It’s hard to believe that flies are not only active but mating now, given the snow and low temperatures that Vermont is still experiencing, but these two flies were perched atop coyote scat doing just that. They are in the Heleomyzidae family, whose members are often found in dark or cold places, and are most likely to be encountered in the spring or late fall. There are species associated with caves, mammal burrows, carrion and birds’ nests, in addition to scat.
Stoneflies spend the larval stage of their life in streams, but as adults they are terrestrial. When the larvae mature, they leave the streams they grew up in, split their larval skins and emerge as winged adults, ready to mate. Most species mature in warmer months, but there are two families, referred to as winter stoneflies, that emerge at this time of year, perhaps because of the scarcity of predators. You can often find these cold-hardy stoneflies crawling around on top of the snow near streams.
If you’ve walked in New England woods recently, chances are great that you’ve noticed light tan moths with a one-inch wing span flitting about — an odd sight for this late in the year. These are male Bruce Spanworm Moths (Operophtera bruceata), also called Winter Moths, as the adults are active from October to December. They belong to the Geometer family of moths, the second largest family of moths in North America, which includes many agricultural and forest pests. The males are seeking wingless, and therefore flightless, females to mate with. Eggs are laid in the fall, hatch in the spring, the larvae pupate in the summer, and emerge as adult moths in the fall. Bruce Spanworm larvae periodically defoliate hardwood trees, preferring the buds and leaves of sugar maple, American beech and trembling aspen trees.
What happens to insects this time of year? A few remain active, such as snow fleas, and some, like monarch butterflies, migrate, but the vast majority of insects overwinter in New England. The insects that stay here are susceptible to freezing due to the fact that they cannot control the temperature of their body. Some insects, such as woolly bear caterpillars, can tolerate having ice form in their tissues, but most insects go into a state known as diapause. When the days start getting shorter, these insects reduce the water content of their body, as water freezes at a high temperature compared to other liquids, and replace it with glycerol, which acts like antifreeze, protecting them from freezing. (Due to technical problems which hopefully will be resolved soon, I am unable to include a photograph with this post. My sincere apologies.)
Rarely do you see or hear about honeybees attempting to construct a hive outdoors that isn’t inside a hollow “bee tree” or in a rock crevice. Occasionally they do attempt it, but as the empty cells in this exposed comb attest to, honeybees aren’t likely to make it through a Vermont winter without some shelter for their hive, even a winter as mild as the one we just experienced.
It always comes as a surprise to see tiny creatures moving nimbly over the surface of the snow. However, there are quite a few insects and spiders that do, thanks to the glycerol that they produce in their body fluids that keep them from freezing. The Snow Fly (Chionea sp.) is wingless, probably because at sub-freezing temperatures, it would be very hard to generate enough energy for maintaining flight muscles. They (along with other flies, mosquitoes and gnats) do have two vestigial wings called halteres, the little knobs on the fly’s thorax. They inform true flies about the rotation of their body during flight, and are thought to act as sensory organs for the flightless Snow Flies. Throughout most of the year Snow Flies can be found in leaf litter, but come winter the adults emerge, mate and lay up to 200 eggs. The lack of predators such as dragonflies and most insect-eating birds makes winter a relatively safe time for Snow Flies to be out and about. Their life span is about two months, during which time they drink by pressing their proboscis against the snow, but don’t eat. (Snow Fly in photograph is a female, measuring less than ½”.)