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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.

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.
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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Eurylophella (Chocolate Dun) Mayfly Nymph Pictures

This nymph is an extremely early instar.

Dorsal view of a Eurylophella (Ephemerellidae) (Chocolate Dun) Mayfly Nymph from unknown in Wisconsin
Ventral view of a Eurylophella (Ephemerellidae) (Chocolate Dun) Mayfly Nymph from unknown in Wisconsin
Eurylophella (Ephemerellidae) (Chocolate Dun) Mayfly Nymph from unknown in Wisconsin
Eurylophella (Ephemerellidae) (Chocolate Dun) Mayfly Nymph from unknown in Wisconsin
The tick marks on the ruler are millimeters.

Ruler view of a Eurylophella (Ephemerellidae) (Chocolate Dun) Mayfly Nymph from unknown in Wisconsin The smallest ruler marks are 1 mm.

This mayfly was collected from unknown in Wisconsin on February 7th, 2004 and added to Troutnut.com by Troutnut on January 25th, 2006.

Discussions of this Nymph

hook size (and chocolate duns, and old-timey mayfly family classifications)
10 replies
Posted by Warren on Apr 12, 2007
Last reply on Apr 13, 2007 by Quillgordon
thats about a size 32 right. i dont think i have any tippet that small

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Eurylophella (Chocolate Dun) Mayfly Nymph Pictures

Collection details
Location: unknown, Wisconsin
Date: February 7th, 2004
Added to site: January 25th, 2006
Author: Troutnut
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