As I left the upper Doyles River this morning, I had this entry all figured out. It would feature this flatheaded mayfly which I was sure was M. ithaca, and illustrate how we ID it. Unfortunately, my stream side identification was wrong: this appears to be a species I've not seen before, Maccaffertium mediopunctatum. Here is Beaty's description:
M. mediopunctatum -- nymphs 7-10 mm; 0-9 (usually less than 5) hairs, 4-8 (usually 5-6) spine-like setae on maxillary crown; posterolateral projections present anterior to segment 6; sternal maculations variable though usually with dark crossbands on sterna 2-8, and 9 with dark, inverted "U". Found in the mountains only, especially rivers. ("The Ephemeroptera of North Carolina," p. 19)
1. Our nymph measured ~8 mm.
2. While I could not get a good photo of the maxillary crown, I counted 5 spine-like setae and about 8 hairs.
3. the posterolateral projections, the dark crossbands on sterna 2-8 (can only see them on 3-8 on our nymph), and the inverted "U" on sterna 9 can all be seen in this microscope photo.
It clearly is not M. ithaca, which measures 9-14 mm with transverse sternal bands only on segments 5-6 or 7-8.
To me, the evidence for M. mediopunctatum seems very strong. Still I'll probably check this with Beaty when he returns from vacation. There is another possibility: M. modestum.
The rest of the insects I picked up today were fairly predictable for this time of year.
1. Perlodid stonefly, Diploperla duplicata.
2. Perlodid stonefly, Isoperla holochlora. Lots of them in the leaf packs.
3. And of course, I found a lot of E. dorothea spiny crawlers.
With Patricia Byrom Park just a few miles up the road, I continued on to see what I could find in the small mountain stream that flows next to the car park. Not a whole lot of success.
1. I saw a couple of Eccoptura xanthenses common stones, this one fairly mature.
2. The case-maker Pycnopsyche gentilis.
3. And to my surprise, there were still Uenoids on the rocks in this stream. This one was N. mitchelli.
Another Mac from the Doyles which I think might be a young mediopunctatum, though I need to look it over with care.
Monday, up the Rapidan River!
Addendum: Well, I see that on 6/14/12 I concluded that this nymph was, indeed, M. ithaca! I plan to send it to Beaty and see what he has to say.