On a nice day in winter, one can sometimes see little dark spots on the surface of the snow. But unlike most dark spots, these jump! They can jump distances many times longer than their own bodies. It’s a rather uncontrolled leap, almost random in direction and the landings are awkward, often upside down or head-first.
These are the so-called “snow fleas.” A total misnomer — they are not fleas at all!
True fleas are bothersome parasitic insects; they jump using their hind legs. Snow fleas and their relatives are springtails, and they jump using a special gadget near the end of the abdomen. It’s called a furcula: a little forked structure that’s carried folded up under the body and retained in that position by a tiny hook. The furcula is under tension, like a spring, so when it is released, it flips backward with some force and great speed, and so propels the animal into the air. It’s probably a means of escaping would-be predators.
Springtails are sometimes classified as proper insects and sometimes in a group of their own. However they may be classified, they are a very old group. A fossil springtail is known from rocks over four hundred million years old, and it’s one of the earliest known arthropods (the joint-legged animals such as insects, crabs and shrimp).
All springtails are small. The largest is only ten millimeters long, and most are less than five or six millimeters; some are smaller than one millimeter. But small does not mean insignificant. Springtails are important decomposers and nutrient cyclers; they eat fungal filaments and spores, algae and lichens, organic detritus and some are tiny predators. They also can disperse spores of mycorrhizal fungi that form helpful mutualistic relationships with many plants, carrying these useful fungi to new hosts. A very few are agricultural pests.
Springtails are among the most abundant multicellular creatures on earth. There can be thousands in a shovelful of dirt and leaf litter. They live everywhere: in soil, on tree bark, on leaves in the tree canopy, in caves, in ant nests, in moss and even on the surface of still waters. They’re in Antarctica and the high Arctic, and everywhere in between.
I got my introduction to springtails a very long time ago (perhaps not quite 400 million years, though), as an undergraduate. My major professor was a famous springtail enthusiast, and my job was to crawl around in limestone caves, collecting springtails. I was also supposed to try to rear some of them in the lab, but I think I might have been better at the crawling part, although that got rather spooky at times (but that’s another story…).
In any case, I quickly learned to like these tiny critters. Not only are they generally useful and ecologically important, some of them are downright cute. And some have quite fancy courtship rituals, especially astonishing in a tiny beast with hardly any brain! One species indulges in head-butting bouts between male and female, followed by a whirling dance, and if the male is accepted by the female, he lays down a packet of sperm for her to pick up. You can even see this on YouTube!
Don’t write them off just because they are so small!
• Mary F. Willson is a retired professor of ecology.