Sunday, December 11, 2011

Large Winter Stonefly, Species Number Two: Taenionema atlanticum

I've been kept from the streams all week long by high, fast, muddy water -- the result of 3+ inches of rain on Tuesday and Wednesday.  But my good friend in Sugar Hollow said that her stream -- a small one that flows into the Moormans -- was actually running a little bit low.  So, today it was back to my favorite part of our watershed.

This is a very small stream with a lot of drop in elevation, and it's surrounded by beautiful bolders and rocky outcrops.  I was expecting to see Chloroperlids (Green stoneflies) and Perlodids, but not the insect in the photo above.  This is a small, large winter stonefly, Taenionema atlanticum (atlanticum is the only species of Taenionema on the East coast), a species that Beaty notes is a mountain nymph that is "rarely collected" ("The Plecoptera of North Carolina," p. 7).  Still, I found one last year in this very same stream, and reported that find on March 17th.  This is one of the photos I took that day.

You may recall that Taenionema large winter nymphs resemble Strophopteryx large winter nymphs (Strophopteryx nymphs will show up any day now) in having a "triangular, ventroapical plate."  This:

But there are a number of ways to distinguish these two genera, one of them being the shape of that plate when viewed from the front.  Let me quote the description from Stewart and Stark (Nymphs of North American Stonefly Genera, p. 241): "Male abdominal sternum produced into a plate, broadly triangular in posterior half and bearing short erect hairs in posterior two-thirds.  Female 9th sternum similar to that of male except much more rounded apically."  From this microscope photo, and from the plates in Stewart and Stark (p. 240) I'd conclude that the one that I found this morning was a male.

The Strophopteryx ventroapical plate, by way of contrast, is "tubular" in shape as it narrows down to the end.  This is the photo I posted last year.  (See Stewart and Stark, p. 237, for illustrations.)

For more on the distinction between these two genera, you might want to look back to the posting of March 24th.  In the meantime, here are two more views of this morning's find.  Taenionema atlanticum.

But I found another nymph this morning that was also unexpected: a spiny crawler mayfly (Ephemerellidae), genus Eurylophella.  This is the spiny crawler with "operculate gills," large gill plates on segments 4 and 5 that cover those on 6 and 7.

I found one of these last spring in Sugar Hollow on March 22nd, and a mature one in Buck Mt. Creek on June 3rd.  But it's December (!), so I'm not sure why this genus is in here this early.  This is something I'll have to look into.

And I have other things that I need to study.  I found a flatheaded mayfly this morning -- Maccaffertium -- that was very unique (color and pattern), and I'd like to see if I can nail down the species.  And, I found a small free-living caddisfly larva -- not R. fuscula, the green one -- that I'd also like to get down to species ID.  Pictures.

So, work to do for the next rainy day!

Oh, and there were Chloroperlids, lots of them in fact, but very small and light in color.

No small winter stoneflies in this little stream.  But I did find some in a small stream on the other side of the valley, along with another Leuctrid nymph (Rolled-winged stonefly).

The dominant taxon today?  Roach-like stonefly, just as it was one week ago on the other side of the valley.

Below: the tiny, but very good,  stream in Sugar Hollow that I went to this morning.

No comments:

Post a Comment