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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. |
