Another winter wonder: snow fleas springing here and there

Jan was the first to spot the tiny black jumpers, leaping in the snow.

“I’ve got some snow fleas over here,” she shouted to me, about 15 minutes into a mid-February walk through Anchorage’s Ruth Arcand Park.

Jan knows better than anyone my fascination with finding “winter bugs” in our city’s natural areas, a passion I’ve discussed in past City Wilds columns (most recently a December essay, “Snow spiders keep an unusual streak alive”).

Having already found spiders on an early February walk—thus extending my streak of documenting the year-round activity of local “bugs” (which I informally define as insects and arachnids) to 120 consecutive months, now a full decade and counting—I hadn’t been looking closely for the arthropods that wander our forests and meadows even in winter. In fact my mind was wandering in those moments, perhaps thinking about the Super Bowl to be played later that day, when Jan brought it back into a here-and-now focus.

“Snow fleas, wow, that’s great!” I shouted back while bending toward the snowpack for a closer look.

Sure enough, several dark specks not much bigger than grains of ground pepper—small enough to fit on the head of a pin—were scattered on the snow, some of them jumping as snow fleas do when they wish to move quickly from one spot to another.

Now that they were on my radar, I began to see snow fleas everywhere. Temperatures had apparently warmed sufficiently to get them moving and, you might say, springing into action.

It turns out that snow fleas are not fleas at all, but a type of wingless arthropod that’s known, appropriately enough, as springtails. As science writer Ned Rozell has explained, when they feel threatened, “springtails live up to their name by jumping away, using a rigid, forked tail (called a “furcula”) that folds under their body like a jackknife blade. The springtail releases a catch on the underside of the its body when alarmed, and the tail releases, hopefully catapulting the springtail out of harm’s reach.” According to other sources I’ve read, they can leap several inches, though I’ve never witnessed such lengthy jumps.

Here’s something to consider: while I haven’t observed springtails for any substantial length of time, I wonder if they might now and then simply jump for joy and not only out of fear. This may call for additional research.

Springtails are also commonly called snow fleas for a couple of reasons. First, from a distance springtails resemble fleas; and, like fleas, they hop around, though the mechanism of their movement differs. (I’ll also mention here that while fleas have flattened and hard-shelled bodies, springtails have more rounded, softer bodies that are easily crushed. And they don’t bite.) Second, because most springtails are dark in color, they are most easily noticed on the snow, particularly when they cluster in thick masses.

Here’s another thing about snow fleas: scientists don’t consider them “true” insects, apparently because of the way they’re built, though like insects they are “hexapods,” six-legged creatures. Along the forest floor, springtails feed on decaying leaves, wood, and “other organic fare.” They are thus an important component of the forest ecosystem, helping to speed decomposition along.

Like some other small creatures, snow fleas can survive the extreme cold of northern winters because they have an “antifreeze protein,” called glycine, that helps to lower the temperature at which their bodies freeze, allowing them to be active even in below-zero weather.

As we walked through Ruth Arcand Park, Jan and I were greatly impressed by the legions of snow fleas that we saw crawling and springing atop the snow. They seemed to be most abundant in areas thickly populated by spruce trees and we found hardly any while crossing open meadows. This prompted us to wonder if they might drop from trees when the air warms enough.

Most of the information that I’ve been able to track down online indicates that springtails remain active beneath the snow and continue to munch on decaying organic matter even in winter—at least in more moderate climates. However, a colleague of Ned Rozell’s at the University of Alaska Fairbanks, Stephen MacLean, once speculated that they may indeed drop to the ground from trees.

Rozell explained MacLean’s thinking: “Rather than crawling up from the soil, which during the winter would have been snuggly warm under a blanket of snow compared to the frigid air temperature above, MacLean said the springtails may spend the winter clinging to spruce trees.” Then, when temperatures warm sufficiently, “springtails possibly stirred from their winter dormancy and dropped to the snow.”

MacLean further speculated that “Because a springtail doesn’t eat all winter, it might shut down its body processes altogether to save energy. . . . Wintering above the snowpack would keep the springtails’ bodies cold enough to stay dormant until spring weather arrived.”

It should be noted that MacLean presented his “theory” to Rozell back in the mid-1990s, when springtails, by his admission, had largely been overlooked by researchers. It appears that much has been learned since then and the “climb up through the snow” strategy seems to be more widely accepted now, at least based on what I’ve been able to find on the Internet.

For all of that, there seems to be a close association of snow fleas and woodland areas in winter, at least in Ruth Arcand Park.

Whether they climb from below or fall from above, there’s something else I’d like to know: what do snow fleas do when winter temperatures drop again? It would seem a more reasonable strategy to begin tunneling back toward the subnivean zone between snow and ground, where food and warmer temperatures can be found, than to attempt springing onto trees and finding shelter. Perhaps in mid-winter, they simply die in such circumstances. So far I’ve found no answers to such questions, so this is only speculation on my part. It appears I’ll have to do additional digging if I hope to learn more about these tiny winter wonders.

Anchorage nature writer and wildlands/wildlife advocate Bill Sherwonit is a widely published essayist and the author of more than a dozen books, including “Living with Wildness: An Alaskan Odyssey” and “Animal Stories: Encounters with Alaska’s Wildlife.” Readers wishing to send comments or questions directly to Bill may do so at akgriz@hotmail.com