Complete life cycle runs April through July 30 *
Eggs mass: Eggs hatch in early spring about the time of bud break, mid-April to mid-May. The caterpillars have five growth stages before pupating, each lasting seven to ten days. Adult moths emerge and lay eggs in late June into early July.
Caterpillars: During the early growth stages, caterpillars remain in clusters on the leaves. As the caterpillars get larger, they consume increasing amounts of leaves and wander widely in search of more food. They often drop from defoliated twigs to the ground. Caterpillars may grow up to 2½ inches long. They do not build tents, but clusters of numerous caterpillars commonly rest on pads of silk on tree stems.
Cocoon: Mature caterpillars spin whitish silk cocoons attached to vegetation, buildings, and other stationary objects to begin pupation. This can occur from early to late June. The pupae form inside the cocoons. Seven to ten days later, adult moths emerge.
Adult moths: Moths are pale tan and have a broad, brown stripe across the front wings. FTC moths are night fliers and are attracted to lights in large numbers. As a result, it is common to find high populations of FTC near populated areas and along highways where lights are often concentrated.
Egg masses overwinter on twigs of host trees: After mating, the female moth lays eggs in ½-inch long clusters wrapped around a twig. Each female lays several clusters of 150 to 200 eggs by early July. A tough, bronze-colored casing covers the egg mass and protects the eggs from drying out until they hatch the next spring. The eggs are resistant to cold and easily survive Minnesota winters. It has been shown that less than 10 percent of the eggs are killed when temperatures reach –40 °F and only 50 percent succumb at –50 °F.
* The timing of biological events varies from year to year because it depending on weather and location. For example, events will occur near the earlier date when spring is early, when May and June are warmer and drier than average, or when the location is south of Mille Lacs Lake.