The Gypsy Moth – A Continuing Problem

Gypsy moth larva,USDA Forest Service

Like many other pest introduced for the benefit of this or that, the gypsy moth is an example of an experiment gone horribly wrong. The moth was brought to the United States in 1869 in a failed attempt to start a silkworm industry. Escaping soon after, the gypsy moth has become, over the past century, a major pest in the northeastern United States and southeastern Canada.

Tree damage is caused by the insect larvae, or caterpillars, which emerge from their eggs beginning in early spring and continuing through mid-May. The larvae move to the leaves of trees and begin to eat, mostly at night. During daylight hours, larvae generally seek shade from the sun but feeding can occur in daytime in heavy infestations. Gypsy moth larvae grow by molting, five molts for males and six for females. Feeding occurs in the “instar” stage or period between each molt. As might be expected, a caterpillar’s appetite increases with each molt. Feeding continues until mid-June or early July when the caterpillar enters the pupae stage emerging, finally, as a moth. Both male and female moths exist only to reproduce once with the male moths flying to find the females who are too heavy to fly. After the females lay their eggs from July to September, depending on location, moths of both sexes then die.

The gypsy moth caterpillar is not a fussy eater. It has a preference for the leaves of deciduous hardwood trees such as maple, elm, and particularly oak. Gypsy moths can also feed on apple, alder, birch, poplar and willow trees. As it grows it will also attack evergreens like pines and spruces. Gypsy moths appear to dislike ashes, sycamores, butternuts, black walnuts, dogwoods and balsams. However, during heavy infestations, competition for food will drive the caterpillar to attack almost any tree or shrub.

Depending on the degree of infestation, tree damage ranges from light to almost complete defoliation. Most deciduous trees can survive a moderate degree of defoliation. Many can even survive a single complete defoliation by the gypsy moth caterpillar. However, continuing attacks can fatally weaken a tree or leave it vulnerable to other insects or disease.

Egg masses appear as 1.5 inch (4 cm) tan or buff-colored hairs on tree trunks, outdoor furniture or the sides of buildings.

Gypsy moth caterpillars change appearance as they grow. Young caterpillars are black or brown and about ¼ inch (.6 cm) in length. As they grow, bumps develop along their backs along with coarse, black hairs. Each of the 11 sections of a developed caterpillar will have two colored spots, the first five pairs, blue, and the last six, red. Mature caterpillars can be as long as 2 ½ inches (6.35 cm).

Gypsy moths are seen only in mid-summer. Males are grayish brown and can fly; females are larger, whitish with black marks and cannot fly.

The gypsy moth can be combated at the egg, larval (caterpillar) and adult moth stages.

The Gypsy Moth continues to pose a major threat to our forest in spite of on going aggressive control measures being implemented.

For more information and to find out what you can do to help, visit “Slow the Spread of the Gypsy Moth Foundation.”