December Winter Moth Flight

Male winter moths landing on a tree trunk. (Photo: D. Swanson/UMass Extension) During the evenings of late fall and early winter, perhaps you’ve noticed clouds of small brown moths fluttering or clustering around porch lights.  Millions of tiny brown moths have been reported from Nantucket to Worcester.  What you have likely seen is the adult stage of a defoliating insect called winter moth.

Although the moth doesn't cause any harm while trees are dormant, heavy winter flight means lots of mating moths, resulting in lots of hungry caterpillars that can eat their way through buds and leaves during the spring.

Throughout Eastern Massachusetts, moths emerge from the soil in mid-November and may continue activity through January.  Male moths are light brown to tan in color, strongly attracted to lights and are often found flying around lamps or holiday lights. Females are gray, nearly wingless and emit a pheromone to attract males.  After mating, the female lays dozens of eggs, the adults die and the eggs over-winter until spring.

A close up view of both winged male and wingless female adult winter moth. (Photo: R. Childs/Umass Extension)

Eggs hatch when temperatures average about 55º F, which in our area is usually between late March and mid-April. This means egg hatch occurs just at or before bud break of most plants. After hatching, caterpillar larvae feed within flower and foliar buds of host plants such as maples, oaks, crabapples and cherries.  Once a bud has been devoured, the caterpillar migrates to another and the process repeats.

Older larvae continue to feed as leaves expand and are capable of defoliating entire trees.  At maturity, the pale green inch long caterpillars drop to the ground, pupate, and emerge from the soil as adult moths in mid-November.

Since first identified in Massachusetts in 2002, winter moth populations have tended to fluctuate in the Greater Boston region.  Winter moth caterpillars can defoliate a wide variety deciduous plants quickly putting maples, oaks, cherries, basswood, ash, elm, crabapple, apple and blueberry plants at risk.  So if you see the swarms of moths now, be prepared for defoliated and damaged trees in the spring.

Feeding injury to a maple caused by the winter moth. Much of this injury occurred while the leaves were still within the bud. (Photo: R. Childs/UMass Extension)

While the potential for defoliation is high, damage can be effectively managed.  Preventative treatments require precise timing, beginning in early spring before leaf and flower buds open.  Barrett Tree Service East chooses to use bio-rational materials, providing effective targeted insect control while minimizing impact to the environment.

If you have seen evidence of winter moth (previous defoliation, green inchworms or moth flight), contact a Certified Arborist at BTSE to discuss strategies for protecting your important trees.

For additional winter moth information visit UMass Extension: (http://extension.umass.edu/landscape/fact-sheets/winter-moth-identification-management).