Snow Fly – Chionea valga

2008 January 19

Last Saturday (Jan. 12), we had all just stepped outside the door when S_ said, “Hey, there’s a bug in the snow!” It was this little fellow, who was merrily scampering across the surface of the snow just like he knew what he was doing:



Honestly, I didn’t know what to make of this. I didn’t even know what order it was in. Was it some sort of earwig? A true bug nymph? Some kind of weird wingless fly? Some obscure insect order that one doesn’t normally see? What was it? So, I caught it, and put it in the refrigerator to warm up[1] while getting getting apparatus organized, and took some pictures.

Then, at a complete loss, I submitted the pictures to Bug Guide, and somewhat to my surprise there were two possibilities suggested right away: (A) Snow Scorpionfly, family Boreidae; or (B) Snow Fly, genus Chionea. It turns out that both of these completely-unrelated types of insects (neither of which I had heard of before) have developed the same general lifestyle: the larvae live somewhere in the leaf debris or topsoil or who-knows where[2] over the warm part of the year. Then, after the snow falls, the adults come out and stride over the snow looking for mates and a good place to lay their eggs. The question is, which type is it?

Well, the key giveaways are that this specimen had minimal antennae, as can be seen here:


and its vestigial wings were in the form of “halteres”[5], which is a trait of flies (Diptera).


This narrows it down to being the snow fly, because snow scorpionflies have long, distinct antennae, and their vestigial wings lie flat instead of being halteres. So, it is pretty firmly identified as the Chionea snow fly. Based on the antenna length, Dr. Chen Young of the Carnegie Museum of Natural History identified it as Chionea valga. Further, we can tell it is a male, because of the claspers at the tip of the abdomen:


The females have more of a straight ovipositor, the males use these pretty startling-looking organs to hang onto the females during mating.

If you are looking for poorly-studied insects, these guys are right up there. This article from the Kansas School Naturalist magazine is a pretty good summary of what is known about them (the figures that the article refers to are here). The first surprising thing is that snow flies are most closely related to crane flies (those things that look like huge, clumsy mosquitoes with enormously long legs that normally fly around in the summer). If I mentally blot out the wings from a crane fly, I can see where the snow flies are actually very similar, but still, it wasn’t an identification that I would have made on my own. That’s actually one of the big problems in sorting out the life history of snow flies — their larvae look like any other crane fly larvae, so if you find one in the wild there’s no real way to figure out that it isn’t the larva of one of the much-more-common winged crane flies.

The big question is, why do the snow flies emerge in the winter and run around in the snow, while all other right-thinking insects are dormant in one form or another? Well, the big advantage is, all other right-thinking insects are dormant in one form or another. Which means that they aren’t prowling around looking to eat the snow flies, who have the snow fields pretty much to themselves. Between the spiders, the dragonflies, the insectivorous birds, and the bats (among many others), the summer ground and the summer skies are very dangerous places for a crane fly. The snow flies neatly avoid all that, by merely adapting to the cold.

Merely (Snort!)

The cold adaptation is actually pretty extensive. First off, they had to avoid freezing. This means that they have significantly altered biochemistry to allow them to not only avoid freezing in the ice and snow, but still be able to function when their body fluids are supercooled below the freezing point of water. As a result, they don’t come out when it thaws, because temperatures above the very low 40s are too hot for them[3][6]. They only really run around when it is, literally, freezing outside.

Second, they lost the wings because they had no need for them. Insect wings depend on muscles being able to drive them very fast, and insect muscle only can manage the fast-twitch thing when they are quite warm. Snow flies are never warm, so they’d never be able to drive the wings anyway. They’d be so much dead weight (and a hassle during the part of their life where they live in the leaf litter). Eliminating the wings also eliminated the muscles that would have driven them, freeing up some more space in the body for extra eggs in the females.

Third, the legs are a lot more robust than average crane fly legs, making them pretty strong walkers. They are therefore able to stride confidently across the snow, looking for mates. Of course, as you might imagine the odds of finding a mate are not that huge, so there’s none of this fooling around with mating displays, or males fighting over a female, or extended courtship, or anything like that. They find each other, they mate immediately for maybe 30-70 minutes, and then she goes off to lay her eggs[4].

