November always seems like a strange time to see insects. It seems even more bizarre when we experience nights that are at or near freezing temperatures and moths are still active. There are only a few moths that can do this, some “good” and some “bad,” but it is an interesting adaptation. Their purpose for hanging around for so long is that most of their predators have already left our area: bats have gone into their winter hibernacula and many songbirds have migrated south. So who are these late moths? Let’s take a look at two that you may have noticed recently:
Bruce Spanworm (Operophtera bruceata)
Our native late flying moth is often considered a pest. It is known for being a native defoliator, often causing damage to our deciduous trees. This usually happens early enough in the spring that trees can refoliate, but when it happens during a drought year, it can severely impact sap production. Luckily, as a native part of our ecosystem, their populations are kept minimal, thanks to natural controls like parasites, predators and disease.
Winter Moth (Operophtera brumata)
There is the non-native moth you could see flying around. Winter Moths, native to Europe, were originally introduced to North America via Nova Scotia sometime before 1950. This species unfortunately does not have any native parasites or predators here and can therefore cause a lot of damage.
A big problem is that Winter Moths look almost identical to the native Bruce Spanworm. They cannot be identified in the field and can only be separated by examining the male genitalia (not easily done) or, as the biologists studying them like to phrase it: “sequencing the mitochondrial cytochrome oxidase subunit 1 (COI) gene.” Winter Moth has been documented along coastal Maine, from Kittery to Bar Harbor:
The reason I point this out is that even if you are seeing a moth flying around in November, you do not necessarily have to worry about a Winter Moth outbreak. Many people respond to outbreaks with pesticide use or tree removal, which might not always be necessary and could have adverse impacts on native wildlife.
If you’d like to learn more about these moths, a full life history for Bruce Spanworm, including how it got that funny name, is available here.
Also, the Maine Department of Agriculture, Conservation and Forestry has this article on Winter Moths, which includes information on controlling their populations and a parasitic fly that could be a safe answer.
Literature cited: Elkinton, J., Boettner, G., Sremac, M., Gwiazdowski, R., Hunkins, R., Callahan, J., … Campbell, N. (2010). Survey for Winter Moth (Lepidoptera: Geometridae) in Northeastern North America with Pheromone-Baited Traps and Hybridization with the Native Bruce Spanworm (Lepidoptera: Geometridae). Annals of the Entomological Society of America,103(2), 135-145.
A Maine native, Doug grew up in Hollis and graduated from the University of Maine in 2011. Throughout college Doug worked at Scarborough Marsh Audubon Center and was hired as Maine Audubon’s staff naturalist in the summer of 2013, a long time “dream job.” In his free time, Doug volunteers as one of Maine’s eBird reviewers, is the owner and moderator of the ‘Maine-birds’ listserv and serves as York County Audubon board member and Secretary of the Maine Bird Records Committee.