Tuesday, December 3, 2013
The "other" small winter stonefly that we see in at least one of our streams: Paracapnia angulata
No, no -- that's not a small winter stonefly, but it's a nice photo to start off this entry. The Perlodid stonefly Malirekus hastatus for which see the entry of 1/29/12 (full discussion of the ID). The backs of the wing pads reveal that this nymph still has a long way to go before becoming mature (it was only 11 mm), but it lacks nothing in color and pattern. Got some nice photos.
Now on to the big story. As you know, almost all of the small winter stoneflies we see in our streams are genus Allocapnia, mostly, I think, A. pygmaea and A. mystica. They're common at this time of year, with a genus tolerance value of 3.3. But I had found some "non" Allocapnia Capniids, Paracapnia angulata, in a small headwater stream in Sugar Hollow back in January, 2012. Today my friend and I went back to that stream, and sure enough we found them again!
Yes I know, they're not much to look at: they were only 5 mm. But they're real beauties when they mature. Below, the two that I found on 1/30/12.
Since I just discussed how Paracapnia differ from Allocapnia nymphs (11/22/13), I won't belabor the point. But the key thing is the shape of the wing pads: "meso- and metathoracic wing pads rounded" (Peckarsky, Freshwater Macroinvertebrates, p. 66). I.e.
The wing pads are real hard to see on the nymphs that I found since they're so small -- but you can see them in these microscope views.
The "hairy" body -- clearly visible in these microscope photos -- is characteristic of the species (Stewart and Stark, pp. 141-144). So too, I take it, is the oddly shaped abdomen -- bulbous? -- which swells dramatically from front to back on very young nymphs (see Donald Chandler's photo at http://www.discoverlife.org/mp/20q?search=Paracapnia+angulata).
Very cool. This is one of the things I was hoping that we'd see today. It's so nice when you find what you're after. North carolina, by the way, does not assign a tolerance value to P. angulata. That means they have not found enough samples. Beaty does comment however: "Nymphs are collected late fall through mid-winter in the Mountains only," and "Nymphs typically occur in small headwater streams, possibly in leaf packs." (Beaty, "The Plecoptera of North Carolina," p. 1) That's where they were: I found them in leaf packs in a small headwater stream in the mountains (elevation, ~1200 FASL).
We saw a lot of Peltoperlids (Roach-like stoneflies) today and a lot of common stoneflies -- Eccoptura xanthenses -- both of which are common in these small headwater streams. And we found some flatheaded mayflies, M. merririvulanum and M. pudicum. But I only photographed two other insects.
1. A Leuctrid -- rolled-winged stonefly -- the first I've seen so far this year, and I saw more than one. Notice the long, thin abdomen.
2. And a spectacular Ameletid mayfly -- probably Ameletus cryptostimulus, but it's a little too early to call that for sure.
Oh. I did find an Allocapnia small winter stonefly as well. So they are found together. Think this one is A. mystica.