Winter Moths

Adult winter moths emerge from the ground in November or December, but only the male is able to fly. The female climbs to the base of a tree or building and attracts the male.

After mating the female lays a cluster of approximately 150 eggs under tree bark or in tree crevices.  Then the female will die off.
In March or April the eggs hatch into a smooth green inchworm with a narrow white-stripe running lengthwise on each side of the body. The caterpillar spins a strand of silk, which, with the help of air currents, takes it into tree canopies in a dispersal method known as “ballooning.”
Once there, the damage to the tree begins as the caterpillars work their way into the tree buds and leaves to feed. Winter moth caterpillars can also drop from trees to nearby ornamental shrubs such as roses. When feeding ends in mid-June the caterpillars migrate into the soil to pupate and emerge as moths.
The most visible effect of the winter moth infestation is the destruction of trees and shrubs in spring. In Massachusetts, winter moths affect maple, oak, and ash as well as fruit producers such as apple, crabapple, and blueberry. Newly-hatched caterpillars burrow into the buds of trees and shrubs before they open, and begin to feed; when they finish with one bud they move to another.
The most heavily infested trees may be completely defoliated, and while healthy trees are capable of putting out a second set of leaves, the process puts severe stress on the tree. Research has shown that complete defoliation can reduce the annual growth rate of some oak species by as much as 47%, and successive defoliations can kill branches or entire trees.
The impact of the caterpillars may also be exacerbated by secondary effects such as prolonged, cool springs, which allow the caterpillars to feed longer in the buds; dry years which put trees under additional stress; and infestations of other insects such as bark beetles, fungal parasites, or other moth species.

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