That flatheaded mayfly just got a little too close! Rhyacophilids are predaceous. Had I not broken this up, that flathead would have been missing a leg.
Close call! This free-living caddis is one that we see fairly often in small mountain streams: Rhyacophila nigrita. The dark front edge of the pronotum is a fairly good clue. This was a big one -- ~20 mm -- and chubby as well, and it was one of three species of Rhyacophila I saw today at Entry Run. The other two: R. fuscula (the green one with the topless "H" on the head), and Rhyacophila sp. This one.
No guess yet on the species ID: I'll need some time. It may be one we've not seen before.
As for the flatheaded mayfly in that photo at the top of the page, it belongs to the "group" Epeorus pleuralis, but the species is Epeorus fragilis. For the distinction, Look back to my posting of 5/26/13. Here's a better look at our mayfly.
And this is Epeorus pleuralis.
The difference is in the head. With Epeorus fragilis, the edge/margin of the head separates abruptly from the eye, and there's a distinct anteromedial "V". The posterolateral margin of the head is essentially covered by the eye.
By contrast, on Epeorus pleuralis, the posterolateral margin of the head is exposed.
As you know, Epeorus pleuralis is common right now in all of our good mountain streams, with nymphs covering the bottoms of rocks. Why Epeorus fragilis shows up as well in this particular watershed -- Entry Run/South River -- is something I need to explore.
I was investigating new water this morning: I drove up Entry Run Rd. as far as I could go making a good jump in elevation. The water was small and crystal clear.
I photographed quite a few insects, but the photos just didn't turn out. One of those days. But you can be sure I'll return later on in the spring.