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2. Specimen Discussion
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3. Probably E. fragilis, but...

Both the process of elimination and reading published descriptions of Eastern Epeorus (pleuralis group) seem to leave fragilis as the only likely possibility for this specimen (as well as the related ones--#630, #631, and #633). The collection date is near the emergence range given for fragilis, and they match the description of this species in nearly every way except one: size.

Burian, et al. (2008) provide a key for Northeastern Epeorus adults that uses size as a significant means of distinguishing between fragilis and frisoni. They describe fragilis as less than 6.80mm. All of these specimens are larger, ranging from about 7mm-8.5mm. This puts them squarely within the range given for (the very similar) frisoni--6.83mm-9.42mm.

Although frisoni is described as being lighter in color than these specimens, two comments from the Burian publication are particularly interesting in this regard:





It would probably be reasonable to place these specimens as (size-anomalous) fragilis under the current taxonomic scheme. However, the stream in which they were captured seems to fit the above criteria pretty well. It would be very interesting to see someone like Konchu investigate this population further.

Sounds like a good fit. The size difference leaves a pretty big question mark over this ID, but for a relatively obscure species it's quite possible the full size range isn't fully documented. In such an isolated system high in the Catskills.

I can't tell the general audience where exactly these flies are from, but it's a small stream high in the Catskills that matches the description Gonzo found pretty well.