Winter in the Northern Hemisphere – is there anything more unpleasant? To most entomologists living in temperate climates winter is synonymous with the disappearance of everything they love: insect activity and the pleasant buzz of millions of wings, vibrant colors of plants, warm weather. Our beloved animals have long turned to dust, buried themselves into the ground, or entered a stupor so deep that they might as well be dead. It will be long months before the word “green” re-enters our vocabulary, and both our skin and the ground below our feet breathe a sigh of relief.But as I walked from my car to work this morning, trying with all my might not to expose any unnecessary fragment of my body to the frigid, dry air, I suddenly remembered that there was an insect, a very interesting one, that flourished in this dead season. I first saw it a few years ago in the middle of February on Wachusett Mountain in MA, jumping on the surface of deep snow like a black, shiny flea. It was a snow scorpionfly, a fascinating insect that up that point was only familiar to me from entomology textbooks.
Snow scorpionflies (Boreidae) are fascinating insects that can often be found on snow in temperate forests of the Northern Hemisphere. Their relationships are still somewhat mysterious —traditionally they have been considered a family of scorpionflies (Mecoptera), a group of agile, predaceous insects, but recent molecular and morphological studies suggest that they may be in fact more closely related to parasitic fleas. Regardless of their genetic affinities, these peaceful, moss-feeding creatures resemble little either true scorpionflies or fleas, and both their larvae and adults feed on mosses.But why are they active in the middle of winter? Bodies of all living cells contain a very high proportion of water, which turns into ice crystals when the temperature falls below 0°C, damaging the cell structure and potentially killing the organism. And yet, even in the middle of winter snow scorpionflies are not alone. Many arthropods have evolved physiological adaptations that allow them to survive and be active in subfreezing temperatures. As ectotherms, animals that cannot generate their own body heat, winter insects and spiders must possess the ability to supercool their body fluids in order to remain active in subfreezing conditions. Supercooling, a process that allows them to lower their body temperature to well below the water’s freezing point and still maintain its liquid state, is achieved by the presence of polyhydric alcohols and antifreeze proteins in their hemolymph and cells. Like other winter-active insects, snow scorpionflies take advantage of the fact that most predators that target insects disappear in the cold months, and come out in large numbers to mate. The larger and chunkier female is completely wingless, whereas the male has a pair of strangely modified, scissor-like wings, which he uses to clasp the female’s mouthparts and secure her position on his back during mating. After mating the female uses her long, external ovipositor to lay eggs in clumps of moss, where they will stay dormant until spring.
I have not seen scorpionflies this year, yet, but I will look for them. These animals may be about the size of a pinhead, but for me, in this season, they loom large.
It is not surprising that carrying your eyeballs at the ends of a long broomstick does not make your life any easier, and it has been shown that males who have particularly long stalks must also develop larger wings to compensate for the drag caused by their eyes. This, in turn, supports the idea of the “Handicap model” of sexual selection in these flies – because the long eye stalks make the male’s life more difficult, surely he must be a carrier of some excellent genetic material to be able to overcome the handicap of the gargantuan ornaments.
Update (22 Jan. 13): Thanks to Hans Feijen for identifying the fly species, which turned out to be Diasemopsis fasciata, and not Diopsis.