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Salmonflies
Pteronarcys californica

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

Mayfly Species Drunella flavilinea (Small Western Green Drake)

The Flavs pick up about a week after the closely related but larger Western Green Drakes (Drunella grandis and Drunella doddsii) finish hatching on most Western waters.

Their hatches may be complemented by simultaneous hatches of two less prolific species, Drunella coloradensis and Drunella spinifera.

Where & when

Time of year : July and August

Altitude: 4000-6000 Feet

They are reported in places from mid-June all the way through October, but they peak in most places sometime in July or August.

Hatching behavior

Time of day : Flexible, but usually in the evening

Water temperature: 55-57°F

According to Knopp & Cormier in Mayflies: An Angler's Study of Trout Water Ephemeroptera , Flavs emerge in the surface film rather than underwater like most other Drunella mayflies.

The Flav duns don't have as much difficult getting off the water as their larger brethren, but they still linger longer as duns than most mayflies and provide good dry fly action.

Spinner behavior

Time of day: Late morning, or evening

Habitat: Riffles

In Hatches II, Caucci and Nastasi say the spinner falls occur in the evenings. However, in Selective Trout, Swisher and Richards say that most of the spinners fall between 9am and 1pm and a few fall in the evening. Anglers with experience to clarify this contradiction are encouraged to write their observations in the comments.

Nymph biology

The nymphs occur in many habitats but they're most prolific in fast, rocky water.

Specimens of the Mayfly Species Drunella flavilinea

1 Male Dun
Male Drunella flavilinea (Small Western Green Drake) Mayfly Dun
This dun is smaller than would normally be expected for Drunella flavillinea, but it seems to fit the physical description of that species fairly well. I wasn't sure from the dun pictures alone, so I was hoping it would molt into a spinner. It never made it out of the dun's shuck, but it did begin the process, which allowed me with great care to tease out the last couple abdominal segments of the spinner from the still tightly attached dun shuck, enabling a more confident ID based on the shape of the spinner's penes and sub-genital plate. I also collected a nymph of flavilinea in the same river on the same evening, as well as a shed exuvium that looked large enough to belong to an emerging dun.

The other possibility I considered for a while based on the dun was Drunella pelosa, which would be the right size, but the other characteristics don't fit.
1 Female Dun
Female Drunella flavilinea (Small Western Green Drake) Mayfly Dun
I can't be certain of the ID of this female dun, but I'm calling it Drunella flavilinea for three reasons: 1) the known abundance of "flavs" on the Henry's Fork, 2) clear differences in coloration from my confirmed specimens of Drunella coloradensis, which is the main lookalike, and 3) the habitat (a sizable river in a wide mountain valley, rather than a small, high-altitude stream) suggests it's not coloradensis.
2 Nymphs
1 Male Spinner

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References

Species Range
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