Winter in Kansas: wind....snow-covered ground. We ought to be thankful though. It's our cold weather that keeps alligators out of Kansas ponds. And amebic dysentery and tropical parasites can't survive here either. So we don't expect to see live insects outside on the snow in North America. But you can.
That's what makes "snow flies" so unusual. Adult snow flies come out in winter–not in the summer–and walk across the snow in forested areas. The world expert on these little-known flies is a retired entomologist right here at the University of Kansas, Dr. George Byers...he wrote the book on them.
His specimens were mostly collected in the months of October and November, and February and March. Snow flies are wingless; they look a little like spiders as they stomp their way across the snow at the breakneck speed of four feet a minute.
But most of the time snow flies stay underneath the snow. Snow forms a blanket over the warmer earth and shelters it from the bitter cold wind above. When the warm earth melts away the bottom of the snow blanket–which remains propped up by grasses and litter–a thin open space forms a mild little world underneath the snow. That's where Dr. Byers found that snow flies spend much of their life, living in the rodent burrows. It is still too cold for an insect to fly, and wings get in the way–so the snow flies evolved away from their fly ancestors and over time lost their wings.
Now the strangest feature of snow flies is that a few of them wear a necklace! Some of Dr. Byer's specimens had little collars that could be rotated. These donut-like rings were a puzzle until he discovered that the ring contained baby worms. Nematode worms need a way to travel from one rodent burrow to another. The female nematode apparently lays it’s a ring of eggs around the neck of the snow fly when it emerges from its pupal skin. The adult snow flies then provide the baby worms a taxi ride to another area of the forest.
It has been two decades since I first heard Professor Byers eagerly talk about his snow flies. Like any well-taught lesson, it stays with you. And every year, on mild winter days, when I can get to a snowy eastern woodland, I scan the snowbanks for these wingless little insects.
Flies that wear necklaces and walk on snow really do exist.
John Richard Schrock is Editor of the Kansas School Naturalist. The issue on “Snow Flies” is available free upon request from the Biology Department, Box 4050 at Emporia State University, Emporia, KS 66801 and online here.