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.
John S, when the rising ceased, I did run a Sawyer pheasant tail down through a couple runs, but to no avail. Perhaps the fish were full. For a moment I thought about trying a scud or egg, but the draw of rising fish had me off searching other sections of the stream. But it wasn't until the sun began to set, that midges and a few more baetis brought more fish to the surface.
Yes, there may be a "smorgasbord" of nymphs and larvae at this time of year, but the explanation also seems to suggest that those benthic invertebrates are constantly available to the trout and easy to capture. Surely, the early Spring underwater smorgasbord also includes some relatively large and meaty items (at least, compared to the little baetids). If these items are readily available for easy capture, it seems to beg the question of why the trout would rise to the little baetids in the first place.
Thanks, Kinzua. I think the scud was a probably good idea, but I'm just very partial to them on limestone waters in general. As John suggests, however, my explanation is also subject to exceptions and a high degree of uncertainty. I just like to quibble to pass the time when I can't fish. ;)