Snow Flea

2013 December 11

For something that is supposed to be so common, I certainly took long enough to find one. This is a “snow flea”, tiny little creatures that are known for coming out on top of the snow in the winter. I found it by walking around the house on a sunny day in early Spring (April 14, 2013), and looking closely at the snow for tiny black specks.

They are pretty tiny, this one was only about two millimeters long – just big enough to be visible to the naked eye, but not big enough to easily see details. It could hide by standing on a comma in a standard piece of printed text.

At this size, camouflage is almost pointless, so they are just black, probably to absorb sunlight to warm up while standing on top of the snow.

Even though people call then “snow fleas”, they are actually a variety of Springtail in the class Collembola. The ones that come out in winter are specifically in the genus Hypogastrura, with adaptations to keep from getting killed by freezing. They get called “fleas” because of the way that they jump around, but they are completely unrelated to fleas. They don’t suck blood (springtails are detrivores, eating things they find in the leaf litter), and they don’t even jump using legs, the way that most jumping arthropods do. Instead, they have a little two-pronged spring structure on their abdomen, called a furcula.

They keep it folded and “cocked” under their abdomens, but if something startles them they release the catch on the furcula, and it pops open, flinging them into the air. This is a completely uncontrolled means of locomotion, since the springtails don’t have wings and so can’t guide themselves through the air. So they end up landing somewhere at random, usually upside down, and have to flip themselves back over.

There are obvious problems with using the furcula to jump around, so they mostly just walk and save the jumping for emergencies.

When I was a kid, springtails were considered to be a type of insect, but these days they are in a class by themselves. They are still sometimes grouped together with insects as “Hexapodia”, which are the 6-legged arthropods, but springtails have significant differences from insects. In particular, springtails do not have anything even resembling wings, and they also don’t have the breathing trachea that insects have. Most of the springtails just absorb oxygen through their skins, which only really works if you are pretty tiny. Which is why they are so much smaller than the average insect.

Anyway, springtails are everywhere, you just have to look closely.

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