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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Dorsal view of a Grammotaulius betteni (Limnephilidae) (Northern Caddisfly) Caddisfly Larva from the Yakima River in Washington
This is a striking caddis larva with an interesting color pattern on the head. Here are some characteristics I was able to see under the microscope, but could not easily expose for a picture:
- The prosternal horn is present.
- The mandible is clearly toothed, not formed into a uniform scraper blade.
- The seems to be only 2 major setae on the ventral edge of the hind femur.
- Chloride epithelia seem to be absent from the dorsal side of any abdominal segments.
Based on these characteristics and the ones more easily visible from the pictures, this seems to be Grammotaulius. The key's description of the case is spot-on: "Case cylindrical, made of longitudinally arranged sedge or similar leaves," as is the description of the markings on the head, "Dorsum of head light brownish yellow with numerous discrete, small, dark spots." The spot pattern on the head is a very good match to figure 19.312 of Merritt R.W., Cummins, K.W., and Berg, M.B. (2019). The species ID is based on Grammotaulius betteni being the only species of this genus known in Washington state.
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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Ephemerella aurivillii Mayfly Nymph Pictures

Artistic view of a Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Chena River in Alaska
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Chena River in Alaska
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Chena River in Alaska
Dorsal view of a Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Chena River in Alaska
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Chena River in Alaska
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Chena River in Alaska
Ruler view of a Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Chena River in Alaska The smallest ruler marks are 1 mm.

This mayfly was collected from the Chena River in Alaska on May 10th, 2008 and added to Troutnut.com by Troutnut on April 20th, 2011.

Discussions of this Nymph

E. aurivillii
1 replies
Posted by Entoman on Apr 26, 2011
Last reply on Apr 26, 2011 by Troutnut
Jason,

I was going to share my belief that this specimen is E. aurivillii, but I see you beat me to it.:) Oh well, with all the "fast gun" Bugmeisters on this site, there are really only two types, "the quick and the dead!":)

This species is fairly common in the West, but nobody seems to know what the duns look like. If you could catch some ripe nymphs this spring and hatch them into duns, it would be excellent reportage.

Regards,

Kurt

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Ephemerella aurivillii Mayfly Nymph Pictures

Collection details
Location: Chena River, Alaska
Date: May 10th, 2008
Added to site: April 20th, 2011
Author: Troutnut
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