By Declan McCabe
I consider the lack of biting insects and other invertebrates, to be a wondrous gift of the winter season. I can wander unmolested through wood and field absent the attentions of mosquitoes, deerflies, and, God forbid, ticks. And aside from a short list of “usual suspects”, insects are a rarity to be encountered in the winter woods.
This begs the question: where do the insects go in winter? The short answer is ‘pretty much everywhere’. I could also add that they do so in each and every insect life stage; insects overwinter as eggs; larvae/nymphs; pupae; and adults. Where and how each species makes it through the winter season depends very much on the species in question.
Many aquatic insect for example, handle the winter weather by going about their submerged lifestyles as they did in other seasons; just with the addition of an icy glass ceiling. There are even some advantages to cold water conditions. Colder water holds more oxygen, and at least some predatory fish slow their foraging activities in frigid water. Most aquatic insect larvae and nymphs do the bulk of their feeding and growing in winter and emerge as non-feeding adults in the other seasons. Mosquitoes, deerflies, blackflies, and a few others, unfortunately for us, buck the non-feeding trend.
Terrestrial insects employ diverse strategies to weather winter conditions. Mourning cloak butterflies and several other species spend at temperatures well below freezing. After reducing the water content of their bodies by as much as a third and then produce antifreeze compounds such as glycerol or sorbitol to prevent the formation of tissue destroying ice crystals. They hunker down under tree bark or in tree cavities and wait out the deep freeze. In spring, they open their wings, and bask in the sun to get warm enough for flight. Their dark wings and bodies help with the solar heating, and dense hair helps trap the heat.
Monarch butterflies have more of a snow bird lifestyle. Long before the snow flies, monarchs take their own long-distance flights. Following instinctual flight plans, monarch grand children or even great grandchildren of butterflies that left Mexico, make it back to their tropical ancestral homes. And who could blame them? I wouldn’t object to a winter in Mexico!
Our state insect, the honey bee, a European immigrant like myself, has a very different strategy to stay warm in winter. When the mercury takes a dive, honey bees team up to form a winter cluster. A bit like a three-dimensional rugby scrum, winter clusters straddle several honeycombs and in large hives can exceed basketball proportions. As temperatures fall from above freezing to several degrees below zero, honey bee metabolic rates actually increase keeping the bees substantially warmer than the ambient temperature. The bees on the outside of the cluster serve as an insulating layer trapping the sugar-fueled heat.
But not every species can rely on migrating to Mexico or team work for body heat. Some overwintering insects seek warmth more locally. You may have encountered a few, or perhaps more than a few insects trying to make your home theirs to survive the winter chill. Box elder bugs and Asian ladybeetles famously move into structures and we see them coming and going in fall and spring. But let’s not go so far as to call it an infestation; it’s not, and besides, if you disagree you’ll have to disclose it to your real-estate agent when you sell.
A good number of insects spend the winter as eggs that simply hatch into a new generation when the weather improves. There are examples too numerous to mention, but my personal favorite, at least in terms of their parental care, is the gypsy moth. Before the big chill arrives, female gypsy moths lay eggs in dense clusters around the bases of trees. The female uses silk to attach hair pulled from her own body to the egg cluster providing some modicum of protection from the elements. The hairs are irritating to the touch and may also serve against predators. This behavior sounds very self-sacrificing, but life after laying eggs is short for a gypsy moth, so the hairs are better used protecting eggs than adorning a moth corpse. Spring hatchlings use silk of their own making to “balloon” away on the wind, Charlotte’s Web style.
The list of winter pupating insects is also long, but among the more familiar are some members of the swallowtail butterfly family (Papilionidae). The familiar tiger swallowtail and the eastern black swallowtail both sleep away the winter secure in silken pupal cases spun by the larvae. All appears quite in a chrysalis to the casual observer, but the stillness belies the cellular migration that transforms the caterpillar body into a butterfly. This process is driven by daylength and temperature, cues than ensure successful butterfly emergence timing in spring.
And what about those winter wandering “usual suspects” I mentioned above? I took a few winter rambles this year just to see who might be braving the snow. My December trips were a bust as far as insects went, but January yielded dozens of non-biting midges, small winter stoneflies, a cranefly in the genus Trichocera, and an energetic snow scorpionfly backpacking his mate about the place; you can find photographs I took on iNaturalist. The cranefly even mustered a brief flight when it grew tired of me placing it on my glove for a better photograph. What brought such an abundance of mid-winter insect life? I have no idea, but I’m taking it as a good omen for 2021!