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Dorsal view of three Gypsy Moth caterpillars. Grey with blue and red spots on the left. White with red spots in the middle. Grey with dark black stripe and red spots on the right. All very hairy!
Multiple Gypsy Moth caterpillars on several plant leaves each containing holes where the caterpillars have been feeding.
Dorsal view of a white female Gypsy Moth on top (top) and smaller, dark brown male Gypsy moth (bottom).
Closeup of a Gypsy Moth
Moody side view of an adult female Gypsy Moth.

European Gypsy Moth

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What is it

The Gypsy Moth is a native of Eurasia that was introduced to North America, specifically Boston, Massachusetts, in 1869 as an attempt to start a silkworm industry. Some of the moths escaped and have become a major pest in the northeastern United States and southeastern Canada. However, every state has the potential for an infestation since they all contain habitat that is considered suitable for Gypsy Moths.

Damage to trees is caused by the caterpillars that emerge in the spring and feast on the trees’ leaves. The caterpillar feasts on leaves until late summer when it pupates to turn into a moth. They have the potential to completely defoliate a tree. The caterpillars prefer deciduous hardwoods, especially oak, but in heavy infestations, the caterpillar will dine on any kind of tree, including evergreens.

The mature caterpillars are between 50-65 mm long and identifiable by their yellow and black heads and a distinctive body pattern, 5 blue spots followed by 6 red spots. However, these features are not present in young caterpillar (those measuring less than 12 mm).

As an adult, the moths are sexually dimorphic, meaning they vary in appearance between males and females. Females are larger than males and cannot fly due to their weight. The females are light cream color while the males are a darker brown. Both adults have markings on their wings in the form of dots and scallops. Adult moths do not harm the trees, but lay hundreds to thousands of eggs that develop into damaging caterpillars.

How does it cause harm?

A female Gypsy Moth lays one large mass of eggs (up to 1000 eggs) on the trunk or branches of a hardwood tree during the fall. The egg mass looks like a brown blob on the tree. The eggs remain on the tree over winter and hatch in the spring. When they hatch, the caterpillars disperse by ballooning and spinning silk to carry them. When they land, they start to eat the leaves of the host tree, mostly at night. The caterpillar must molt between 5 and 6 times to become an adult moth and with each molting, the caterpillars’ appetite increases. The caterpillars feed until the end of the summer, turn into moths, then mate, lay eggs, and die.

Gypsy Moth caterpillar can defoliate an entire tree, fatally weakening the tree or leaving it vulnerable to other insects and diseases. Some trees can withstand some defoliating, even a total defoliation, but if the situation continues year after year, the tree cannot take the stress and will die. Gypsy Moths are considered a major threat to commercial forests.

How do we stop it?

Federal agencies have already begun taking actions to try to control the Gypsy Moth population in states and counties where it has been found. Methods to do so include using female pheromone traps to destroy the male moths and spraying areas with a larval pathogen to stop the caterpillar before they do any more damage.

Such methods will take time, but there are things you can do to help control the Gypsy Moth population. One way to prevent the caterpillar from destroying the trees is to destroy egg masses when found. You can also help control the gypsy moth population by trapping and destroying male moths and caterpillers, or by encouraging natural predators, like birds, to visit your trees. To prevent the spread of Gypsy Moth be sure to be aware of quarantine areas (see maps below) and make sure you aren’t bringing Gypsy Moths home. For a full list of tips on how to prevent the spread of such species to your home, check out hungrypests.com.