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Winter 2011

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

February 15, 2011

Snow swarms:

Winter crane flies

Mild days unleash cold-hardy flies

After weeks of freezing weather, a sunny, calm afternoon in the 40s will prompt an emergence of winter crane flies in the woods. About a third of an inch long, the delicate insects resemble mosquitoes -- but without the blood-sucking beak.

Silvery swarms of rambunctious males hover a couple of feet above the ground, each fly bobbing up and down, stitching the air with a bouncy mating dance.

Females spend most of their time on the ground but will briefly join a swarm of males to couple with one of the bouncers. After mating, females return to the forest floor to lay their fertilized eggs.

Winter crane fly larvae live under leaf litter, in caves and in animal burrows. They feed on decaying plants, fungi, dung, even carrion.

The dark brown, short-lived adults can sometimes be seen sitting on the snow, which makes them a much more visible target for insectivorous birds such as wrens.

SOURCES: International Journal of Speleology, Insectsofwestvirginia.net, "Forensic Entomology"

A swarm of winter crane flies