Snow Fly? What the Heck Is a Snow Fly?

Or, In Which I Discover Snow Flies and Am Once Again Amazed by How Weird the World Is.

On Valentine’s Day, while setting up luminaries for a romantic candlelight snowshoe hike, I discovered this little creature walking across the surface of the snow.

I’ve posted photos of unexpected winter arthropods before, but those spiders and caterpillars were not this active – when placed on the frozen surface of the snow they quickly stopped moving. What the heck was with this thing, then? Since when do insects walk around in below-freezing temperatures like it’s nothing?

Thanks to the good folks at BugGuide, I now know that this is a snow fly, genus Chionea. (If you see the little round knobs on its back in the photo, those are structures called halteres that are unique to flies.) It is a wingless fly (who knew there was such a thing?) and the only time it’s ever really seen is walking around on the snow in the winter. It’s presumed that being active in the winter helps it avoid predators, and it does this by having antifreeze in its bodily fluids. SERIOUSLY, THIS IS CRAZY, WTF IS THIS THING. Actually it gets even weirder – possibly the only thing weirder than being a wingless fly with antifreeze for blood is being a parasite that specializes on wingless flies with antifreeze for blood, and according to Wikipedia there are nematodes that do just that.

You guys, nature will never stop making me freak out.

15 replies on “Snow Fly? What the Heck Is a Snow Fly?”

Actually, I was joking about the snow flies eating snow fleas, but I’m glad you looked it up, now I know. From what I understand, no one is quite sure what snow fleas (springtails) eat either. Some speculate that they eat algae that grows in the snow. You have to love nature, where every answer unlocks another thousand mysteries to be answered.

So cool! I just found your blog, and as a new field botanist originally from the great state of Wisconsin (now in NW Indiana), with two brothers-in-law at Point, I am very much enjoying reading your posts! You have such an enthusiastic sense of wonder, and I love hearing about all the interesting things that happen in the northwoods! I look forward to reading more!

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