With creative adaptations to survive the cold
Winter may seem like an odd time to think about moths. Most adult moths die in the fall, leaving the next generation to overwinter as either eggs or pupae in a state known as diapause. However, there are actually a few specially adapted species of moth that remain active during the winter months and can be seen flying around on winter nights.
In a 1987 Scientific American article, noted naturalist Bernd Heinrich described how certain species of owlet moth remain active even when winter temperatures are near freezing. When the moths are at rest, their body temperature drops to that of their surroundings and they enter a state of torpor. In the daytime, to avoid being seen by predators, they hide under leaves that provide insulation. But when night falls, and they need to search for food, they must raise their body temperature in order to use their flight muscles – and they do this by shivering. During long flights, they have to stop and shiver in order to warm up again. And what are they eating in winter, you might ask? The nectar of the winter-blooming witch hazel shrub!
Another moth that’s active this time of year is our native Bruce spanworm moth, as well as the very similar but invasive winter moth.* The winter moth is on the rise locally and is regularly seen on the Bristol peninsula. The Bruce spanworm moth is not as destructive as the winter moth since, as a native, it has more natural predators locally that keep its populations in check.
The two species are very difficult to differentiate, looking much alike and having similar life cycles. In both species, it is actually the adult males that can be seen flying from late November to January, and they are sometimes attracted to lights. The females are small, gray and flightless. They crawl around the base of trees and release a pheromone to attract the males. After mating, they lay eggs in bark crevices and lichen. The eggs hatch in the spring when temperatures warm. The larvae then climb tree trunks and burrow into leaves and flower buds, consuming them as they go. once mature, the larvae spin silk and ‘balloon’ to the forest floor where they pupate in the earth between June and November.
Insects have been evolving for more than 480 million years, so perhaps it should not surprise us that they have such remarkable and specific adaptations. Nonetheless, it does always seem extraordinary to see any insect active in winter!
*A Note About Invasive Winter and Browntail Moth Management
Images of the invasive winter moth, an overview of the species, instructions on how to report it, and management resources are available on the Maine Forest Service website.
Browntail moth is another invasive pest getting a lot of press these days. This February, the Maine Forest Service launched “Browntail Moth Awareness Month” with a wealth of information about this invasive species and resources for its management. In recent years, browntail moth have been spreading north and west into Maine, and many people have a strong reaction to toxins in their “hairs” or setae (the proteins are not the same as mammal hairs). These toxins can cause a serious rash where they come in contact with skin, or even respiratory issues if the hairs are inhaled. The moths are also destructive, affecting the health of trees that have been repeatedly defoliated by the caterpillars.
Winter is the best time to destroy browntail moth nests and reduce populations near homes. This article on WGME News offered good information as well as a schedule of upcoming programs about browntail moths and management options. If you have a significant problem with these moths in your area it may be useful to share this article, and the link, with your neighbors.
Management of invasive insects is complicated and often comes down to trying to do the least harm. The vast majority of moths in Maine are critical pollinators for native plants that sustain other wildlife, or their soft-bodied caterpillars are precious food for birds foraging for their nestlings. They are an important food source for other animals, including our at-risk bat population.
Fortunately, there are more and more tools available to help us in this regard. Certainly protecting the trees of our forests, especially the oldest trees that are the most fecund, have the best genetics, and provide carbon sequestration and habitat, is critical. In the process of deciding how to best manage invasive insects, we must also consider our relationships to other invertebrates and the environment as a whole.
Photo: Bruce spanworm moth by Ronald S. Kelley
