A closeup look at this one shows robust setae along the posterior margin of the 10th tergite. They're a little more clear under the scope than in the picture, but you can see them as short little spikes in the circled area (and a few elsewhere on that margin). I missed these the first time I tried to key this one out, because I didn't realize how subtle and difficult they can be to see.
Baetis tricaudatus (Blue-Winged Olive) Mayfly Nymph from the Yakima River in Washington
Troutnut.com is a collection of pictures and information about fly fishing. Fly fishermen, fly tiers, and trout enthusiasts of all stripes can learn more about life beneath the surface of trout streams, as well as how to better imitate aquatic insects with artificial flies to catch trout. There are aquatic insect pictures, underwater pictures, landscape pictures, and a comprehensive reference to the common names of trout stream insects.
