UMass Extension Winter Moth Update
Editor’ s Note: This is an excerpt from a recent UMass Extension Update. To read the full report, scan the QR code or use this link https:// www. umass. edu / agriculture-food-environment / landscape / news / noticing-winter-moth-in-ma-youre-not-only-one
If you’ ve been managing insect pests of trees & shrubs in eastern and coastal Massachusetts for the last 3 or 4 decades, you’ re likely familiar with Operophtera brumata, also known as winter moth, a springtime geometrid( inchworm) defoliator of oak, maple, and apple but also blueberry, basswood, cherry, ash, white elm, crabapples and others. Tiny, green caterpillars wriggle into the expanding buds of these host plants, damaging flowers that turn to fruit for agricultural crops and leaving shade trees and ornamentals with holes in their leaves. At the height of their outbreak in the late 1990s( on Cape Ann) and early 2000s elsewhere in the state, this equated to persistent, annual defoliation. That is, until 2018 when Dr. Joseph Elkinton Professor in the Department of Environmental Conservation at UMass Amherst, now emeritus, and cooperators converted the winter moth to a non-pest. This was accomplished with a successful biological control program using a parasitic fly, Cyzenis albicans, which is host-specific to the winter moth.
With that historical review in mind, it’ s no surprise that small, light brown moths with fringed wings seen flying about Massachusetts landscapes on cold days from mid-late November through January can easily put observers on alert. Arborists and pest managers in eastern Massachusetts report a mix of springtime inchworm defoliators most growing seasons. Talk of these defoliators has been consistent in recent years, but since November 2025 UMass Extension and other regional groups monitoring tree & shrub insects have received emails, questions, and reports via [ the app ] iNaturalist about suspicious little brown moths flying in Massachusetts and coastal locations in New England. So, what’ s going on with the winter moth population?
2025 Observations Winter moth( Operophtera brumata) and native look-alikes Bruce spanworm( Operophtera bruceata) and fall cankerworm( Alsophila pometaria) all have winged, light brown and variously marked adult male moths that can be seen flying roughly from November through January. This unusually timed activity( for an insect) along with their attraction to nighttime lights can make them very noticeable. For all three species, the adult females are virtually wingless and do not look like a typical moth. They may be found crawling along the ground and at the base of trees. While some geographic trends about the location of the population of each of these species in Massachusetts, particularly for winter moth and Bruce spanworm, are known in the literature- identification to species is not a simple process. Often, this requires a skilled taxonomist who specializes in the identification of moths and has the knowledge required to dissect the males of each species. Even then, adult males of the two species are extremely difficult to distinguish, and DNA analysis is the only known accurate method for differentiating these two species.
Arborists have reported flights of moths in Brookline, Wellesley, Newton, and Sturbridge, MA and in Martha’ s Vineyard, MA as well as Cumberland, RI in November & December of 2025. In the mainland MA and RI observations, groups of 30-50 moths were reported. On Martha’ s Vineyard, in a 3.3 mile stretch, over 525 moths were counted. Over 1,000 reports of possible winter moths, Bruce spanworm, or fall cankerworm have been made via iNaturalist thus far this season across the region. These reports are based on individual’ s observations, not trapping data, and represent an increase in reports from the winters of 2023( n = 463) and 2024( n = 696).
Currently, Dr. Jeremy Andersen, an Assistant Professor in the Department of Environmental Conservation at UMass Amherst, reports that western areas in Rhode Island are experiencing a true winter moth outbreak. These areas are not close to the sites where Dr. Elkinton and collaborators released C. albicans in eastern Rhode Island prior to 2021. Andersen reports thousands of moths caught in traps, indicative of a heightened population. This is very different from the dozens to even hundreds reported in parts of Massachusetts. Efforts to promote Cyzenis albicans, the biological control agent of winter moth, at these outbreak sites in Rhode Island is currently underway in collaboration with Allana Russell from the Rhode Island Department of Environmental Management.
MAA NEWS SPRING 2026 18