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Mayfly Species Epeorus longimanus (Slate Brown Dun)

Pictures Below ↓
Epeorus longimanus and Epeorus albertae are the two most common Epeorus species in the West.  

Where & When


Region: West

Time Of Year (?): June through mid-August, peaking in mid-June to mid-July, for about one week in any given location

Altitude: Above 5,000 feet
According to Ernest Schweibert in Matching the Hatch, the trout "respond very well" to this hatch. Fred Arbona in Mayflies, the Angler, and the Trout called the hatches disappointing, noting that they may be overshadowed by simultanenous hatches of Rhithrogena hageni.

Hatching Behavior


Time Of Day (?): Anytime; sometimes concentrated in late morning

The nymphs emerge sporadically on the bottom in the shallows and rise to the surface as duns.

Spinner Behavior


Time Of Day: Midday

Habitat: Fast water

Nymph Biology


Current Speed: Fast

This species is found more in the cold headwaters than Epeorus albertae and Epeorus grandis.

Pictures of 3 Mayfly Specimens in the Species Epeorus longimanus:

Epeorus longimanus (Slate Brown Dun) Mayfly NymphEpeorus longimanus (Slate Brown Dun) Mayfly Nymph View 2 Pictures
Collected June 24, 2005 from the Vermillion River in Montana
Added to Troutnut.com by Bnewell on June 27, 2011
Female Epeorus longimanus (Slate Brown Dun) Mayfly SpinnerFemale Epeorus longimanus (Slate Brown Dun) Mayfly Spinner View 1 PicturesI associated this female with a male I collected one night later. For a great and informative discussion of all Epeorus species and other mayflies be sure and read, WESTERN MAYFLY HATCHES by R. Hafele and D. Hughes. They rate all of the western mayflies and they rate the hatch of this genus a 25 out of a possible 45 points based on several rating criterion. They provide insect photos, possible fly patterns and fly presentations. This is a great book.
Collected July 24, 2011 from the Touchet River in Washington
Added to Troutnut.com by Bnewell on July 25, 2011
Female Epeorus longimanus (Slate Brown Dun) Mayfly SpinnerFemale Epeorus longimanus (Slate Brown Dun) Mayfly Spinner View 2 Pictures
Collected July 26, 2011 from the Touchet River in Washington
Added to Troutnut.com by Bnewell on July 26, 2011

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