Wednesday, December 11, 2013

Color at last: mature small winter stoneflies, Allocapnia pygmaea

Not exactly the morning I had in mind.  My destination was Buck Mt. Creek, but the water there was high and off-color.  True, we've had a lot of rain in the last 3-4 days -- still I was surprised. But I thought a small stream would be safe and headed to the Whippoorwill Branch of the Mechums.

This is a good stream for Uenoids -- and I found some -- but I saw a lot of small winter stoneflies in the leaf packs that were fairly mature, like the one in the photo above.  Another look.

Like most of the insects we see, the small winter stoneflies don't show off their colors until they reach these final stages.   Based on the work that I've done, I'd conclude that this is Allocapnia pygmaea, a very common small winter species.  For a detailed discussion of the features that lead us to this identification, look back to the posting of 11/4/12.  Here I'll just mention three points.  1) According to Harper & Hynes, A. pygmaea nymphs range from 6 -- 7.5 mm.  This nymph was 6 mm almost exactly.  2) Mature male A. pygmaeas have a long supraanal lobe, around twice the length of tergite 10.  And 3) On mature nymphs there is transverse banding on the abdominal terga.  Features 2 and 3 are both clear in the following photo.

We need the male nymph for exact identification, but I also found a female A. pygmaea today.  Note the difference in the supraanal lobe.  Also, the female abdomen -- and I've observed this before -- seems to be wider than that of the male.

We should see more and more mature small winter stoneflies through December and January and into February as well.

But I was after Uenoids since I've never ID'd those that live in this stream to the level of species. The rocks were covered with Glossosomatids (Saddle case-makers), but I finally found some Uenoids.  I took photos of two, and both were Neophylax oligius, which, says Beaty, is the "most common Neophylax in NC."  (Beaty, "The Trichoptera of North Carolina," p. 87)



The faces give them away -- but let's review Beaty's description.  "N. oligius -- well developed clavate ventral gill on abdominal segment 1; yellow stripe on head, but varies, should be greater than 1/2 head length...underside of head usually testaceous."  (Beaty, p. 87)

The yellow stripes here are clearly greater than 1/2 the length of the head, and the undersides of the heads are indeed "testaceous" (reddish-brown or brownish-yellow).

For the "clavate ventral gills" we need a microscope view.  (clavate = narrow at the base and thick at the top: club-like)


Finally a nice morning after a dark, dreary stretch.  Hope to get out again on Friday.  Might see more of these stoneflies.

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