribution: Northeastern United States - Vermont, Massachusetts, New Hampshire, Rhode Island, Connecticut, New York, Pennsylvania, New Jersey, Delaware, Maryland, Wisconsin, Michigan, Illinois, Indiana, Ohio, West Virginia, North Carolina, Virginia, Maine

Northwestern United States - California, Utah, Oregon, Washington

Canadian Provinces of Ontario, Quebec, and British Columbia

Site and Date of Introduction: Lymantria dispar was brought to Medford, Massachusetts in 1868.

Mode(s) of Introduction: Etienne Leopold Trouvelot, a French astronomer with an interest in insects, was hoping to begin a commercial silk industry and had the idea of breeding L. dispar with local silkworms to develop a strain that was resistant to disease.  Some of the caterpillars escaped from Trouvelot’s backyard and moth populations became established in local areas.  The first outbreak of L. dispar began in the Boston area just ten years after the escape.  Efforts to eradicate gypsy moths during this time have failed and the species continued to spread, and still continues to spread, throughout the Northeast.


Short distance dispersal of this species is done through ballooning.  This is where the caterpillars are wind blown and dispersed.  The spread of gypsy moths to the Northwest is thought to be by the transport of egg-laden materials by humans.  Females lay their egg masses on man-made objects such as vehicles.  Gypsy moths became a concern in the Northwest between 1970 and 1980.


Reason(s) Why it has Become Established: Although the Gypsy moth has been in the United States for nearly 135 years, and has spread throughout the Northeast, the spread has been relatively slow.  This could be due to the fact that females cannot fly so it may take longer for the species to reach surrounding areas and flourish.  This does not exempt the Gypsy moth from being a successful colonizer of the Northeast.  This success is partly due to the fact that female gypsy moth egg masses may contain over 1,000 eggs and the caterpillars that hatch from those eggs are capable of feeding on over 300 species of trees and shrubs; some sources escalate this number to 500 species. Host plants include but are not limited to oak, basswood, willow, birch, hemlock, pine, chestnut, sweetgum, and poplars.  This generalistic feeding behavior allows the caterpillar to persist in a variety of areas.

Because the gypsy moth is not native to the United States predators, parasitoids, and diseases that would feed on the egg masses in its native habitat are not present.  

Ecological Role: Gypsy moth caterpillars are major defoliators of deciduous forests.  Although they have a variety of hosts, oaks are preferred.  There are some birds that feed on Gypsy moths but their main predators are small mammals.  Populations of Gypsy moths oscillate with periodic eruptions.  Low-density populations grow exponentially into an outbreak phase. Significant damage to trees takes place during these outbreaks.  Small mammal predators are what is thought to maintain low-density populations.  A 10-year study was done on the relationship between white-footed mice, oaks, and gypsy moths in Massachusetts.  The study found that increases in density of gypsy moths were associated with declines in density of the white- footed mouse, a predator, and changes in density of the white-footed mouse were closely associated with mast crops of acorns.

Benefit(s): The only potential benefit the Gypsy moth could have on an area is if it’s host plant is a problematic introduced species.  Because of the Gypsy moth’s generalistic feeding behavior, this species is unlikely to khave any profound positive effects in any area it has been established.

Threat(s): Gypsy moth caterpillars have been known to defoliate 13 million acres of trees in the United States in one season.  They are a serious threat to urban shade trees and ornamentals.  Young trees can tolerate a single defoliation but defoliation of an older tree will make them more susceptible to other stresses such as drought and disease.  Once a tree is defoliated it will use up much of its energy to produce new leaves, this could have an effect on its growth.  Repeated infestations will continue to weaken the tree, even a young tree, eventually killing it. Overtime we will begin to see changes in the landscape and this could have an effect on organisms that rely on the plants for food, shelter, and shade.  Losing oaks, an ecologically dominant species, is also of concern.  Losing trees also has impacts on timber production, tourism, and recreation.

Control Level Diagnosis: “Highest Priority” - According to the USDA Forest Service, State and Private Forestry, the spread of the gypsy moth is happening at a faster rate than in the past and could infest much of the South and Midwest during the next 30 years.  Therefore, it is crucial that this species continues to be monitored and controlled in these areas.

Control Method: Millions of Federal and State tax dollars have been spent on Gypsy moth control.  The approaches that have been taken to control Gypsy moths in the United States include suppression, eradication and slowing the spread.  Suppression and eradication efforts include the use of chemical pesticides such as Bacillus thuringiensis and diflubensuron (Dimilin);biological pesticides introduced to Gypsy moth infested areas over the last 100 years such as Entomophaga maimaiga which is a fungus that caterpillars will come in contact with when they are crawling on the ground; and pheromone traps to trap males. Trapping is also used to monitor reproducing populations. 


Slowing the spread efforts include the United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), Plant Protection Quarantine (PPQ) program.  PPQ’s Gypsy moth program is a Federal-State partnership that regulates the control of the artificial transport of the Gypsy moth to areas that are not already infested.  This program makes it mandatory for anyone who is moving from a regulated area to thoroughly inspect any outdoor items they will be transporting.  Regulated areas include areas of Wisconsin, Michigan, Illinois, Indiana, Ohio, West Virginia, North Carolina, Virginia, and Maine and all of Maryland, Delaware, New Jersey, Pennsylvania, New York, Connecticut, Rhode Island, Massachusetts, Vermont, and New Hampshire.  However, this is rarely enforced.


The National Gypsy Moth Slow the Spread Program (STS) is a program that became a National implementation in 1999 after a successful pilot program that was started in 1992.  STS monitors recently established, low-level populations of Gypsy moths found in transition areas. Transition areas are areas between infested and non-infested areas.  Intensive monitoring of these areas will allow for the use of Integrated Pest Management (IPM) strategies to eradicate these populations and slow the spread into non-infested areas. 




Canada Forest Service Center, Forest Pest Leaflet


Gypsy Moth News. January 1998, Issue Number 44


Gypsy Moth in North America


Gypsy Moth in Virginia


J.S. Elkinton, W.M. Healy, J.P. Buonaccorsi, G. Boettner, H.R. Smith, and A.M. Liebhold. 1998. Gypsy Moths, Mice and Acorns. Proceedings:  Population Dynamics, Impacts, and Integrated Management of Forest Defoliating Insects.  USDA Forest Service General Technical Report NE-247.


United States Department of Agriculture – Invasive Species and Pest Management


United States Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection & Quarantine fact sheet.  March 1999.  Don’t Move Gypsy Moth.




Author: Tracy Baczynski
Last Edited: 7 March 2002

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Project Editor: James A. Danoff-Burg, Columbia University