What is Winter Moth?

The Winter Moth (Operophtera brumata) is an exotic invasive insect pest with no natural predators.  The moths appear around Thanksgiving and remain active as long as the temperature is mild.  The green caterpillars emerge in Spring and feed on virtually any tree or shrub.

All deciduous trees are at risk. Research shows that 4 consecutive years of defoliation can lead to tree mortality.

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Where is it from?

Initially, the hardest hit areas were in Eastern Massachusetts, especially southeastern MA, including Cape Cod.  Winter moth was initially introduced to North America from Europe in Nova Scotia sometime prior to 1950.

Susceptible Plants

Oaks, maples, cherries, basswood, ash, white elm, crabapples, apple, blueberry, and certain spruces such as Sitka spruce.

Young larvae (caterpillars) wriggle into buds of apple, blueberry, cherry, crabapple, maples, oaks etc., in the early spring just before or at bud break. Once inside the buds, the tiny caterpillars begin feeding. Delayed bud opening due to cool weather can lead to bud death. Larvae move from bud to bud as they feed. As the larvae grow, they feed in expanding leaf clusters and are capable of creating defoliation in high populations.

Life Cycle of Winter Moth

Each moth lays 100 -200 eggs and the average infested tree has up to 150,000 leaf defoliating caterpillars.

Moths, the adult stage of Winter Moth, emerge from the soil usually in late November and may be active into January whenever the air temperatures are mild. The male moths are light brown to tan in color and all four wings are fringed with small elongate scales. The male moths are strongly attracted to lights and can often be found flying around outside lamps or in car headlights.

The female is gray, almost wingless (brachypterous) and, therefore, cannot fly. She emits a sex pheromone that often attracts clouds of male moths. Females are usually found at the base of trees or scurrying up tree trunks, but can be found almost anywhere. After mating, the female deposits a loose egg cluster in bark crevices, under bark scales, under lichen, or elsewhere. The adult moth’s then die and the eggs over-winter.

Egg hatch occurs in the spring just at or right before bud break of most of the host plants. Some of the newly hatched larvae crawl up tree trunks and produce a silken strand of silk, which makes them air buoyant. This “ballooning” along with wind patterns means that winter moth caterpillars can arrive in areas where they have not been expected.