Snowfleas are such remarkable little arthropods that they merit at least an annual post. The recent warm weather brought them up out of the leaf litter to the surface of the snow, where they constantly hurl themselves from one spot to another. If you don’t mind getting your knees wet, you can watch as snowfleas tuck their head down and catapult themselves through the air. Just before launching themselves, the snowflea everts three anal sacs from its anus. When the snowflea lands, these sticky appendages act like automobile air bags, absorbing the shock of landing as well as preventing the snowflea from bouncing around. There may be another function that they perform, but it is not known at this time what that might be. While there are many genera of snowfleas, only species in the genus Hypogastrura possess anal sacs.
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We tend to associate snow fleas, a type of springtail, with winter, as that is when we can easily see their tiny black bodies against the white snow. However, these insects don’t magically appear when it snows – they are in the leaf litter and soil all year round. Snow fleas are considered to be one of the most numerous land animals on earth, with several hundred thousand inhabiting a cubic yard. Even so, it was with amazement that I found several piles of snow fleas at the base of my garage door this morning – it’s the wrong time of year, and most of the individual snow fleas were not scattered apart from each other. Several solid black patches of snow fleas, one patch measuring roughly 6” by 2 ½ ”, piled 1/8” high, had appeared overnight. Something about the warm, humid air this morning may have caused them to leave the safety of the forest floor and for some unknown reason gather in piles on the cement. Once the garage door was raised, the piles disappeared within five minutes, as each tiny snow flea catapulted itself several inches away and disappeared into fallen leaves.
Snow fleas, a species of springtail, are neither fleas nor insects (though, like insects, they are arthropods). During most of the year they live in the soil and leaf litter, consuming fungi and decaying vegetation. On warm winter days they appear on the surface of the snow, and are often described as “pepper on snow” due to their black color and tiny size (1 – 2 millimeters long). Although they lack wings, they have two tail-like spring projections, or furcula, which are held like a spring against the bottom of the abdomen by a kind of latch. When the snow flea wants to move, the furcula springs downward, catapulting the snowflea as far as 100 times its body length. I observed something recently which I have neither heard nor read about, and that is a four-pronged pinkish appendage which emerges from the tip of the snowflea’s abdomen just before it flings itself to another spot. At all other times, this structure is withdrawn into the abdomen and is not visible. Photographing this structure during the split second it is extended was quite the challenge, and I would love to hear from anyone who might know its function. NEWS FLASH – mystery solved by Charley Eiseman, author of TRACKS & SIGN OF INSECTS: Those three (not four) structures are anal sacs. According to Frans Janssens, “just before hopping in the air, three sticky vesicles are everted from the anus: they serve as a kind of sticky safety bag that prevents the specimen [from] bouncing around when it lands after the jump.” ONE LAST UPDATE: from Dr. Ken Christiansen, Professor Emeritus of Grinnel College, AKA Dr. Snowflea, who reports that these anal sacs are only found on species within the Hypogastrura genus, and that their function is unknown.