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The migratory habits of the humble Wisconsin snow flea: now there's something to study on an uninspired winter's day.
Scholarly papers have been published on the timed travels of Norwegian snow fleas, but you don't have to be a Ph.D. or live near Oslo to take up this hobby. Snow fleas are very likely cavorting around in your back yard right now.
These sturdy, wingless fleas, known popularly as springtails and technically (in Wisconsin) as Hypogastrura nivicola, are members of a group of acrobatic arthropods called Collembola (kol-LEM-bo-la). Don't start itching, the three-millimeter (about 1/8-inch long) creatures prefer leaf mold and fungi to blood. In the winter, when warm sun heats up the air, springtails often climb through snow layers to congregate on bare spots at the bases of trees or on the snow itself. Most insects find cold weather and snow rather unappealing, but snow fleas – which are neither true fleas, nor true insects – actually thrive in it.
Just imagine their undercover lives this way, as does Kenneth Christiansen, emeritus professor of biology at Iowa's Grinnell College: "They're semi-comatose – and then all of a sudden it's like Times Square. They come to life, and start pushing each other away – like they're trying to escape the mob." In Norway on mild winter days, wholesale emigration of snow flea populations serves two purposes: to find new places to reproduce and to mix the gene pool.
Christiansen co-authored two tomes on springtails, The Collembola of North America North of the Rio Grande and The Collembola of Hawaii, as well as many journal articles. He's stalked them in caves, housed them in jars, and occasionally flushed them down the drain (on a "voyage of exploration," Christiansen calls it) when their fecundity became overwhelming. It's a good thing there are no Collembola animal rights activists, he adds, or he'd be in trouble.
Springtails' reputation for acrobatics, and thus their association with nature's most annoying gymnasts – common dog fleas – derives from their ability to vault great distances. A cocked spring on their abdomens, called a furcula, snaps suddenly when released, propelling the animal into the air. Springing can be a superb way to evade predators, such as mites and beetles, but it does have one drawback: Collembola can't control their direction and frequently land in the same spot they jumped from.
Being all but brainless has its advantages, Christiansen says with a chuckle. "We think they're probably relatively free from psychological stress."
Collembola date back to well before dinosaurs, to the middle Paleozoic era, about 400 million years ago. Lungfish, those famous "living fossils" that still survive in warm spots today, were just beginning to gulp air at the brims of stagnant pools. During that time, the land began gradually to carry a patina of the first true plants. Their remains were discovered as fossilized nuclei in the late 1800s in a glassy rock called chert, near the town of Rhynie in Scotland. The chert had hardened from marshy soils at the edge of a small lake, and with those first mysterious plant fossils was found the remains of a tiny animal – the snow flea.
Scientists immediately appreciated their new find. The creature possessed six abdominal segments rather than the eleven of true insects, no wings, and an appendage poking down from the first segment that seemingly held the creature fast to a surface. That appendage, in fact, is how Collembola were named, combining the Greek words "coll," or glue, and "embol," meaning a wedge.
Their ability to adhere to the underside of a leaf may have its merits, but the sticky extra limb, called a ventral tube, is also used for drinking and breathing. Scientists are still determining whether the tube is also used for excretion.
Back in the 1800s, scientists naturally classified the newly found creature in the phylum Arthropoda, a huge group of creatures with external skeletons and jointed bodies, that encompasses three-fourths of all known animals.
Deciding exactly where to place Collembola within a group that includes butterflies, prawns, and spiders gets tough. Do Collembola belong in the massive class Insecta, or should we consider them insects at all? Some scientists think they resemble crustaceans more closely. Or perhaps they deserve their own class entirely, as most believe, in appreciation of certain differences in anatomy and genetics.
Among biologists, there is ongoing debate between taxonomists who prefer more categories (the splitters) and field ecologists who desire fewer (the lumpers). Christiansen thinks of himself as a lumper but says he hasn't got time to quibble. "They're small arthropods related to insects," he declares. End of discussion.
Since the day Collembola were first discovered, thousands of species displaying attractive hues have been found living in almost every strata of society. For the most part they are harmless, help to break down dead plants, and control bacteria and fungi, although one species (Sminthurus viridis) found in New Zealand and Australia likes to eat alfalfa.
Colembolla generally prefer moist, cool conditions, which explains why the genus Anurida lives in intertidal pools, how Folsomia candida came to be under your flowerpots, and how one researcher collecting a species in Alaska found Collembola on a handkerchief after he sneezed!
That occurred because the time-honored way to gather such tiny animals is by sucking them up through an aspirator: a stoppered bottle with two tubes sticking out, one for drawing in a breath to create a vacuum and the other for sucking the Collembola into the jar. You get the general idea.
"Let's put it this way," said the good professor. "It's not a major health concern for everyone."
Christiansen never suffered the same fate, though he has collected Collembola using the same technique all over the world and quite frequently in Wisconsin. In the 1950s, he found snow fleas under bark and in leaf mold in Sawyer County, on dung in a cave in Pierce County and on the surface of water in a Richland County cave. Another scientist found the first known location of one species, Onychiurus talus, in Devil's Lake State Park in 1950.
Another springtail species is especially friendly. Perhaps you've seen this black-colored species dashing across the page of a book or a letter you were penning. Next time you see such an "animated comma," as Christiansen calls them, say hello to Willowsia nigromaculata.
Collembola have distinguished themselves as some of the hardiest animals ever. Over 6,000 species have been described, and their evolutionary longevity can be attributed to several factors, Christiansen says. They eat just about anything, including their own droppings, or nothing at all. Christiansen has deprived Collembola of food for up to four years in his laboratory. Folsomia candida actually thrived when fed DDT. It was hoped these creatures could be used in decontamination work. Then researchers discovered the Collembola were transforming DDT into DDE, which is almost as toxic.
Collembola also can endure hot temperatures as well as cold, with species found in Hawaiian volcanoes as well as in the Antarctic.
In a sense, it's reassuring to know that in this age of concern for biodiversity, there are creatures so adaptable that almost nothing we do bothers them. That makes them almost perfect pets, according to those who have stored springtails for months in margarine containers with see-through lids, adding a little yeast for food every so often.
Snow fleas don't bark. They don't whine. They don't choke on hairballs, nor slop water all over the kitchen floor, nor leave tufts of fur on the living room couch. Finding a few to start your collection could be as easy as turning over a rock in the woods or inspecting the ground under trees.
And, should you reach that day when you find that indoor flea watching has its limits, you can pry open the lid and send your new friends on a voyage of exploration to a snowbank outdoors. They may not be as adventurous as their Norwegian counterparts, but at least you won't have the fate of snow fleas on your conscience...they'll make it.
Katherine Esposito is staff writer for Wisconsin Natural Resources in Madison.