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Fleas in winter?

February 11, 2009
By Richard Gast, Franklin County Cornell Cooperative Extension

It's just a matter of time until I receive panicked calls about a sighting of scores of little black specks jumping around on the snow

in people's yards. Are they fleas? Do they bite? Are they dangerous?

There must be a hundred thousand of 'em! They're everywhere! What are they?

What are they, indeed? Commonly called "snow fleas," and wrongly associated with dog fleas, these acrobatic little critters are actually not fleas (order Siphonaptera) at all. Both are small and can jump, but the similarity ends there.

Unlike dog fleas, snow fleas are harmless to pets and people. They do not bite or transmit disease and they won't get into the house or

contaminate foodstuff.

In fact, snow fleas are quite beneficial. They consume bacteria,

microscopic algae, rotting vegetation and fungi, such as leaf mold.

And, at the same time that they are helping to keep bacteria and

fungi under control, they are building soil by breaking down leaves

and other organic matter.

Snow fleas are arthropods (a phylum of invertebrate animals with

jointed legs and segmented bodies). The actual number of living

arthropod species is probably in the tens of millions. Some better

known examples are crabs, spiders, moths, ants and bees. They belong

to an ancient group of insects called Collembola. More commonly known as springtails, Collembola date back to the middle Paleozoic era (about 400 million years ago), when the first true plants began to

appear upon land. We know this because anthropologists have found

their remains amid fossils of those first land borne plants.

Collembola could very likely be the most common form of terrestrial

insect in the world, with more than 2,000 species in North America alone.

And the snow flea (Hypogastrura nivicola) could very well be the most numerous of all the springtail species on Earth. There is debate

within the scientific community, however, as to whether springtails

are even insects at all, since true insects have eleven abdominal

segments and springtails have only six. What's more, they do not

undergo metamorphosis of any kind.

Some scientists believe that Collembola should be classified as

crustaceans. Others believe that because of the many differences in

anatomy and genetics, they deserve to be in a class all their own.

They lack true eyes, do not possess wings and have, protruding from

their abdomens, a "spring tail," called a furculum, (after the Latin

word for fork) which is held in place by two tiny hooks. When these hooks are released, the tail springs open and the snow flea is

catapulted into the air.

Springing is the means by which springtails evade predators such as

ants, beetles and mites. A sticky extra limb or appendage, called a

collophore, enables springtails to adhere to surfaces such as the

undersides of leaves. This appendage is, in fact, how Collembola were named, by combining the Greek words "coll," or glue, and "embol," meaning wedge. This appendage is also a ventral tube that is used for drinking or, more accurately, for absorbing water from the soil, and for breathing. There is debate as to whether or not it is used for excretory purposes, as well.

Most insects are cold blooded and, therefore, inactive during the

winter. Springtails, however, as a result of a unique ability to utilize proteins in their bodily fluid to actually inhibit freezing, have an extraordinarily high tolerance to the cold, which allows them mobility at sub-freezing temperatures. They spend most of the winter deep in the relative warmth of the soil but, when the snow starts to melt and conditions are right, they travel in large numbers, through breaks in the snow pack, to the surface. Once at the surface, they feed and mate. Their black color allows them to absorb heat from the sun. Snow fleas thrive on exposure to the combination of warm sun and cool air.

As spring approaches and the sun heats up the air, trees too, absorb

heat from the sun. This, in turn, causes the snow at the bases of the

trees to melt. As the snow melts, the adult springtails seek out the exposed areas of ground beneath the trees, in order to deposit their eggs amid the leaf litter and debris found there. When they hatch, the young snow fleas are less than a millimeter long. They mature throughout the spring and summer, becoming sexually active adults in the fall and remaining sexually active from November through March.

Springtails are not nearly as obvious when congregating on the forest

floor, as they are when seen upon the stark background of the snow.

Nonetheless, when there is no snow on the ground, these tiny, harmless soil builders can be found teeming upon decomposing leaves and other debris in numbers totaling a thousand or more per square yard, millions per acre.

Snow fleas are easily found on melting snow, especially as we get

into late winter and early spring. And although it may be just a little bit early, they are very likely in your yard right now. So, if you're of a curious nature and enjoy the cool air and warm sun as much as springtails do, the next time the sun is up and the snow is melting, why not take a short journey of exploration to a snow bank near you?



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