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.
In Caddisflies, Gary LaFontaine attributed the famous spring hatch on the Beaverkill (now known as the "Apple Caddis") to this species. After that publication, entomologists described that major hatch as a new species -- Brachycentrus appalachia.
Special thanks to Lloyd Gonzales, author of the excellent new book Fly-Fishing Pressured Water, for helping to sort out the Brachycentrus species and common names.