We'll begin the life cycle of the gypsy moth with the egg stage. Eggs are laid by the adult moths typically in late July. These egg masses which are tan in color, and somewhat hairy, are the overwintering stage of this insect. The eggs hatch in spring, exact time depends on the weather; but typically this happens in late April, early May. When the caterpillars hatch, they are only about 1/8" in length. They begin to feed and grow until they reach a length of about one inch. As they move, they produce a strand of "silk" that enables them to move from one tree to the next by wind. They feed from the time they hatch until they pupate in late June, early July. The young larvae feed during the day, but as they become older, they feed at night and rest during the day.

The caterpillars look for a protective location to pupate. This is typically in the crevices of tree bark, on sides of buildings, or fallen logs. They are in this phase for about 10-14 days. They emerge as adult moths, ready to mate and lay eggs for the next generation. The female moths are unable to fly, so she lays her eggs close to where she hatched from the pupa stage. The female are a mottled brown, while the males are a creamy white. The adults live for about one week.

Thus begins the cycle again with the egg masses on the sides of trees, overwintering until the spring.

So why do we care about the life cycle? The larvae stage is the destructive time of this insect. When populations are high, they can defoliate trees rather quickly. Not only does the defoliation look bad, it also weakens the tree. Their frass, or droppings, can litter walkways, decks and other outside surfaces to the point of not being able to use the outdoor space. The best time to control these destructive insects is early in the larvae stage: early May. The longer you wait, the more difficult to control. Bacillus thuringiensis, or BT, is most commonly used for control. This is a naturally occurring, soil dwelling bacterium. When ingested by the caterpillar, the bacterium produces a toxin that eats a hole in the gut of the larvae. This particular bacterium affects the gypsy moth caterpillar only.

For more information, go to http://ohioline.osu.edu/hyg-fact/2000/2174.html

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