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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