Snow Hikes, Snow Spiders, Snow Flies, Oh My!

By Cassie Sevigny

Bear Creek (Photo by Cassie Sevigny)

I went hiking this weekend with a friend who's moving away from Montana. We drove up to Bear Creek trail, expecting mud and a trail-turned-creek, but spring is not so progressed yet. Instead we found a low-traffic, barely-compressed solid snow trail that was much easier to traverse. The snow lay in heaps on rocks like pillows, hid the true edges of the creek, stuck in frozen puffs to the sides of small trees, and reflected the days brilliant cold sunshine back at us. Good thing I wore sunscreen!

As we walked I noticed little black spiders on the trail. Warming up, perhaps? Despite their dark color against the white, they blended in with all the other natural debris flecking the snow. Only their flicking legs caught my attention. I wondered if these spiders just didn't go dormant for winter, or if the sun was waking them up.

Snow pillows (Photo by Cassie Sevigny)

Then in an open snowfield I saw another bug crawling - black and winged, crawling uphill away from the creek. Two tails, wings folded neatly over each other on its back, made me guess it could be a stonefly. One fly is just a curiosity, until my friend said he's seen some earlier. And then there was another. And two more. All crawling uphill, crossing the trail a decent ways away from the creek. Perhaps a hatch? Were these the very winter stoneflies WEN featured on Science Friday?

Winter stoneflies are not very strong fliers and instead walk around on the ice and snow looking for a mate, just like the ones I saw. Their dark color may help them better absorb the heat from the sun when emerging in such cold months, though they also have their own internal antifreeze! 

Snow fly (Photo by Cassie Sevigny)

I was probably seeing the aptly named "small winter stonefly" (capniidae) since these were smaller and more delicate than most stoneflies I have seen around the Clark Fork in the summer. Missoulian Angler confirms that small winter stoneflies emerge in February and March, and have been found around the Bitterroot River, of which Bear Creek is a tributary. Missoulian Angler also informs me that they have a much cooler name, the "snow fly," which I shall use from now on!

I saw more and more spiders as we hiked too, now that I was looking for any black moving speck in our path. Were the spiders emerging too? Were they looking to eat the stoneflies? My search for information pulled up another blog where someone else wondered the same thing, but for streamside spiders catching insects in their webs. I only saw the spiders. I forgot to photograph the spiders I saw so I cannot identify them precisely, but they were small and black, like many of the spiders active during winter. (Most spiders go dormant to survive the cold.) Maybe they are black for the same reason as their potential prey - to stay warm.

While I found no definitive answer to whether the black snow spiders eat the black snow flies, I was delighted I could reasonably speculate! Working with WEN enabled me to guess that I was seeing some kind of stonefly, and also exposed me to the theoretical existence of winter stoneflies. Finding them in the wild and relating them to the environment I found them in made the cool science facts so much more real, tangible, and relevant to me. Finding small details in a landscape and being able to understand them, or hazard a guess as to their role, also enhances my experience outdoors and makes me feel more connected to the environment than if I saw hikes as "just passing through." Chance encounters with tiny wildlife can mean just as much as the sun shining beautifully between the tall thin  evergreens or the companion you talk to on the way, and I'm glad I had all three.

Photo by Cassie Sevigny