Saturday, November 9, 2013

As promised -- a large winter stonefly (genus Taeniopteryx) and possibly a new common stonefly, Agnetina flavescens

This morning I went to the Rivanna River at Darden Towe Park where I did, indeed, find a large winter stonefly -- and possibly something much more exciting.  But more on that later.  One disappointment today: every insect I found was covered with silt.  They were in leaf packs, and the leaf packs were muddy, so the photos are somewhat disappointing.

This is the first genus of large winter that we find in our streams every year -- Taeniopteryx -- and the species is either Taeniopteryx burksi or maura.   The two species can be distinguished when they're adults but not when they're nymphs.

I noted the distinguishing features of Taeniopteryx nymphs in my posting of 10/29 -- all of which are easy to see: the "freckles," the thick based antennae, and the transverse stripe that runs from head to tail.   There's another thing that's easy to see on this nymph that is often true of small Taeniopteryx nymphs: the eyes appear to be red.  And here are the coxal gills, all 6, one at the base of each of the legs.

They sure look like bean sprouts to me!  In any event, we're off on running on large winter season.

And now for our "mystery" bug.

When I took these photos, I was sure that this was the common stone (Perlid) Acroneuria abnormis, so I didn't preserve it.  It was not until I uploaded my photos at home that I noticed two problems:
1) this nymph has a setal row on its occipital ridge,

and 2) it has anal gills.

That makes it genus Agnetina -- not Acroneuria -- Acroneuria nymphs have neither of those morphological features.  At the moment, that's as far as I want to go.  But this could be A. flavescens.  If I decide that's correct, I'll do a separate posting.  But I can't see how it could possibly be the other choices -- A. annulipes or A. capitata.

And speaking of A. annulipes, you may recall that I find them in the Rivanna, and I found a couple today.  Good photos that are spoiled by the silt.

And I found a lot of Giant stoneflies, Pteronarcys dorsata.  This one was fairly mature.  Note the spread of the wing pads.

And I found a very nice small winter stonefly, genus Allocapnia.


More to come on our "mystery" Perlid.  But, we do have large winters at last.

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