Friday, November 15, 2013

Small and large winter stoneflies at Buck Mt. Creek -- and a beautiful common stone, Acroneuria carolinensis

With the clouds moving in for several days, I thought I'd see what I could find at Buck Mt. Creek.  And, at last, I found a fair number of small and large winter stoneflies.  But could I not, not begin with these photos?

The common stonefly, Acroneuria carolinensis.

The key to distinguishing A. carolinesis from the more commonly seen A. abnormis is the abdominal banding.   On A. abnormis nymphs the anterior margins of each of the terga are dark while the posterior margins are light: the banding is reversed on A. carolinensis.  Those bands are fairly easy to see on both of the photos above.

Although this isn't mentioned in any key that I've seen, there seems to be one other way to distinguish these species.  The femora on A. abnormis are uniform in color (gray/brown) without any banding; those of A. carolinesis are light in the middle with dark bands on both of the ends.

A. abnormis:

A. carolinensis

In any event, it was a beautiful stonefly -- and the lighting was good for some photos.

Small winter stoneflies.  I finally saw them in significant numbers, crawling on leaves in the leafpacks.  You have to be alert for any movement, they really are small stoneflies -- these were ~ 6 mm --and fairly light in color!  But, here's a nice pair.

Beaty cautions to leave the small winter ID at the level of genus -- these are both Allocapnia nymphs -- and as I found out last year, species ID is not at all easy.  Still, last year I felt that I could distinguish two Allocapnia species, A. pygmaea and A. mystica, and I think that's what we have here (pygmaea on the left, mystica on the right).   To see the case that I made, please look back to the posting of 11/4/12.  Clearly A. pymaea is a larger nymph -- with a larger head and larger wing pads -- and note that the pronotums of the two species are not shaped the same.

A. pygmaea (I think)

and A. mystica

I'll review these ID's when I find small winter nymphs that are mature.

Large winter stoneflies.  And I found a fair number of large winters as well, genus Taeniopteryx. Did I mention that the eyes often look red?!


But this A. carolinensis was surely the find of the day.

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