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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
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.

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 8 pictures. The message is below.
Mature larva. 22 mm. In alcohol.
Mature larval case. 24 mm. In alcohol.
Mature larval case. 23 mm. (not including trailing stick). In alcohol.
Mature larva. 22 mm. In alcohol.
Mature larva. 22 mm. In alcohol.
Early instar larva. 12 mm. In alcohol.
Intermediate larval case and larva. Case shows characteristics of early instar case towards the back while incorporating flat pieces towards the front. Case 15 mm. In alcohol.
Early instar larva. Case 14 mm. In alcohol.
Millcreek
Healdsburg, CA

Posts: 344
Millcreek on Oct 30, 2014October 30th, 2014, 3:49 pm EDT
A fairly common caddisfly in smaller tributaries of the Russian River though I haven't found it in the mainstem. The larvae were identified to genus using Merritt, Cummins and Berg (2008) and Wiggins (1976). They're probably Onocosmoecus unicolor. The larvae are usually found in areas of slow current in deeper water that has undercut banks with tangles of roots or branches extending below the waterline. Sweeping along the roots or branches yields the largest numbers of larvae. Earlier instar larvae construct cases of bits and pieces of twigs and flat pieces of wood that are irregular in appearance while later instars construct a more orderly case out flat pieces of wood, often with a stick trailing out from the bottom end of the case. Most larvae were collected from February through May.
"If we knew what it was we were doing, it would not be called research, would it?"
-Albert Einstein

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