How Do I Recognize the Gypsy Moth?

Many people confuse the gypsy moth with other common caterpillars that occur during the spring to early summer. As a result, inappropriate or unnecessary controls can be applied. This publication describes the appearance of gypsy moth egg masses, caterpillars, pupae, and adult moths so that the appropriate actions will be taken to manage this important pest of trees and shrubs.

Egg Masses

Gypsy moth eggs are laid in clusters called egg masses. Each egg mass contains from 100 to 1,000 eggs distributed throughout a felt-like mat of hair. This hair is placed on the eggs by the female moth when the eggs are laid. Egg masses are usually 3/4 to 1 1/2 inches in length, are buff-colored (like a camel hair coat), and often attached to tree trunks. However, tree branches, stacked firewood, rocks, houses, lawn furniture, and dog houses are also suitable locations. Egg masses are laid by female moths in mid to late summer (late June through September depending where you live) and remain in the egg stage until the following spring.

Caterpillars

Gypsy moth caterpillars (also known as larvae) emerge from eggs during late spring (April to May) and go through a series of growth stages called instars. Young caterpillars that have just emerged from eggs are about 1/4 inch long and are dark brown to black in color. Once they emerge they spin silk and drop from branches and leaves to disperse when the wind blows. After landing on another tree or branch they quickly settle and begin feeding and growing. At maturity gypsy moth caterpillars grow to nearly 2 1/2 inches. These older caterpillars are dark brown to black in color and covered with long, stiff, black hairs. Each section of the caterpillar bears a pair of colored spots. The first five pairs are blue and the last six are red.

The eastern tent caterpillar, fall webworm, and the mourning cloak are three different caterpillars that can be confused with the gypsy moth. The eastern tent caterpillar appears early in the spring, usually before the gypsy moth. Tent caterpillars live in a large, silken tents in the crotches of trees. Fall webworms appear during the mid to late summer, much later than the gypsy moth, and also live in a protective webbing located at the ends of tree branches. Caterpillars of the mourning cloak butterfly live in large groups, and for this reason, they might be confused with the gypsy moth. However, gypsy moth caterpillars are very hairy, have red and blue spots, are much larger, and therefore easily distinguished from mourning cloak caterpillars.

Pupae

Gypsy moth caterpillars (and moths in general) prepare to become adult moths by changing into a stationary stage called a pupa. Gypsy moth pupae are brown and somewhat teardrop-shaped. Unlike many other moths, gypsy moth pupae are not enclosed in a silken cocoon. Gypsy moth pupae can be found in any protected location.

Adult Moths

Male and female gypsy moths appear in mid-summer and are easily distinguished from one another. The males are brownish-gray in color, whereas the females are slightly larger in size, white in color, and have a few, scattered, black markings. Unlike the males, the females cannot fly.

Most people do not notice adult gypsy moths, but instead notice the caterpillars, the damage they do, and the feces that can seemingly rain down from trees during heavy infestations. However, male moths can also be a nuisance by flying around people's faces.