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 is the first of it's family I've seen, collected from a tiny, fishless stream in the Cascades. The three species of this genus all live in the Northwest and are predators that primarily eat stonefly nymphs Merritt R.W., Cummins, K.W., and Berg, M.B. (2019).
I believe the name was coined by British chalkstream anglers. At the time it was coined, fly-tying hooks were not made in sizes that could match these tiny mayflies. Even with an appropriate imitation, they often hatch in such great numbers that the fly is hopelessly lost among them. The Brits also call them "Broadwings" (often preceded by "those bloody...").