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Hard to Fly Right

The trials of winter



"Hey Jim," my email read. "How about a Source article describing the nature and intent of winter flies? They come into our houses—fly slow and stupidly and do not feed—and within a day or two, they die. When they keel over, they seem almost completely dehydrated and they actually crumble to dust and body parts when you try to pick them up. Why don't they stay outside and just die there? Best wishes, Philip."

So, what about those "winter flies?"

To begin with, it is probably impossible for a common house fly to die of cold outside in the winter, even at 30 below zero. They are similar to many of our wintering butterflies and other insects and have "blood" (it's not like ours, though), which becomes antifreeze in winter—the colder it gets the better the antifreeze.

Many flies, however, become trapped in our houses at the end of summer, and as Philip and many of you have noticed, most of them end up dying in the comfort and "safety" of our warm home. That's because their physiological time clock (set by the length of daylight—and perhaps by the angle if the sun) has put them into an "outside" hibernation mode.

At the end of summer, instead of using the food they ingest for mating and laying eggs, they have instead put on a layer of fat that will keep them fueled up through the long winter hibernation. But being in a warm environment near the wood-stove, or in the kitchen, keeps their "blood" flowing, which prevents them from going to sleep, so they use their winter fat reserves for flying about.

Bad news: Because we do not leave much fly food lying about in winter, and further, the house environment is a lot cooler than summer, the flies' digestive system will not operate efficiently, and, well, there you go. Sadly, they starve, dry out and fall apart.

It would be the same way for bats and tortoiseshell butterflies if they got stuck in the house over winter and were forced to use their fat reserves; they wouldn't make it to spring either. Mourning cloak and tortoise- shell butterflies are outside sleeping under woodpiles, logs and otherwise out of direct cold and snow where they'll be OK if they're left alone.

On warm days in February or March it is not uncommon to see a mourning cloak or tortoiseshell out flying about, building up oxygen supply—but it's a bit dangerous, as there is a fine balance between fat use and oxygen demands.

Unlike insects, bats have blood similar to ours—it DOES NOT turn to antifreeze; the thin-skinned species have gone south, while "our" bats have settled into dark areas with stable temperatures above freezing where they will use their fat reserves to safely sleep through the winter. That's why some of the lava tubes near Bend are closed to the public, so bats can survive the winter.

But back to the flies. Another problem for the ones trapped in our houses for winter is predators. Yes, those lovely little spiders that you discover in the sink, bathtub, or running out from under the bed—you know, the ones you're blaming for welts you can't explain—well, they eat flies. Sheet web spiders are elegant fly-catchers and probably dispose of many flies long before they are seen flitting about, dying and falling apart as Philip has noted.

"Outdoor" flies, such as mosquitoes, robber flies and crane flies, die in winter, and leave their eggs to start the next generation the following summer. However, gnats, which are also technically flies, have an astounding behavior in winter.

Some species of gnats seem to wait for winter to prepare for mass breeding orgies. From October to March, on any day when the temperature rises to above 60 degrees, gnats will take advantage of the situation and form a mating swarm to get a head start on the rest of the insects. It's probably good strategy, there are very few birds out looking for insects, bats are sleeping, and (most) predatory insects are not about, so they have the world all to themselves.

And then there are the snow scorpion flies you can find on surface of the snow in late winter around Bachelor and other parts of the High Cascades in winter. But, they are neither scorpion nor fly.

Snow scorpion flies are dark, funny-looking, six-legged insects with a "beak," and are in the Boreidae family. They're pretty small and there are only around 30 species, all of which are boreal (high-altitude species).

Recent research by the scientific hair-splitters suggest the boreids are more closely related to fleas, with the wings reduced to bristles or absent. Some people think they actually resemble scorpions because of the pointed tail-end, but not this old man; they appear to be something closer to a grasshopper with a modified face.

They are most commonly active during the winter months, toward the transition into spring when mating takes place (I've seen 'em makin' whoopee in February up near Bachelor); and they go through complete metamorphosis: egg to larva, which feeds on mosses, to pupae to adult.

The adults will often disperse between breeding areas by walking across the open snow, and the males use their bristle-like wings to help grasp the female while mating. How that behavior got someone to give it the name snow scorpion fly is beyond me.

PLEASE don't pick one up. Just be content to watch it scamper by. Better yet—shoot a photo and leave it be; they are so well adapted to the cold environment that just holding it in your hand will kill it.

Now all you have to do is remember to send me that photo.

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