Winter stoneflies do not seem to care that the river in front of our house is narrow enough to be designated as a “no wake zone” for motorboats. After the ice has gone out in February, the winter stoneflies disregard that designation, and they go waterskiing. They brazenly waterski right up to the rocks of our riverbank.
Actually, you might describe them differently if you would happen to stop in for a visit on the right February day at our riverside home, and we went out to watch those water-skiing stoneflies. You might describe them as skimming across the water surface like an airboat instead of waterskiing. I guess I call it waterskiing because it reminds me of the barefoot waterskiing I saw once.
In a somewhat similar manner, the winter stoneflies will walk around on the water for awhile after they emerge, then raise themselves up on all six legs (some species do 4- or 2-leg skiing) and flap their wings. This propels them across the water almost like a barefoot skier. And since you stopped in and are standing here with me watching the stoneflies waterski, don’t you agree that they do make quite an interesting wake?
Anyway, back to the rocks. We watch as the stoneflies ski to the rocks, scramble up the riverbank, and scurry across the snow-covered yard. We marvel at their ability to withstand the cold. Winter stoneflies have some pretty good natural antifreeze. For some reason, the stoneflies like to gather on our screened-in porch, and they appear to be looking forlornly in at our cozy wood stove. With stoneflies all over our window screens, window frames, and even the brick chimney, perhaps you are thinking, I’m glad I don’t live beside a river. Well, after we take a look at what is really going on—we’ll get to their drum fest shortly—and see the stoneflies’ former life, maybe you will change your mind.
Let me fetch my water-world viewer and we’ll look at the leaf-pack habitat of the stonefly nymphs. I like to use a glass aquarium with the four sides painted black to investigate the underwater world. I simply set it on the water’s surface, and we can look down into the water without the glare of the water surface. Snorkeling would give a better view—but brrrr—so we’ll settle for the aquarium window.
We can see clumps of leaves caught against rocks and sticks. These leaves fell into the river last fall and have been colonized by bacteria, algae, and protozoa.(What a zoo to explore if you have a microscope!) The stoneflies we see emerging from the river have spent their lives so far as nymphs feeding on those fallen, enriched leaves and/or aquatic vegetation.
We observe some winter stonefly nymphs as they wiggle their way to the surface and climb out onto the rocks. We even get to witness one shedding its skin as it emerges into an adult stonefly. The nymphs’ shucks, or exuvia, are scattered over the rocks and streamside vegetation.
I should mention that the waterskiing stoneflies we saw are species of the genus Taeniopteryx. There are other species of winter-emerging stoneflies. We see smaller stoneflies crossing the snow to the porch. These are the Small Winter stoneflies (family: Capniidae).
Take note how happy the Mallards are with the winter stonefly hatch. They gave up dabbling for food over against the far shore and took to drift feeding just upstream from where we are watching the stoneflies. They drift feed by paddling against the current to stay in place so they can snatch up their food as it comes to meet them in the current.
The glossary of Aquatic Entomology by W. P. McCafferty defines “drift” as, “Benthic organisms during the time they passively move downstream in a suspended manner; to be temporarily suspended and carried by the current.” So, in our instance, drift is stonefly nymphs rising through the water column from their former home on the river bottom to their new one—perhaps our porch; perhaps a duck belly.
When our stoneflies emerged from the water, shed their last nymph-stage skin, became winged adults, and scrambled across the snowy yard to our porch (or the riverside vegetation), they joined in a drumming festival. Now, we can’t hear anything, because theirs is an inaudible drum fest. They just look like they are sitting there staring in at our wood stove, but they are actually drumming out code with their abdomens. This code drumming is technically called “tremulation.” Or, if you like using lots of big words, you might refer to the drumming as “substrate-borne bioacoustic communication.”
Of course, the stoneflies, if they are on the same continuous substrate, can hear the other stoneflies’ code-talk even if we can’t. This is how they find each other. As you sit by your fire reading this, I might be at my home by the river, actually listening to them. This year I hope to use a microphone/amplification system so I can hear their drum fest. After all, rigging up a system like that would be useful to hear other critters that use substrate-borne bioacoustic communication. Wouldn’t that be fun?
Soon there will be stonefly eggs laid in the river. Shortly after that the eggs will hatch and the nymphs will feed and grow until the summer’s warm waters cause them to become inactive, somewhat like hibernation. At least that’s how it is for some species of winter stonefly nymphs. Think about it. While all the buzzing and singing and summer bug drum fests are happening, winter stonefly nymphs are…sleeping. What a strange life! Why? Why such a seemingly backwards life?
Hey, look at that! A bluebird is sitting on our wash-line post. Don’t you pity it? It’s just sitting there vainly surveying the snow-covered yard for some food. What was it thinking that it stayed here in northern Pennsylvania during the winter? I’m sure it is tired of eating winterberries, as they seem to be simply for emergency rations. Oh, the bluebird just swooped down onto the snow to snatch up some kind of prey! Now, just what kind of insect could possibly be running around on the snow in February?
I think you’ll “get my drift,” at least if you read last month’s article about God’s bird feeders. Have you noticed any other ways God feeds the birds?
