If you’ve walked in New England woods recently, chances are great that you’ve noticed light tan moths with a one-inch wing span flitting about — an odd sight for this late in the year. These are male Bruce Spanworm Moths (Operophtera bruceata), also called Winter Moths, as the adults are active from October to December. They belong to the Geometer family of moths, the second largest family of moths in North America, which includes many agricultural and forest pests. The males are seeking wingless, and therefore flightless, females to mate with. Eggs are laid in the fall, hatch in the spring, the larvae pupate in the summer, and emerge as adult moths in the fall. Bruce Spanworm larvae periodically defoliate hardwood trees, preferring the buds and leaves of sugar maple, American beech and trembling aspen trees.
Depending on the woods you walk in these days, you may be greeted by a flurry of inch-long, tan wings belonging to male Bruce Spanworm moths (Operophtera bruceata). From October to December these moths emerge , mate and lay eggs. Females cannot fly; they crawl up the trunk or branch of a tree and send out pheromones to attract winged males. After mating, the female lays eggs which initially are pale green, but become bright orange with age. The eggs hatch in the spring, and the larvae feed on a wide variety of deciduous leaves, favoring trembling aspen, willows, sugar maple and American beech. Periodic outbreaks of these caterpillars can result in heavy defoliation. In 1958 in Alberta, Canada, at the peak of a 10-year infestation, over 50,000 acres were moderately or heavily affected by Bruce Spanworm larvae.