The Spongy Moth life cycle has four main stages, and takes one year to complete:
The first part of August, female moths deposit their eggs forming buff or tan colored “masses” that are oval shaped, firm, and about the size of a quarter. These egg masses contain between 50 and 1,500 eggs. Egg masses are laid on any surface, such as rocks, woodpiles, decks, buildings, outdoor equipment and, of course, tree bark. (It is helpful to keep yards clean and free of debris where adult moths could lay their eggs.) Spongy Moth complete only one life cycle per year, and eggs deposited in August do not hatch until spring.
Eggs hatch into caterpillars in late April or early May. Hatch date is directly effected by weather. The colder the spring, the later the hatch. Once they hatch, the caterpillars will sit on the egg mass a few days before leaving to feed. In its short lifetime, a caterpillar can eat one square meter of leaves. The warmer the temperature, the more the caterpillars feed and develop, generally feeding at night and resting during the day. Mature caterpillars are about 2” in length with long hairs grouped in bundles. They have a head with black and yellow markings, and five pairs of blue dots and six pairs of red dots running down their backs.
In mid July to mid August, mature caterpillars stop feeding and weave silk around their bodies to form a hard, brown shell or cocoon. This is the pupa stage, when caterpillars start their metamorphosis or change into the moth stage of the life cycle. This process takes about two weeks.
From pupa cases, moths or the adults emerge. Moths do not eat, and live about a week. Female moths have white wings with brown chevron or “V-shaped” markings, do not fly, but emit a pheromone to attract the males. The males have smaller chevron marked brown wings, are able to fly, and fertilize several females before dying. Females deposit egg masses encased in hairs from their abdomen. Eggs are dormant until spring (late April or early May).