I have now seen, identified, and photographed a total of 5 genera of Perlodid stoneflies in our streams.
There may be more to be found -- but in the meantime, I thought I would sum up my results and make a few other comments.
The first time this season I saw any Perlodids was in November -- they were so small, I did not attempt identification. I found them in the Moormans River and Buck Mt. Creek.
In December, I was finding Clioperla Perlodids (as in the photo above) and in more than one stream. I have photos I took at Mechunk Creek and Buck Mt. Creek. And throughout the winter, this was the most common Perlodid genus I saw. I found them -- in addition to the two streams just mentioned -- in the Lynch River and the Doyles River -- probably elsewhere, but I no longer remember. By January, I was already seeing nymphs that were fairly mature, though the wingpads were not yet fully developed.
But the nymphs I've seen lately are fully mature -- and I suspect that this stonefly is already hatching.
In the "Tolerance Values" list that I use, North Carolina lists 1 species of Clioperla -- Clioperla clio -- which it gives a TV of 4.8.
The second genus that I saw early on in the winter was Diploperla. (Photo below.)
My first sighting of Diploperla was in Powells Creek near Crozet (February?). Since then, I've seen them in the Lynch River, and my "hidden stream" in Sugar Hollow (also the Doyles?). The nymphs that I saw were fairly developed, so this genus, too, may be an "early bird": i.e. it too may already be hatching. But, I found some again in the Powells only last week, and they were still not fully mature. So, I'm not sure of the length of the season for this particular genus. North Carolina lists 3 species of Diploperla, and the TV's range from 1.5 to 2.7.
Next, Isoperla. This is the most common genus we see in our streams, and I started to see "tiny" nymphs first in February. By now, they are starting to mature very well -- note the wingpad development on the one in the picture above (Powells Creek, last week) -- but we'll be seeing them in large numbers throughout April and May. North Carolina lists 12 species of Isoperlas: the TV's range from 0 to 5.6.
This was one of the surprises for me: Perlodid stonefly, genus Yugus. I found this in the Rapidan River on March 24th. But note that it, too, seems to be fully mature -- the colors and patterns are fully developed and the wingpads fully grown out (but not yet black?). I doubt that there are many streams in central Virginia with this genus in them. North Carolina lists two different species: the tolerance value is "0".
Finally, my latest find -- genus Helopicus. This is from Buck Mt. Creek where I found a number of nymphs on Saturday -- April 2nd. I have not yet seen it anywhere else -- but I'll be looking! North Carolina lists 2 species of this particular genus: the tolerance values are "0" and ".8".
Fly fishermen get excited about only one of these genera -- Isoperla. Isoperla Perlodids hatch as "Yellow Sallies," typically from July to September out West. It would be nice to know more about all Perlodid genera in terms of life cycles and know when they first appear in our streams -- what month of the year -- and when they fly off as adults. So many projects -- so little time.
(Added 6/4/11: A sixth genus: Remenus. Found at Buck Mt. Creek on 5/31 and at a tributary of the Moormans on 6/1. See the entries posted for both of those days.