As for economic value or impact, well, they probably have none. They aren’t common enough to play a big role in the ecosystem, nothing much is around to eat them, and we don’t even really know what they eat anyway. But aren’t they cool?

[1] Yes, it was actually significantly colder outside than in our refrigerator, so he became warmer and more active during a procedure that I usually use to try to slow insects down.

[2] There is actually not a lot known about either of these types of insects. The snow scorpionflies are at least known to eat mosses and such that they find under the snow, but nobody really even knows what the snow flies eat. They have evidently never been successfully reared in captivity.

[3] This made it very hard to photograph, let me tell you. When I got it on the microscope stage, it ran around frantically almost the whole time, staying still for no more than a couple of seconds at a stretch. If I hadn’t had a cover glass over my petri dish, it would have gotten away for sure.

[4] Because, really, given the difficulty of surviving in the snow, the mere fact that they are out there and still moving around is a strong signal that they are strong, healthy, and therefore suitable mates. They’ve proved everything they needed to prove just by being there.

[5] A note about insect wings: The basic insect body plan has four wings, a front pair and a rear pair. In the true flies (Diptera), the front pair of wings are the only ones that are actually used for flight, the rear pair are reduced to a couple of little nubbins that are basically a ball on the end of a stick, called “halteres”. The halteres evidently act something like balancing gyroscopes, and help to make true flies the strong, maneuverable fliers that they are. For some reason the snow flies have completely lost their flight wings, but kept the halteres for some obscure, as-yet-unknown function.

[6] This brings up a possible background for science fiction novels that I’ve been noodling around with: I think that a big part of the reason why we don’t see really seriously cold-adapted organisms (as in, plants that can grow on glaciers and things like that) is that the cold parts of Earth have too severe of temperature swings. Like this fly: it can manage down to probably 20-25 deg. F, but only at the cost of dying horribly at around, oh, maybe 50 deg. F or so. It realistically can’t adapt to much colder temperatures, because the degree of alteration of its metabolism would mean that it would never make it through the summer. This gives us the situation we have now, where the poles outside of the seas are practically lifeless because the cold kills any warm-adapted organisms in the winter, while the warmth kills the cold-adapted ones in the summer. Now, if the Earth had zero axial tilt, so that the temperature swings at the poles were practically zilch, there would be some incentive for plants and animals to seriously go the antifreeze route, maybe using either ammonia/water solutions or concentrated brines for their intercellular fluids.
So, picture this: an earth-like world, with an axial tilt of no more than maybe a degree or two, and therefore no seasons to speak of. Maybe a bit cooler than Earth so that it drops below freezing right around 45 degrees latitude. Around the equator, we would have water-based organisms more or less like what we have on Earth, but at the north pole, we could have a niche for plants that are based on ammonia-water mixtures, letting them keep growing down to some really ridiculously low temperature (but completely unable to survive at what we regard as room temperature). Meanwhile, the south pole is completely isolated from the north pole cold-climate ecosystem, so it could independently develop salt-brine-based plants. Voila! A world with three completely independent and mutually incompatible ecosystems! Now, if only I were the sort of person who could think up plots, and not just settings, maybe I could write about this . . .

3 Responses leave one →
  1. Lauren Thibault permalink
    January 19, 2008

    That is bloody amazing! I haven’t even ever heard of those.

    I know you aren’t one for catching and killing (normally I am not either) but I would love to examine one up close or even add it to the museum collection. I understand if you don’t want to but I figured there was no harm in asking.

  2. Lauren Thibault permalink
    January 19, 2008

    By the by – Lauren Thibault = Serendith on LJ

  3. January 19, 2008

    Sure, I can try to find a specimen for you. Since we found this one by accident right in our driveway, I doubt that they are particularly rare. It’s probably too cold for them right now (it’s only 2 deg. F at the moment), but now that I know that there are insects out in the snow other than springtails, we’ll probably go out to see what else is there next time it gets up close to thawing.

    Speaking of which, what’s the best way to preserve a specimen for mailing?

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