The insect has one generation per year, over-wintering in the egg. The egg masses are brown to cream colored patches averaging about 1 ½ inches long with a "furry" texture. The egg masses are found in sheltered areas on trees,

buildings, vehicles, outdoor furniture, etc. It is the relocation of these egg masses by humans that has been most responsible for the spread of the gypsy moth.

In April or early May the eggs hatch and the tiny caterpillars move into the tree canopy. There they hang from a silk

thread and are dispersed by the wind. They then begin to feed on the newly emerging leaves. The larvae grow very fast and reach a length of 1 ½ to 2 ½ inches long in about a month. The larger caterpillars have pairs of red and blue dots on their backs and tufts of hair along their entire length.

It is during the caterpillar stage that the pest is destructive. Each caterpillar can eat one square yard of foliage in its lifetime and a major outbreak can easily defoliate an entire woodlot. The preferred host trees are oak, aspen, birch, alder, willow and apple. Less preferred are pine, spruce, beech, cherry, and hemlock. Trees not favored are ash, fir, walnut, maple, cedar, and sycamore.

The caterpillar stage is when the pest is most vulnerable to its natural controls. Parasitic flies, wasps, viruses, bacteria, predator insects, birds and rodents all take their toll. Insecticides are useful at this stage since most insecticides must be ingested by the caterpillar to be effective.

Timing is very important in insecticide treatments. The caterpillar is most susceptible when small and feeding on the newly formed leaves. But all the gypsy moth eggs do not hatch at the same time so there may be a variety of larvae sizes at any one time. Also the trees put out their leaves at different times giving the larvae a variety of foliage to eat. It is important to adjust for these factors when planning insecticide use and to realize that, because of all these factors, no method is 100 percent effective.

In early July the larvae enter the pupa (cocoon) stage where they remain for about two weeks before the insect emerges as the adult moth.

The white adult female does not fly. She attracts a brown male (which does fly), mates and lays her eggs; all very near the place she emerged as an adult. Neither the male or female adult gypsy moth feed and they die within about two weeks of emerging.