Return of the Winter Moth

Heavy fog rolled into Boston on the evening of Thursday, December 5. A thick blanket of darkness lay over Jamaica Pond.

Jamaica Pond in fog
Jamaica Pond in fog

Unusual warmth accompanied the fog, and winter moths (Operophtera brumata) were out in force. I saw one on a shrub covered in Christmas lights.

Winter moth on a shrub with Christmas lights
Winter moth resting on a shrub

It was the second day this year I had noticed these moths. The first, November 27, was also unusually warm (62°F/17°C) after a low temperature the previous day of 32°F/0°C, bringing with it heavy rain. December 5 followed that pattern, warm (57°F/14°C) after a low the previous day of 35°F/2°C, with some rain.

Winter moths are native to Europe. Lacking natural predators, their numbers have exploded in Massachusetts, to an estimated one trillion in 2011. They are one of the few insects that can be seen in winter, even after a few days of sharp freezes.

Winter moth
Male winter moth

The moths in flight are all males, looking for mates. Female winter moths have tiny, vestigial wings. They climb trees or other objects and release pheremones, which the males use to find them.

Female winter moth on a fence
Female winter moth on a fence in Cambridge

Joe Elkinton, a professor at UMass-Amherst, has brought a parasitic fly to the state to help control the winter moth population. The fly, Cyzenis albicans, preys only on winter moths and has been effective in Nova Scotia and British Columbia. The fly now has an established population in Massachusetts. If all goes according to plan, we will see only a small population of both the fly and the moth in the future.

Male winter moth
Male winter moth

More information on winter moths: UMass Extension.

This entry was posted in Nature and tagged , , , , , , , , . Bookmark the permalink.

Comments are closed.