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

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.

Dorsal view of a Holocentropus (Polycentropodidae) Caddisfly Larva from the Yakima River in Washington
This one seems to tentatively key to Holocentropus, although I can't make out the anal spines in Couplet 7 of the Key to Genera of Polycentropodidae Larvae nor the dark bands in Couplet 4 of the Key to Genera of Polycentropodidae Larvae, making me wonder if I went wrong somewhere in keying it out. I don't see where that could have happened, though. It might also be that it's a very immature larva and doesn't possess all the identifying characteristics in the key yet. If Holocentropus is correct, then Holocentropus flavus and Holocentropus interruptus are the two likely possibilities based on range, but I was not able to find a description of their larvae.
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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Millcreek has attached these 4 pictures to aid in identification. The message is below.
Female. 7 mm.
Female. 7mm.
Male. 6.5 mm.
Male. 6.5 mm.
Healdsburg, CA

Posts: 344
Millcreek on Jan 24, 2015January 24th, 2015, 1:07 pm EST
This mayfly was collected from the Russian River near Healdsburg, Ca. It's common from March through October. It's usually found in shallow water 3-12 inches deep and relatively free of silt with a bottom of sand, gravel and cobble.

It's fairly easy to identify from the dorsal side of the abdomen with section five, nine and ten being mostly light in color. It's also got a mouth with labial palpi having the inner margin of segment 2 slightly convex to nearly straight as opposed to variously concave. It also has the first gill much smaller than the others.

Descriptions to genus were from Merritt, Cummins and Berg (2008). The descriptions to species were from Morihara and McCafferty (1997) "The Baetis Larvae of North America (Baetidae: Ephemeroptera).
and MacCafferty, Meyer, Randolph and Webb (2008) "Evaluation of Mayfly Species Originally Described as Baetis Leach (Ephemeroptera: Baetidae)From California.
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