Winter is not generally an ideal time to observe insects in Wisconsin, although I’m seeing a few invasive brown marmorated stink bugs in our house lately. And if you’re thinking that the snow fleas you might see count as insects, think again! As I’ve recently learned, snow fleas are no longer considered insects. Their old insect order, Collembola, was moved into a new class called Entognatha. Collembola, more commonly known as springtails, comprise the largest order in this class.

Why is this interesting? First, it illustrates that we are constantly learning more about the amazing diversity of organisms with which we share the Earth. This reclassification occurred within the past two decades, long after I took entomology in graduate school. But also, Collembola are incredibly interesting and important organisms, and their abundant presence in soil is a good indication of health. Soils that support the prairies, savannas, and gardens at the Arboretum harbor millions of springtails that help with nutrient cycling and soil structure, and they provide a food source for many soil-dwelling predators.

Please bear with me while I share some of what I’ve learned digging into springtail biology over the past few weeks and talking with friends who are equally enamored with cool insects – even when they aren’t really insects! While you may think snow fleas are tiny – they’re about 1.5 mm long – they’re actually pretty big for a springtail. Most springtails are 1 mm (or less) long, about as close as your fingertips could get to each other without actually touching.

The Collembola made their way out of the oceans at least 400 million years ago, well before any insects. With all that time to evolve, they’re among the most numerous of any animal on earth and have been found living over a mile underground in caves and over three miles high on mountain tops. They molt throughout their lives, up to 50 times, and go through breeding and reproductive phases with each molt.

Why aren’t they insects? Like insects, they have bodies with three parts, and six legs. But unlike insects, they have soft bodies, no wings, and simple eyes. Their eyes, for example, are more like the eyes on crustaceans or on immature insects like caterpillars. Their mouthparts are tucked into their heads, not out in the open like insects’ mouthparts. The source of their common name, “springtail,” is an appendage that many Collembola have, a “furca,” which is held under their abdomen and allows them to jump – or spring – away from danger. Given the abundance of springtails, the furcas appear to be quite effective.

Hopefully, your interest in springtails and other tiny organisms is piqued. I love a quote by Paul Harvey, who said “Despite all our accomplishments, we owe our existence to a six-inch layer of topsoil and the fact that it rains.”

It behooves us to learn as much as we can about what is going on in that layer of topsoil. I highly recommend a website called a Chaos of Delight, written by photographer and blogger Andy Murray. His photos of springtails (including the Pantomime springtail pictured above), nematodes, and other soil organisms are amazing.

—Karen Oberhauser, director