Header image
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.

> The South Fork Sauk River

Landscape & scenery photos from the South Fork Sauk River

Closeup insects by Troutnut from the South Fork Sauk River in Washington

Male Rhithrogena virilis  Mayfly Spinner
I'm fairly sure this is a specimen of Rhithrogena virilis based on closeup examination of the reproductive anatomy under the microscope (not shown in photos). The other other species of Rhithrogena this large is Rhithrogena flavianula, but the key in Needham's Biology of Mayflies mentions annulation in the abdomen (visible in some images on bugguide.net) more distinct than that on this specimen.

The body and front wing were both about 15.5 mm long, while the cerci were 40 mm long.
Male Epeorus deceptivus  Mayfly Dun
The lack of a darkened humeral crossvein rules out Epeorus albertae and Epeorus dulciana. The lack of a dark macula on the forefemora rules out Epeorus longimanus. The small size rules out Epeorus grandis and Epeorus permagnus. That leaves as the only possibility known in Washington state Epeorus deceptivus. It is a small species, although not reportedly quite as small as this specimen. I couldn't find anything in the species description in Traver (1935) to definitively confirm or rule out the species ID, given that I don't have the preserved specimen to check under a microscope, but it has to be either deceptivus or something not yet reported in Washington.

It was collected at the same time as a similar-sized female dun.
Female Epeorus deceptivus  Mayfly Dun
I'm guessing this female is of the same species as this male dun, because they came from the same pool at the same time and the size matches, although the males and females would look very different in this case.
Troutnut.com is copyright © 2004-2023 (email Jason). privacy policy