Introduction
Invasive insect introduced from Europe to the United States via Canada.
Most commonly observed:
Late fall to early winter as an adult white moth.
Spring as a tiny green caterpillar.
Emergence
Adult winter moths emerge from the ground in November or December.
Only males can fly, while females climb trees/buildings.
Males are attracted to females by pheromones emitted by females.
Mating and Egg Laying
After mating:
Females lay approximately 150 eggs under tree bark or in crevices.
Lifespan of the female ends after egg-laying.
Hatching
Eggs hatch in March or April into smooth green inchworms with narrow white stripes.
Feeding & Dispersal
Caterpillars use silk strands to balloon into tree canopies.
They cause damage by feeding on tree buds and leaves.
Often drop to nearby shrubs like roses when feeding.
Pupation
After feeding ends in mid-June, caterpillars migrate to the soil to pupate and emerge as moths.
Defoliation
Most visible effect of winter moths:
Significant defoliation of trees and shrubs in spring.
Affected trees in Massachusetts include:
Maple, oak, ash, and various fruit trees (apple, crabapple, blueberry).
Damage Severity
Heavily infested trees may become completely defoliated.
Healthy trees can produce a second set of leaves, but this causes stress.
Research indicates:
Complete defoliation can reduce oak species' growth rates by up to 47%.
Successive defoliations can kill branches or entire trees.
Environmental Factors
Prolonged cool springs allow more feeding time for caterpillars.
Drier years increase tree stress.
Infestations of other pests and diseases can worsen tree health.
Natural Control
Parasitic flies (Cyzenis albicans) are being used to combat winter moth populations:
Flies lay eggs on leaves eaten by caterpillars.
Larvae consume the caterpillar from within, causing death.
Fly pupates inside the dead caterpillar.
Homeowner Actions
Check for inchworm caterpillars in April.
Minimize damage with the following methods:
Supplemental watering to help trees recover.
Use sticky banding traps around tree trunks to catch adults.
Limitations of Control Methods
B.t. (Bacillus thuringiensis kurtstaki) can kill young caterpillars but may also harm native butterflies.
Sticky bands can become ineffective quickly and may not prevent egg-laying.
Additional sprays are recommended for fruit orchards to prevent damage.
Awareness of winter moth life cycle and damage can help mitigate their impact on local ecosystems.