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.
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.