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Photo#111070
Large Stonefly - Hesperoperla pacifica

Large Stonefly - Hesperoperla pacifica
Thompson River, Sanders County, Montana, USA
May 8, 2007
Size: around 3 cm?

Images of this individual: tag all
Large Stonefly - Hesperoperla pacifica Large Stonefly - Hesperoperla pacifica Large Stonefly - Hesperoperla pacifica Large Stonefly - Hesperoperla pacifica

Moved
Thanks to both of you. I used your ID and searched some more on the interenet. I found this image, which I think is good a good enough match to move it to a species page. See West Fly

Probably Hesperoperla
With the proviso that I'm less familiar with Western species, I believe this is probably Hesperoperla pacifica. These are common Western perlids that form a loose group that anglers call "Golden Stones." The emergence of these, along with such Western perlid species as Calineuria californica and Claassenia sabulosa, is only slightly less famous than the grand emergence of the Salmonflies (Pteronarcys spp., especially Pteronarcys californica).

I've looked around for another example for comparison, and this is the best I could find. This image is not the best (dark, and not nearly as crisp as your photos), but it should serve to show similarities. Still, I wish someone who was more in tune with the Western stonies could have a look your perlid.

Perlidae
would be my guess. At 3 cm it is too small for a pteronarcid.

 
Size
I don't think I would ID based on size alone. I went from memory, and it's not very reliable.

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