Friday, October 5, 2012

Acentrella Turbida: A Small One to Start off the Season

The small minnow mayfly, Acentrella turbida, is "bi-brooded," hatching first in the spring, with the offspring produced by that hatch, showing up in our streams in the fall.  I've said before (see the entry from 9/30/11) that I think of A. turbida as our "fall" small minnow mayfly since it's the most common Baetid that I see at this time of year.  If you look at enough small minnow nymphs, you'll come to recognize this one as soon as you see it: A. turbida nymphs are small, they have two tails, and the thorax is very broad.  This was a young one, and I'm impressed with my camera for getting fairly sharp photos.  This nymph was only 2 mm long!  At maturity, A. turbida nymphs measure 4-6 mm.  We should see a lot of them this month and next.

I was at the South river this morning, up in Greene county, where I saw very little other than common stoneflies of various sizes -- and our small minnow mayfly, of course.  Well, there were also Odontocerids (Strong case-makers) hanging around.  Curiously, they were in leaf packs; I normally see their cases on the tops of the rocks.

Some photos:

1. Common stonefly (Perlid), Paragnetina immarginata.  This is the first time I've seen these in a stream other than the Rapidan River.  Still fairly small.

2. Common stonefly, Acroneuria abnormis, one that had just recently molted -- but it's already starting to darken.

3. Odontocerids -- Strong case-maker caddisfly larvae -- Psilotreta libada.

4. And a Giant stonefly -- there are a lot of them in this stream.  This looks to be the same species that we find in Sugar Hollow, the one we think is Pteronarcys scotti (see the entry for 2/2/12), but that ID is not unproblematic.  According to Beaty ("The Plecoptera of North Carolina," p. 28), the lateral hooks on abdominal segments 6-8 of P. scotti are "appressed and not conspicuous."  On these nymphs, the hooks are clearly "appressed" on segments 7-10 -- but the hook on segment 6 is pretty darn clear to me.

And looking eye-to-eye!

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