Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
This one seems to tentatively key to Holocentropus, although I can't make out the anal spines in Couplet 7 of the Key to Genera of Polycentropodidae Larvae nor the dark bands in Couplet 4 of the Key to Genera of Polycentropodidae Larvae, making me wonder if I went wrong somewhere in keying it out. I don't see where that could have happened, though. It might also be that it's a very immature larva and doesn't possess all the identifying characteristics in the key yet. If Holocentropus is correct, then Holocentropus flavus and Holocentropus interruptus are the two likely possibilities based on range, but I was not able to find a description of their larvae.
July 9th was the fishiest day of the wife-oriented portion of this Montana trip. After a late-morning start, we drove the scenic highway from Philipsburg to Rock Creek and then down the valley to a spot that fished really well last year. My backpack included a Jetboil, can of Campbell's chicken noodle soup, a Mountain House meal, tea, apples, a large book about genetics, and several other unconventional amenities designed to keep everybody happy on the river for 8+ hours. It worked, I think.
The fishing was good for most places and alright for here. Nymphs were surprisingly ineffective and most fish rose to dries instead. I caught quite a few decent cutthroat and brown trout, along with one brookie, although nothing exceeded 15 inches. Rainbows remained in hiding. Lena caught a nice cutthroat, too.
I lost track of this specimen before I could get it under my microscope, but caddis expert Dave Ruiter was able to identify it from pictures as Glossosoma, with an uncertain suggestion of G. alascense as the most likely species.
Troutnut on Jul 25, 2019July 25th, 2019, 5:31 am EDT
Montana had that late snow pack, too. Some rivers were more out-of-shape from it than others. Rock Creek was high, but it's pretty resilient and stays in fishable condition with some extra water.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist