Frustrating! The Rivanna at Crofton is still too high for me to reach the riffles that I want to explore. And I'm keen to look on those rocks since that's where I found this unusual small minnow mayfly last autumn -- on September 14th, to be exact. This is Heterocloeon petersi, and it's one of three small minnow mayflies (Baetidae) that, to date, I've only seen in the Rivanna. The others -- Iswaeon anoka and Labiobaetis propinquus.
From sampling this river in years past as a stream monitor, I know that the Rivanna has a good population of small minnow mayflies each summer. I don't recall seeing many at all in the spring and fall; I don't think I've ever looked in the winter (usually too high or too cold).
To date, these are the Rivanna small minnow mayflies that I've found: I hope to find more in the future.
1. Acentrella turbida. Tolerance value, 2.0. Rivanna at Darden Towe
2. Baetis intercalaris. Tolerance value, 5.0. Rivanna at Crofton and Darden Towe
3. Heterocloeon petersi. Tolerance value TBD. Rivanna at Crofton. Vulnerable to extirpation. (also pictured at the top of the page)
4. Heterocloeon curiosum. Tolerance value, 2.1. Rivanna at Crofton and Darden Towe.
5. Iswaeon anoka. Tolerance value, 4.4. Rivanna at Darden Towe. Uncommon.
6. Labiobaetis propinquus (formerly Pseudocloeon propinquum). Tolerance value, 5.8. Rivanna at Crofton.
Hoping to report on the Rivanna at Crofton sometime next week. I'll also be looking for this unusual common stonefly which, to date, I've only found there. Agnetina annulipes.
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