Eggs: The overwintering stage

Eggs are laid in August and the embryo immediately starts developing during the warm days of summer. In a month, the tiny larva is fully formed and ready to hatch. At this point, however, the larva goes into diapause, shutting down metabolic activities and becoming insensitive to cold. In suspended animation, the larva passes the winter within the egg. As temperatures increase in early spring, the larva inside the egg slowly becomes more active. In mid-May, just as the leaves of trees are expanding, the larva chews through the egg shell and hatches.

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The larva: A feeding machine

Before starting to feed, larvae, or caterpillars as they are commonly known, disperse throughout the forest in a behavior called ballooning. The larva climbs to the top of the tree on which it hatched, and dangles in the air on a silk thread. When a breeze catches the larva, the thread breaks and it is carried on the wind. Fluffy hairs and the silk thread slow the descent of the larva. Most larvae land within 150 yards of where they took off. A very small percentage of the population can be blown long distances, helping the gypsy moth colonize new areas.

Once the larva has finished ballooning, it settles down to feed. It will eat for five to six weeks depending on its sex. Females feed for an extra week to put on the fat necessary to produce eggs. About once a week the larva will grow too large for its exoskeleton and it will molt. These molts separate the larval period into five or six stages, called instars. Early in larval development, instars one through three, larvae feed during the day. Once they reach the fourth instar, however, they start to feed at night and hide under rough bark or in leaf litter during the day, possibly to avoid being eaten by birds. About 90% of the leaves consumed by a larva will be eaten in the last two instars. This is the reason it sometimes seems like trees are defoliated overnight!

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The pupa: The metamorphic stage

When the larva is fully grown (about 1-1/2 inches for males and 2-1/2 inchesfor females), it starts wandering around, looking for a safe place to pupate. They look for a cranny where they will be safe from enemies like mice, birds, and parasitic wasps. Typical hiding places include between ridges of bark, under flaps of loose bark, or in cracks of rock outcroppings. They can also be found in crevices on the undersides of vehicles, in firewood piles, or on outdoor furniture.

Once the larva has found a safe spot, it sheds its skin and its new skin hardens into a dark brown shell. The gypsy moth is immobile for most of the pupal stage while its entire body is rearranged within the pupal shell. After a week or two, the worm-like caterpillar has been transformed into the winged adult moth which then breaks free of the pupal shell.

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The adult moth: They live to reproduce

The gypsy moth adult male and female moths look very different from each other. Females are 1 1/2 inches long and are white with a black chevron on their forewings. Female moths can't fly and will fall to the ground if picked up. Male gypsy moths are mottled brown and gray and have large feathery antennae. They are similar in appearance to many native moths. They can be distinguished, however, by their behavior, as they fly in search of females in the late afternoon not at night.

The only function of the adult stage of the gypsy moth is to reproduce. Unlike many other moths and butterflies, the adult gypsy moth cannot feed. They have about 2 weeks to find a mate before they die. Once the male has found the female, they mate and the female lays all her eggs in a single teardrop-shaped mass and covers it with buff colored hairs from her own body. A female that ate well as a larva can produce 600-1000 eggs in a mass about an inch and a half long. A female that starved in the last 2 weeks of larval development may only produce 50 eggs.

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