The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
Here's a Baetid nymph close to hatching, with darkened wingpads. It's got dark bands on the tail at the middle and tip, a rounded, oval 7th gill, and gill veinlets which are visible but not conspicuous.