Monday, January 30, 2012

New Stream: New Genus of Small Winter Stonefly: Paracapnia

I knew there was something wrong with these wing pads -- so I preserved this nymph for further study.
This one too, a less mature nymph, but one that looked much the same.

Here's the problem -- all of the small winter stoneflies I found in December were genus Allocapnia.  The hind wing pads on Allocapnia nymphs look like this:

They're short and stubby, and the rear edge is essentially flat (truncate).  Now look at the wing pads on the nymph pictured at the top of the page:

Quite different.  The front and rear wing pads are shaped much the same, and the rear edge of the hind wing pads is "rounded"!    So, time to look at Peckarsky (Freshwater Macroinvertebrates, p. 66) where it becomes readily apparent that these are Paracapnia nymphs.  First time I've seen them -- or at least the first time I've identified them.

Peckarsky on Paracapnia: "Numerous conspicuous bristles, mostly along posterior margins of abdominal terga and bordering pronotum and wingpads...head with a dorsal, purple-brown, reticulate pattern [marked by crossing lines], meso- and metathoracic wingpads rounded."

1) I'll let you decide for yourself about the head pattern -- but it looks good to me. 2) We've already seen the rounded wing pads.  3) What about the "hairy" body.  Here's a look at some of the abdominal terga:

That fits.  4) Now what about the pronotum and wing pads?  Are they bordered by bristles?

For sure.  (You can also see the "lines" at the back of the head in this photo.)  So, a new small winter genus -- Paracapnia -- and we can go further.  These are Paracapnia angulata nymphs, since according to Beaty, "Paracapnia angulata is the only species of Paracapnia in the southeastern United States." ("The Plecoptera of North Carolina," p.1)  He also notes that this species is only found in the mountains.

And that's where we were this morning -- back in Sugar Hollow in the Blue Ridge, exploring yet another stream that empties into the Moormans.   It was a beauty.  And now for some more of the beautiful insects we found in this little stream.

1. Another Limnephilid caddsfly larva (Northern Case-maker) -- genus Pycnopsyche -- and again it had made the "three-sided" case out of pieces of leaves.  Interesting point on this type of case: Thomas Ames notes, I noticed last night, that this type of case is typical of early instar larvae.  "Immature larvae that build cases of leaves or other flimsy stuff usually convert them to sturdy rock and twig cases in the final instar." (Caddisflies: A Guide to Eastern Species for Anglers and Other Naturalists, p. 254.)  (For some of the Limnephilid cases that I found last summer, see the entry posted on 9/25.)  This larva made a beautiful case, and in one of the photos, you can see its head right at the edge of the case.

2. A couple of lovely Lepidostomatids.   I actually found quite a few.  Look for them in the leaf packs.

3. A fairly large Ameletid mayfly.  (Lots of them in this stream.)

4. One of many Epeorus pleuralis flatheaded mayflies that was crawling around on the bottoms of rocks.

5. A Peltoperlid (Roach-like stonefly).  These too are common in these small streams in Sugar Hollow.

6. Large winter stonefly: Taenionema atlanticum.

7. And a Chloroperlid (Green) stonefly that had just recently molted.  I couldn't tell what it was until I took a look with the microscope.  But, it was actually the largest Chloroperlid I've seen so far this season. (Genus Sweltsa: note the short tails, the shape of the wing pads, and the very hairy body -- especially the wing pads.)


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