Header image
Enter a name
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 Holocentropus (Polycentropodidae) Caddisfly Larva from the Yakima River in Washington
This one seems to tentatively key to Holocentropus, although I can't make out the anal spines in Couplet 7 of the Key to Genera of Polycentropodidae Larvae nor the dark bands in Couplet 4 of the Key to Genera of Polycentropodidae Larvae, making me wonder if I went wrong somewhere in keying it out. I don't see where that could have happened, though. It might also be that it's a very immature larva and doesn't possess all the identifying characteristics in the key yet. If Holocentropus is correct, then Holocentropus flavus and Holocentropus interruptus are the two likely possibilities based on range, but I was not able to find a description of their larvae.
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.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Male Epeorus longimanus (Slate Brown Dun) Mayfly Dun Pictures

Identification of this one was as follows. Body 9 mm, wing 11 mm.
Both Epeorus albertae and Epeorus dulciana should have a conspicuously darkened humeral crossvein in the forewing. This one doesn't.
The foretarsal claws are dissimilar (one sharp, one blunt), which also rules out the Epeorus albertae group.
The dark macula on the forefemora rules out Epeorus deceptivus, which is also supposed to be a little bit smaller.
Both Epeorus grandis and Epeorus permagnus should be much, much larger.
Of the species known to be present in Washington, this leaves only Epeorus longimanus, which is exactly the right size. The key to male spinners in Traver (1935) describes distinctive markings that are visible (although more faintly) in this dun: “Black posterior margins of tergites do not extend laterally to pleural fold, but an oblique black line form this margin cuts across poster-lateral triangle to pleural fold.”

Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Lateral view of a Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Ruler view of a Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington The smallest ruler marks are 1 mm.
Ventral view of a Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Dorsal view of a Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington

This mayfly was collected from Mystery Creek #295 in Washington on May 31st, 2022 and added to Troutnut.com by Troutnut on June 1st, 2022.


Start a Discussion of Dun

Male Epeorus longimanus (Slate Brown Dun) Mayfly Dun Pictures

Collection details
Location: Mystery Creek #295, Washington
Date: May 31st, 2022
Added to site: June 1st, 2022
Author: Troutnut
Troutnut.com is copyright © 2004-2024 (email Jason). privacy policy