Aquatic Insects of Central Virginia: Strophopteryx, Strophopteryx, Strophopteryx! Must be January at Buck Mt. Creek

Sunday, January 1, 2012

Strophopteryx, Strophopteryx, Strophopteryx! Must be January at Buck Mt. Creek

The large winter stonefly, Strophopteryx fasciata -- as in the photo above -- will probably dominate my findings at Buck Mt. Creek for the next month to month and a half. This morning they were all over the place, both on the bottoms of rocks and in the leaf packs. Of the insects I collected to look at -- I found one Helopicus Perlodid stonefly, three or four Clioperla Perlodid stoneflies, two Uenoid case-making caddisflies, one small minnow mayfly (more about that in a moment) -- and twenty to thirty S. fasciata large winter stoneflies. I didn't see a single Taeniopteryx large winter stonefly -- though I'm sure there are still some around.

And I found small nymphs, medium-sized nymphs, and some nymphs -- like the one in the photo above -- that are already pretty darn large. E.g.

Small

Medium

Large (not the same nymph pictured in the photo above)

If you monitor streams and you see nymphs that look like this -- yellow and brown, or yellow and green, with "mottled" head, pronotum and wing pads, and clearly banded abdominal segments -- you've
found large winter stoneflies. But, you want to be careful: keep a few for "certain ID" in your lab. This is the large winter with the "triangular, ventroapical plate," and that's not necessarily something you'll see with your loupe.

And let me remind those who monitor streams that this is one place where Voshell's Guide to Common Freshwater Invertebrates can be misleading. The large winter stonefly that he shows in his book on p. 134 (plate 47) is Taeniopteryx burksi (with coxal gills) -- this one --

and this is not the most common large winter stonefly we find in a lot of our streams in this part of Virginia. Come late December, in the streams that I look at, S. fasciata large winters will out-number T. burksi large winters ten to one (well, I haven't counted -- but you get my point). Voshell's book is so important for those of us learning family ID of these insects that I wish he had said more about this.
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We move on... My big surprise for the day was finding this little nymph.

Yes, indeed -- it's the first small minnow mayfly of the new year and new season. It's great to see them return, and the numbers will increase in this stream and others (the Doyles, Powells Creek, the Lynch River) as we move from January to March. I am quite sure that this is the same species that I saw in these streams in the winter last year, and I'm fairly sure it's Heterocloeon amplum. Note that it has only two tails: that means that the genus is either Acentrella or Heterocloeon (all Baetis nymphs have three tails), and it sure isn't A. nadineae or A. turbida -- it's a Heterocloeon. But let's look at the ID issue in greater detail when we have larger specimens that we can examine. Still, you can probably note the resemblance to this H. amplum nymph that I found in Buck Mt. Creek in March of last year.