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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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Male Callibaetis (Speckled Dun) Mayfly Spinner Pictures

This is a tricky one to ID. The forewings seem to be on the low end of the "crossvein count" key characteristic. There are paired marginal intercalaries in the middle area of the fore wing (kind of visible in photos, verified 100 % under microscope), and the wing and its veins are pale. Keys would seem to point to Callibaetis pictus in this case, but several other characteristics including size don't fit (pictus is smaller), and this is a bit out of its range.

Lateral view of a Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin
Artistic view of a Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin
Ruler view of a Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin The smallest ruler marks are 1 mm.
Ventral view of a Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin
Dorsal view of a Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin
I really cranked up the contrast on the wing veins because they were incredibly difficult to see otherwise.

Male Callibaetis (Baetidae) (Speckled Dun) Mayfly Spinner from the Teal River in Wisconsin

This mayfly was collected from the Teal River in Wisconsin on June 10th, 2021 and added to Troutnut.com by Troutnut on June 11th, 2021.


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Male Callibaetis (Speckled Dun) Mayfly Spinner Pictures

Collection details
Location: Teal River, Wisconsin
Date: June 10th, 2021
Added to site: June 11th, 2021
Author: Troutnut
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