Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York

Blue-winged Olives
Baetis

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.

Stream photos

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Male Ameletus vernalis (Brown Dun) Mayfly Nymph Male Ameletus vernalis (Brown Dun) Mayfly Nymph

Dorsal view of a Male Ameletus vernalis (Ameletidae) (Brown Dun) Mayfly Nymph from the Icicle River in Washington

Keying this one out using Zloty & Pritchard 1997:
-No ganglionic markings on sternites 2–8
-Posterior margins of sternits 6–8 without numerous spines
-Mesal gill extension well developed (I really don't like the "well developed" language when it's subjective, but in this case the other option doesn't lead anywhere productive)
-Tails pale in basal 1/3
-Larger species (13–16 mm) — this one is just shy of 12 mm, but closer to 13 than to <10
-Spring emergence
This all points to Ameletus vernalis.

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27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.

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