They probably are. Let me simply review the insects I found today in the small stream to which I went on March 4th of this year for the very first time -- and I'll tell you their tolerance values. The dominant taxon today: the Chloroperlid (Green) stonefly (photo above): TV = 0.2 (Sweltsa species). A close second and third: the Giant stonefly, Pteronarcys scotti: TV = 1.8; and Roach-like stoneflies, genus Tallaperla: TV = 1.3. I also found a number of Free-living caddisflies, both Rhyacophila fuscula: TV = 1.6; and Rhyacophila nigrita: TV = 0.0. And if I'm right, I found a tiny Perlodid stonefly, Isoperla holochlora: TV = 0.0. That's pretty impressive. The only mayflies I found (I forgot to look under the rocks!) were Ameletids: at the most (if they were A. lineatus) the TV would be 2.4.
I'll come back to the "tiny Perlodids" (there were two of them) in a minute. But let me first run through some of the photos that I took today.
1. Chloroperlids: genus Sweltsa.
2. Giant stonefly: Pteronarcys scotti
ventral view, showing the thoracic gills
3. Free-living caddisfly: Rhyacophila nigrita (I found three)
4. Free-living caddisfly: Rhyacophila fuscula (a young one)
5. Large Winter stonefly: Taenionema atlanticum
and one that had recently molted
6. Ameletid mayfly (genus Ameletus)
On the Perlodid stoneflies I found -- there were several Clioperlas (that I kept out of my tray for the usual reason) and one Diploperla. And then, there were these two tiny nymphs. (Two photos of each.)
Can we determine the species? Not with any degree of finality. The genus is Isoperla for sure: the three dark bands on the abdomens are clear in each of the photos (and I checked the "Y" ridges and the laciniae). But remember that the key thing in determining species -- well, one of the key things -- is the pattern on the head. Here are some close-ups.
I'm not sure about 1. It may be Isoperla namata (see the posting for 12/22). On number 2. -- I wonder if this isn't a small Isoperla holochlora? Here's a mature I. holochlora nymph that I found in this stream on May 18th.
Note the pale dots in front of the eyes, and note how they appear to be forming on the nymph found today. And, note the pale "bell-shaped" space that lies in front of the anterior ocellus -- again, we can see that on the small nymph as well.
We'll have more challenges with small Perlodids in this particular stream as we move into spring. Remember that this is one of the streams in which I found two Isoperla Perlodids that have not yet been identified to the level of species (see the posting of 5/18).