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Winter's Wonders Come in Small Sizes

One of the things I look forward to every Christmas vacation is spending a little time cross-country skiing in an area of the San Juans that is seldom visited by other people. Winter's beauty, the quiet isolation, and the opportunity to ponder life make the experience refreshing and rejuvenating for me. A good friend shares the same sentiments and so we find ourselves making parallel tracks in unbroken snow when the new year is scarcely a few days old.

            We stop in a small opening surrounded by aspen trees to listen to the silence and take in the picture-perfect scene.  I take a mental panoramic shot because I want to remember how perfect the albescent snow makes the area look. What can be more pure than untrodden snow at ten thousand feet miles from the nearest town?

            Momentarily considering how refreshing a mouthful of this snow might be, I study the snow's surface next to my ski. Suddenly, I am struck with the realization that the snow may not be so clean after all! Looking closely, I see tiny black specks, thousands of them, all over the surface of the snow.

            My picturesque image of the area dissolves and I wonder if the black specks are soot particles that have drifted through the air from some smokestack hundreds of miles away and settled on the snow. Perhaps, though, the specks are natural--clumps of pollen or spores--and I bend over for a closer look. Now my eyes begin playing tricks on me. Some of the black specks suddenly disappear. Others seem to instantly change positions. Scooping up a handful of snow, I watch the black specks very closely and realize they are alive. Most are still, some crawl very slowly, and occasionally, one is instantly propelled out of the snow in my hand landing who knows where. They are snow fleas.

 What are Snow Fleas? 

            Snow fleas are not really fleas, but belong to a group of primitive insects called springtails (Collembola). They are found on every continent, and are the only insect (with the possible exception of a few bird parasites) that can be found near either pole. Typically less than a millimeter long, they look like black, oval-shaped specks to the unaided eye. They are most easily noticed when they gather by the thousands in a small area to feed on pollen, spores, algae, or bacteria on the surface of the snow. Despite their name, they cannot harm people or pets, and actually play an important role in building soil. 

Olympic Jumpers

            Snow fleas, like all springtails, have an unusual appendage (a furcula) that folds under the abdomen and can be used to suddenly propel the insects several inches. This means a snow flea can jump about one hundred times its own length. That is a feat equivalent to a grown man jumping the length of two football fields! 

Living in the Snow

            All insects are exothermic, which means that their body temperature (and thus activity level) depends on the temperature around them. With most insects, cold temperatures cause a state of inactivity. Watch any anthill during late summer and you will notice that the ants are more active during the heat of the day and less active as the temperature drops towards the evening. So how can snow fleas survive in the snow?

            Because of their black color, snow fleas easily absorb heat from the sun. They are often most active when the sun is shining on the snow and the temperature is near freezing. It is possible, too, that the snow flea's metabolic chemistry is different from other insects, functioning best at temperatures just below freezing. There is a big advantage of being active in the winter--there are very few predators out and about during this time of year. 

Snow Flea Life Cycle

            During winter, as a tree absorbs heat from the sun, the snow will often melt away from the base of its trunk. Snow fleas will follow this path down to the leaf litter where they will lay their eggs. The young hatch in the spring, mature during summer, and are adults by the following fall. 

Really an Insect?

            Not only is the snow flea not a flea, but it may not even be an insect. After studying the springtail's primitive anatomy in detail, many scientists now consider the creatures to be a special kind of hexapod. Hexapods are predecessors of insects from which insects are believed to have evolved.

Other Snow Bugs

            Although certainly the most abundant, snow fleas are not the only insects (hexapods?) that thrive in the snow. There are half a dozen other insects that might be seen scurrying across the snow, one of which we also noticed on our outing. The wingless crane fly (or snow fly) is a spider-like insect about the size of a pencil eraser. With its relatively long legs it can travel rather quickly across the surface of the snow. The snow fly is most active at temperatures close to but below freezing. Its body fluids (insects don't have blood) contain glycerol, a chemical similar to antifreeze. Surprisingly, no one has been able to discover what snow flies eat.

            Winter provides a great opportunity to get out and enjoy nature. Borrow or rent a pair of snowshoes or cross-country skis and head for a secluded area. Take some time to sort out the tale that animal tracks tell in the snow. Enjoy beauty that cannot truly be captured with a camera. Listen to the refreshing sound of complete silence. But every once in a while, bend down and look the snow over closely. Sometimes nature’s wonders come in small packages.          

Large snow flea image from Queens University.  
© 1997, 2006  Dirk Oden  
 

This site was last updated 03/13/07