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Artistic view of a Male Pteronarcys californica (Pteronarcyidae) (Giant Salmonfly) Stonefly Adult from the Gallatin River in Montana
Pteronarcys californica

The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.

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.

Mayfly Species Ephoron leukon (White Flies)

See the main Ephoron page for details about this species, which is not known to differ in any important ways (besides location) from the other species.

On page 243 of Hatches II there is a passage from an 1802 speech before the American Philosophical Society in which this mayfly was introduced to science. It was the first mayfly species described in the United States, so it is ironic that it went unnoticed through so many of the early decades of our sport.

Where & when

This is the only Ephoron species producing significant hatches in the East, and it overlaps with Ephoron album in the Midwest.

In 27 records from GBIF, adults of this species have mostly been collected during August (41%), July (26%), September (15%), and June (11%).

In 1 record from GBIF, this species has been collected at elevation of 618 ft.

Species Range


Quoting The Biology of Mayflies regarding the adults:
This species differs from E. album in the deep red-brown mesonotum; smoky pronotum and reddish brown markings on pleura and sternum; darker fore legs; area of dark cross veins in fore wing more extensive; tails darker; tergites shaded with grey. The body, in individuals measured, is slightly longer.

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: 13–14 mm
Wing length: 11–12 mm

Vertex of head yellowish brown, heavily shaded with purplish black between ocelli; mesonotum largely dark reddish brown; veins of costal margin of fore wing purplish, cross veins of median and cubital areas greyish lavender. Face yellowish; antennae pale whitish, faint grey shading at apex of second joint; eyes black. Vertex yellowish to pale reddish brown, heavily shaded with purplish black between ocelli, often with faint brown shading near posterior margin; bases of ocelli heavily black-ringed. Pronotum yellowish brown, tinged distinctly with purplish grey in median area; reddish brown shading laterally; purplish grey streaks and shading above base of fore leg. Mesonotum dark red-brown in anterior and median portions; posterior portion anterior to and laterad of scutellum pale yellowish; scutellum smoky; sutures and a narrow median line blackish, except in anterior portion, where median line is yellow. Metanotum red-brown, scutellum dark smoky. Pleura yellowish with red-brown areas anterior to middle leg and below wing roots; sternum yellow, washed with red-brown in median area. Fore femur and tibia deep purple, the femur with whitish areas along ventral edge and near middle of outer surface; tarsus paler, purplish grey. Middle and hind femora yellowish, tibiae and tarsi whitish. Wings as in E. album Say, but both longitudinal and cross veins of costal margin are darker, cross veins appearing blackish in some lights; cross veins as far back as the anal region are purplish grey, becoming fainter and paler posteriorly. Abdomen yellowish white; basal and middle segments often semi-hyaline; segments 8-10 yellowish with tinge of red, the tergites washed with purplish grey except on lateral margins, this shading deepest in median area and anterior margin. Middle tergites with a greyish median streak, sometimes faintly seen also on basal tergites; occasional traces also of grey shading laterally. Genitalia pale; tips of penes and tip of long joint of forceps dusky. Tails rather deep purplish at base, becoming pearly grey in median area, tips whitish; joinings opaque white.

Discussions of Ephoron leukon

Posted by Imaxfli on Oct 23, 2020
Last reply on Oct 23, 2020 by Imaxfli
Me too looking for photos or better yet, video of matching. These things seem to pop outa the water like no other ......
Ephoron Leukon nymph photographs
11 replies
Posted by BFornadley on Feb 8, 2007
Last reply on Aug 14, 2007 by Gene
I need some help here. I have been looking all over the web for someone who may have taken some Ephoron Leukon nymph underwater (or out of water) photos.I saw the description here at "Troutnut.com" and advice that a smaller Brown Drake (Ephemera) nymph would be a good natural to use as a tying model but I really want to see the real thing. Does any body have any of these pics or can anyone definitively tell me where to look?

Start a Discussion of Ephoron leukon


  • Caucci, Al and Nastasi, Bob. 2004. Hatches II. The Lyons Press.
  • Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.

Mayfly Species Ephoron leukon (White Flies)

Species Range
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