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.

I spent more than an hour casting to several rising trout in this pool and caught only two. Its clear water and tricky currents harbor dozens of free-rising, usually very hard-to-catch fish.

From Enfield Creek in New York

Stream photos

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Onocosmoecus (Great Late-Summer Sedge) Caddisfly Larva Onocosmoecus (Great Late-Summer Sedge) Caddisfly Larva

Lateral view of a Onocosmoecus (Limnephilidae) (Great Late-Summer Sedge) Caddisfly Larva from the Yakima River in Washington

This specimen keys pretty easily to Onocosmoecus, and it closely resembles a specimen from Alaska which caddis expert Dave Ruiter recognized as this genus. As with that specimen, the only species in the genus documented in this area is Onocosmoecus unicolor, but Dave suggested for that specimen that there might be multiple not-yet-distinguished species under the unicolor umbrella and it would be best to stick with the genus-level ID. I'm doing the same for this one.

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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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Male Rhithrogena morrisoni (Western March Brown) Mayfly Spinner Pictures

Lateral view of a Male Rhithrogena morrisoni (Heptageniidae) (Western March Brown) Mayfly Spinner from the South Fork Snoqualmie River in Washington

Dorsal view of a Male Rhithrogena morrisoni (Heptageniidae) (Western March Brown) Mayfly Spinner from the South Fork Snoqualmie River in Washington

Male Rhithrogena morrisoni (Heptageniidae) (Western March Brown) Mayfly Spinner from the South Fork Snoqualmie River in Washington

Ventral view of a Male Rhithrogena morrisoni (Heptageniidae) (Western March Brown) Mayfly Spinner from the South Fork Snoqualmie River in Washington

Ruler view of a Male Rhithrogena morrisoni (Heptageniidae) (Western March Brown) Mayfly Spinner from the South Fork Snoqualmie River in Washington The smallest ruler marks are 1/16".

This mayfly was collected from the South Fork Snoqualmie River in Washington on June 22nd, 2017 and added to Troutnut.com by Troutnut on June 23rd, 2017.

Discussions of this Spinner

Second opinions on this one's ID?

3 replies

Posted by Troutnut on Jun 23, 2017

Last reply on Jul 5, 2017 by Crepuscular

I tentatively keyed it out to Rhithrogena morrisoni based on Needham's Biology of Mayflies, but I'm not completely sure. Roger's website lists Rhithrogena emerging in Washington in March and April, and this one was collected June 22nd. But this did come from high up in a mountain stream after a year of very heavy snowpack, so it might be that far behind schedule. It also looks very much like the specimen Bob Newell posted from eastern Washington. What do Roger and others think?

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