Ask The Entomologist

Winter Crane Flies: widespread and little-known

As I was walking over to my in-law’s place one chill and sunny afternoon, I happened to spot a fly. A gangly, long-legged fly, seeming to bounce up and down in the brisk winter air. Unlike the cluster flies lining the edges of our ceilings, this one was fairly active, despite the temperature.

Naturally, I snatched it out of the air for a better look.

It wasn’t just any fly – at first glance it appeared to be a crane fly… but parts of it weren’t quite right. It had simple eyes in the center of its forehead, something absent in true crane flies. Nor was it quite the right size – it’s perhaps 1.5 to 2 times the size of an average mosquito, whereas crane flies can be far larger, and with a broader leg-span. It was a winter crane fly.

If you look closely, you’ll find that the winter crane fly, like its true crane fly relatives,
does not have stabbing mosquito-like mouthparts.

While not true crane flies, winter crane flies are close relatives, and both develop in similar areas and eat similar foods. Wet spots on land, perhaps along a stream or seep, are perfect for a growing winter crane fly maggot. True crane fly maggots (often called “leatherjacket slugs”) prefer to swim in the stream itself, and can make excellent fishing bait. Both types of maggot like places that have plenty of moist decaying plantstuff to feed on.

Interestingly, winter crane flies have been documented gathering in large numbers underground… both here and in the Old World. I observed this in a number of western Kentucky stream caves while I was studying a group of eyeless cave beetles, but little has been written on the behavior in this organism. I wonder if it could be similar to how mosquitoes overwinter in caves…

To my surprise, Winter Crane Flies have become invasive in Antarctica in the past decade… it’s thought that they started out by colonizing the polar scientists’ sewage treatment plant, and escaped to the outside. Impressive for a wee beastie that is only active for a couple of months out of the year here. Of course, the Winter Crane Flies invading Antarctica have much less competition than those around here!

What is a pest in one place may be entirely harmless in another.

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