Last fall, I found six Perlodid stonefly genera -- immature nymphs -- and three species of one particular genus: Isoperla. The only Perlodid genus I have not yet discovered -- one that I did find last winter -- is the one pictured in the photo above, the genus Yugus. I found this nymph in the Rapidan River on March 24th. I hope to see it again -- but I don't think it's at all "common" in our streams.
Here is the sequence of discoveries I made in the fall (i.e. in this new season) along with photos of the immature nymphs. Keep in mind that any species of aquatic insect will first appear at different times in different streams. Things vary with location and water temperature, and I suppose the two things are related.
1. Isogenoides hansoni: 9/13, Rapidan River (the tolerance value remains undetermined)
This is a genus and species that I have only found in the Rapidan River. I found a second, larger, one on 10/21.
2. Clioperla clio: 10/25, Doyles River (tolerance value is 5.2)
This species is fairly common and shows up in large numbers in the streams that it inhabits.
This season, I've found C. clio nymphs in the Doyles River, Buck Mt. Creek, and in some of the tributaries to the Moormans. I know they are common in the Lynch River as well.
3. Helopicus subvarians: 11/3, Buck Mt. Creek (tolerance value is 1.2)
Again, not a Perlodid that I've seen in a lot of our streams. This season I've seen them in Buck Mt. Creek and the Doyles River, the same streams in which I saw them last year.
4. Diploperla duplicata: 11/8, one of the tributaries to the Moormans (tolerance value is 2.8)
This is a species that is fairly common. I found it last year in Powells Creek, Buck Mt. Creek, the Doyles River, and the Lynch River -- and probably other locations which I cannot at the moment recall!
5. Isoperla similis: 11/12, one of the tributaries to the Moormans (tolerance value 0.8)
I. similis nymphs are simply gorgeous, and I can't wait to see mature samples sometime in March. I have found this species in three different tributaries to the Moormans -- all small, clean, cold water streams: I've not seen it anywhere else.
6. Isoperla namata: 11/19, Rapidan River (tolerance value is 2.5)
You may recall that I wasn't really sure which Perlodid this was on 11/19: I felt more confident with the nymph I found on 12/13. This is the species I think of when I think of "Perlodid." We see it in a lot of our streams and in very large numbers, mostly in March and April.
7. Isoperla holochlora: 12/26, tributary to the Moormans River (tolerance value is 0.7)
I'm not 100% on this call -- but I'm fairly confident. We don't see this one a lot, and it seems to mature later than most other Perlodid species (May and June?). I've seen them in the Moormans tributaries, the Rapidan River, in Powells Creek, and in Buck Mt. Creek. Very pretty -- one of my favorites.
8. Remenus bilobatus: 12/30, Moormans River (tolerance value is 0.9)
This does not exhaust the list of Perlodids I'm hoping to find. I have yet to see Isoperla nr. holochlora -- Isoperla near holochlora (tolerance value of 0.0). Last year, I saw this only in the Rapidan River. It is indeed "close to" I. holochlora in appearance, but the head pattern is not quite the same.
And you may recall that last year I found two Isoperlas in tributaries to the Moormans that remain unidentified by the experts in terms of the species. These: