Winter Stoneflies

2008 April 26

April 4 was pretty warm[1], so we went down to the Pilgrim River just east of Houghton to see if the walking trails beside the river had melted off enough to be passible[2]. While we were there, we noticed that there were small, black insects hanging out on the wooden bridge railings

largestoneflyrailing.jpg

smallstoneflyrailing.jpg

So we captured several of them in jars and brought them home where we could take better pictures[3][4]. We had two distinct types of specimens: a larger one that had full-sized, functional wings:

largestoneflysideview.jpg

and smaller ones with stubby wings that looked totally inadequate for flight:

april-6-larger-stonefly-dorsal.jpg

april-6-small-stonefly-dorsal.jpg

These are Winter Stoneflies, order Plecoptera[6], family Taeniopterygidae. This is yet another order of insects where the nymphs are fully aquatic, while the adults are a terrestrial form and usually have wings. Stoneflies in general may transform to adults at pretty much any time of year, but the winter stoneflies specifically come out as soon as the rivers open up, and mate/lay eggs before most of the predators either emerge from whatever form that the overwintered as, or migrate back into the area. They have a habit of sunning themselves on railings, trees, and rocks near streams, warming up enough that they can seek out mates and (if winged) fly off and disperse to lay eggs. I expect that the winter stoneflies are jet-black specifically so that they can absorb heat from the sun as quickly as possible. The nymphs are “shredders”, eating bits of decaying plant matter in the water, pretty much like the caddisflies and the amphipods from the last two weeks. There seems to be a lot of that going around, probably because in streams, bits of decaying plant matter are the most common food source and so anything that eats it can become very plentiful.

I’m pretty sure that the specimens I have pictures of here are at least two species (one flying, one non-flying), maybe three (the two with non-functional wings have different body/wing length ratios, but this could either be because they are different species, or because this is the normal range of variation for one species. Maybe one is male and the other female). There is probably a bit of advantage for the non-flying forms, they seemed more active and more numerous than the winged form. Insects evidently have to warm up their flight muscles to quite a high temperature before they can fly, so forms that spend a lot of time in cold conditions probably don’t get a lot of benefit from the wings. The non-flying forms can therefore spend a lot more time mating and laying eggs, and less time sitting around sunning themselves to get warm enough to make their wings work.

————
[1] That didn’t last. Less than a week later, we got a blizzard that dumped about a foot of snow on us. Will winter never end?

[2] It hadn’t. The boardwalks still had over a foot of kind of slushy snow on them, so we just went down to the pedestrial/bicycle/snowmobile bridge to watch the water rush underneath.

[3] OK, this is another set that bends the rules a bit. They weren’t captured on the property, but I would not be at all surprised to find them here, since they could easily live in the same little stream that the gammarus and the caddisflies live in.

[4] All of these were really hard to photograph, because they have the standard problem of all the cold-tolerant species: once they get into a warm house, they overheat and go into a sort of frantic overdrive mode where they scurry, scurry, scurry and refuse to sit still for anything. For the large winged one, I ultimately ended up putting some snow with it in the petri dish and putting a glass cover slip over it to keep it from escaping. For the smaller ones, I made an insert out of plastic[5] to hold the cover slip in place and sealed, and then refrigerated the whole works so that they’d be properly cooled.

[5] The problem I’ve been having is that the cover slip I have isn’t quite as wide as the petri dish, so it leaves a gap on one side that scurrying critters insist on crawling through. Putting snow in the dish made it possible to mound up material on one side to close off the gap, which helped a lot for keeping the stonefly from escaping. So, I made a plastic insert out of Shapelock, a special plastic that softens in hot water so that it can be molded like modeling clay until it cools off. Once it cools, it gets pretty rigid and looks and feels like high-density polyethylene. It’s great stuff, I bought a pound of it a while back and have used it for all sorts of fiddly little things where I needed to make a strong small part quickly. A pound goes quite a long way, too, I’ve still got over 3/4 of the container left. So now, I can not only put the glass cover on the petri dish without leaving a gap, but the plastic also has a lot of heat capacity, so if it is chilled in the refrigerator it works to keep these cold-tolerant insects cool enough that they slow down and act normal. I wish now I’d done this for the snow fly a while back.

[6] In the last three postings, I just added three arthropod orders (amphipodia, trichoptera, and plecoptera), increasing the number of orders that I have entries for by over 20%. All because of grabbing specimens from streams, an environment that I hadn’t been photographing much before now.

4 Responses leave one →
  1. April 27, 2008

    Insects evidently have to warm up their flight muscles to quite a high temperature before they can fly

    I’ve wondered about this, particularly when talking about bees and wasps. Is there something particular to the flight muscles that requires high temperatures? Or is it the insect metabolism in general? The scurrying you mention about (when bringing insects into your house) seems to indicate the latter. But I thought I’ve read that bees also vibrate their wings before take-off, in order to warm up that part of their body.

    I wish I could give myself more energy just by cranking up the thermostat.

  2. April 27, 2008

    …and I just placed an order for some Shapelock. That stuff looks pretty cool.

  3. April 27, 2008

    I’m not sure if they run around like that in a warm room because they are more alert and energetic when they warm up, or if it’s more along the lines of “AAAAHHHHHH! I’m on fire! I’m burning up! AAAAAHHHH! Put it out!”. From their behavior, I’m afraid it’s probably the second reaction.

    This paper is a bit technical, but reading through it, it sounds like there are two issues with insects flying at low temperatures: (1) the temperature where the muscles can begin to “shiver”; and (2) the temperature where the muscles can produce enough power to fly. Cold muscles can do low-power things like moving the legs around slowly, but they can’t “buzz” the wings for flight, and if they are too cold, they can’t even shiver. Once the insect is warm enough to start shivering, it can warm up the wing muscles enough to get them to a temperature where they can produce enough power to fly. There’s evidently a lot of variation in the minimum shivering temperature – honeybees lose the ability to shiver and lapse into a coma at around 10 degrees C (about 50 F), while certain cold-adapted moths can shiver all the way down to the freezing point.

  4. June 23, 2012

    A praovoctive insight! Just what we need!

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