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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 Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
This specimen appears to be of the same species as this one collected in the same spot two months earlier. The identification of both is tentative. This one suffered some physical damage before being photographed, too, so the colors aren't totally natural. I was mostly photographing it to test out some new camera setting idea, which worked really well for a couple of closeups.
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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Mayfly Species Isonychia intermedia (Slate Drakes)

Species Range

Physical description

Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.

Male Spinner

Body length: 12 mm
Wing length: 12 mm

A dark purplish red species, having pale antero-lateral triangles on the abdominal segments; venation dark brown.

Thoracic notum intense raw-umber brown, somewhat paler before the scutellum of the mesonotum. Fore leg about 2/3 as long as the body. Femur and tibia dark brown, femur rather paler at base; tarsus light brownish red, the first joint yellowish. Middle and hind legs light yellow, the claws and tarsal joinings narrowly purplish brown. Wings hyaline, venation dark brown; large longitudinal veins paler toward the wing base.

Abdomen intense purplish red. Tergites with yellowish white triangles occupying the antero-lateral angles, and between these and the median line another pale streak at the anterior margin. These spots increase in size posteriorly. Smaller pale triangles occupy the antero-lateral angles of the sternites. Sternite 10 and the forceps dull yellowish brown, washed with reddish purple; forceps base purplish red. Apical margin of the forceps base deeply excavated as in Isonychia sicca.

Start a Discussion of Isonychia intermedia


  • Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.

Mayfly Species Isonychia intermedia (Slate Drakes)

Species Range
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