Thursday, April 5, 2012
Buck Mt. Creek -- and "Yes," the Small Minnow Mayfly, Acentrella turbida, is a Bi-brooded Insect
The small minnow species, Acentrella turbida, is one that I expect to see in our streams in the fall (Lynch River, Moormans River, Buck Mt. Creek). But if you look back to the entries posted on 9/30 last year, you'll see that I had started to think that it might be a "bi-brooded" species -- that is, we have an A. turbida hatch in the spring followed by a second hatch in the fall. I now know for sure that that is true.
I found three A. turbida nymphs this morning at Buck Mt. Creek. They were tiny -- about 4mm -- but this is a tiny insect. Here's a photo of one of the many that I found last fall (lots of photos of them posted in the entries in October last year). This photo was taken on 10/21.
One of the features that gives this species away is the broad thorax -- upper body and wing pads: most small minnow mayflies have a more "streamlined" appearance. But the defining characteristic requires microscope work. Quoting Beaty ("The Ephemeroptera of North Carolina," p.4): "dense row of long setae on dorsal margins of tibiae and tarsi." The long setae is pretty clear in this photo:
I'm not sure how I missed these last spring in our streams. But when I looked back at spring photos in my 9/30 entry last fall, I thought that I had seen some samples. Clearly I had.
But I had two other "surprises" this morning. The first: I found my first Epeorus vitreus flatheaded mayfly of the new season.
Note how this contrasts with the Epeorus pleuralis nymphs we've been finding in large numbers for over two months.
The color is different, and the head is not shaped the same. But look at the difference in gills! Much larger gills on E. vitreus with very marked tracheation. Still, Beaty tells us that we have to look at the front of the head when we're picking out E. vitreus nymphs: "head with distinctive color pattern of four irregular pale spots on anterior margin of head..." ("The Ephemeroptera of North Carolina," p.17) And there they are.
Epeorus vitreus hatches in late May through early August as the "Gray-winged Yellow Quill"; the hatch of Epeorus pleuralis (the "Quill Gordons") has already started and will continue through May. Buck Mt. Creek is the only stream in which I found E. vitreus nymphs last spring: that was in May.
The second: sorry, it's a microscope photo.
Never saw this one until I was looking at some nymphs I had brought back with me to examine. It's a very small/young common stonefly (Perlid), genus Perlesta! The first time I found one last spring was on June the 6th -- and it was in Buck Mt. Creek.
But if you look through the entries from June and July of last year, you'll see that I then started to see them in all sorts of streams. We spot Perlesta in two different ways. 1) They have an irregular row of spinules at the back edge of the head. This:
And 2) there are subanal gills present. You can make them out -- just barely -- in the photos posted above. Also, note how the bodies are "freckled." This is especially noticeable on immature nymphs.
They turn into beautiful stoneflies.
So, it was another eventful day at Buck Mt. Creek, and I got some decent photos even though I was working in low light conditions. The dominant insects? Spiny crawler mayflies -- scads of them! Coming in second would be the Perlodid stoneflies, Isoperla namata and Diploperla duplicata. But I also found a fair number of Nemourids today, genus Amphinemura. (Note the "cervical" gills sticking out from both sides of the neck.)
Epeorus vitreus nymph staring us down!