OBJECT OF THE MONTH - December, 2004

Snow Fly (Chionea nigra)

Chionea nigra collected on a snow bank in Boulder County, Colorado above 9500 feet on April 24, 1952 by W. S. Osburn. UCMC #0000032.

Who would imagine that Colorado is home to a wingless fly that crawls around on the snow during the winter months, but it's true. Chionea nigra is the fly. This species occurs only at high elevations (between 8,500 feet and tree line) in Colorado and northeastern Utah. It has been found on snow during all months from October through April. Although the number of observations in the field are few, we can tell that Chionea does not seem to have a preference for a particular type of snow (fresh powder, frozen granular, etc.), but they are most often collected on cloudy days or in late afternoon.

This specimen (UCMC 0000032) of Chionea nigra is the allotype female, meaning it is the specimen on which the scientific description of the female of this species is based. It measures about ¼ inch long.
Like all flies, snow flies are holometabolus. They undergo complete metamorphosis like a butterfly, with an egg, larva, pupa and adult stage. It is the larval stage that feeds, probably on detritus. The adults are not known to feed. Unlike most flies, however, snow flies do not have wings and therefore cannot fly. Instead, they use their long legs to crawl and are known to leap.
Chionea nigra is a type of crane fly. Most people are familiar with crane flies, which look like giant mosquitoes with a wingspan of 1-2 inches and extremely long legs that dangle as they fly. The snow fly has evolved to a wingless, smaller-sized version that is specially adapted to winter life.
How can an insect be active in the winter months without freezing? Well, several different kinds of insects are able to withstand the cold. The microenvironment provides shelter, and some of insects contain an antifreeze-like substance in their blood.
Next time you are out snowshoeing in the high country of Colorado, look for these small black specks crawling across the snow. You may find a real treat!
More information on snow flies can be found at the following:
Byers G.W. 1983. The crane fly genus Chionea in North America. Univ. of Kansas Science Bulletin. Vol. 52 (6): 59-195.