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Desperately seeking snow fleas with melting snow

February 26, 2014

As the temperatures crept above freezing and the thaw took hold, the hard edge of February turned soft and snow-generated fog settled over the ridge.

When the temperature topped 50 on Saturday and I’d finished running the myriad of errands that kept me from doing what really needed to be done—to wit, checking up on the natural world—I grabbed my camera and a magnifying glass and headed out into the woods. I was on a mission: a find-the-snow-fleas mission.

Now, long-time readers of this Journal have often heard, probably too-often, I’d reckon, the infamous tale of how these minuscule arachnids tricked the Naturalist into predicting an early spring. Without going into detail, suffice it to say the column in question, the second one I’d ever written, appeared in print in the issue of this newspaper that was devoted to coverage of the paralyzing Blizzard of ’78, the storm by which every nor’easter before and since has been, is, and will be measured. I was so embarrassed by this gaffe that I very nearly buried my head in a 10-foot-deep snow bank and gave up writing forever.

However, while, for better or worse, I decided to soldier on in the scrivening trade, I’ve definitely left forecasting to groundhogs and Weather Channel sages. That said, when the conditions are right, I continue to seek out snow fleas, not as prognosticators of a change in the weather but rather as curiosities that speak volumes about current conditions.

The conditions were right last weekend, and in the soft, melting snow, I peered around the newly exposed bases of tree after tree. My quarry: a collection of pepper grains on the snow… pepper grains that hopped.

Almost half-a-century ago, when I was trying—in vain, it turned out (that’s a story for another time)—to become a genuine biologist, snow fleas were considered to be genuine insects and assigned to the insect order Collembola. These critters, many of which are no bigger than the head of a pin, are oddballs, since they lack very compound eyes and their body plans and behaviors don’t quite fit the standard insect model. So, in the years since I first memorized my insect classification schemes, taxonomists decided that collembolans weren’t, in fact, insects at all. They were certainly close cousins, but their fundamental differences merited separation and the creation of a new arthropod hierarchy. All of the six-legged critters were placed under a taxonomic umbrella called the Class Hexapoda, and it included both the Order Insecta and the Order Collembola.

This required some relearning and some changes, but hey, even at my advanced age, relearning and change are good things. Honest.

Wherever you place snow fleas in the classification world, they’re fascinating insects—whoops, hexapods… old habits die hard—because of two traits. The first is their means of getting from place to place. Collembolans have six proper legs, of course, but at their hind end is an inventive double-tail-like device called a furcula that can be snapped under the abdomen into a catch known as the tenaculum. When the furcula is released, the critter springs forward rapidly, as much as 50 body-lengths at a clip. This ability gives it the name “springtail”—real fleas use their hind legs as springs—so both kinds of arthropods hop, but via different mechanisms.

The second intriguing aspect of the collembolan lifestyle is what brought me outside in the first place: the “snow” part of their common name. Snow fleas are endowed with a remarkable protein antifreeze that enables them to move about in the cold. Normally, the collembola, which are among the premier decomposers of the invertebrate world, are content to spend their obscure days breaking down leaf litter and fungi. But if the soil gets saturated with water, as it does when the snow starts to melt quickly, the snow fleas will, to avoid drowning, navigate upward to the snow surface. There, these hopping grains of pepper may engage the attention of cross-country skiers, snow-shoers, and naturalists, and it was in this hope that I searched and searched for them throughout the weekend..

I searched, alas, in vain.

I’m not sure why the collembolans weren’t out and about, for many of the other early-appearing signs of winter’s approaching end were on display. No sooner had the sudden warmth brought in an unexpected thunderstorm and turned the snow to fog than the bridge railings were highways for stone flies. The more exposed areas of the woods were now dotted with rocks, logs, and clumps of mosses, newly emerged from their white blankets. The local streams, fueled by snowmelt and taking a cue from the thunder, found their voices and started to roar once again. A young downy woodpecker, its brain perhaps addled by an early rush of mating hormones, thudded into our kitchen window then sat on the ground, dazed and trying to get its bearings again. I guarded the bird until it was able to fly, first to a picnic table bench and finally to safety in a tree. I think it came through the collision in fine shape.

Finally, there was the first sighting of the skunk cabbage, a sure sign that I should be seeing snow fleas. Lots of plants get through winter by playing a waiting game, but Symplocarpus foetidus has evolved the rare ability to turn the tables on the cold. The impatient species makes its own heat and ends winter early. It may be below freezing outdoors, maybe even well below freezing, but in the dark-colored “hot houses” that shelter the skunk cabbage flowers, the temperature’s in the 70s—and the plant has a thermostat that keeps the warmth relatively constant.

The well-insulated and efficient furnace, coupled with the flower hood’s ability to harvest and store solar energy, means that a skunk cabbage can often melt its way out of the snow pack. Pollinating insects, typically cold-resistant flies and the earliest of bees, are attracted to the warmth, as well as to the mephitic odor. From the set of tracks in the vicinity of the skunk cabbage plants, and from the damage the flowers incurred, it appears that a group of wild turkeys found this source of unexpected fresh greenery irresistible, too.

But the snow fleas, well, they didn’t follow the snowmelt above-ground. Maybe they were taking the prediction of a certain Pennsylvania rodent to heart. Maybe they were tuned into the Weather Channel. Whatever the reason for their reticence, the collembolans stayed in the safety of the leaf litter. They weren’t fooled by the brief thaw. They somehow knew that winter was planning a return. They weren’t wrong.


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