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Mayfly Species Drunella flavilinea (Flav)

Pictures Below
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

Region: West

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

Habitat: Quiet water adjacent to the fast-water nymphal habitat

Water Temperature: 55-57F
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.

Pictures of 3 Mayfly Specimens in the Species Drunella flavilinea:

Drunella flavilinea (Flav) Mayfly NymphDrunella flavilinea (Flav) Mayfly Nymph View 6 PicturesAlthough the identification is not certain because the nymph is not yet mature, the configuration of tubercles (
A few (not all) of the abdominal tubercles on this Ephemerella needhami nymph are circled.  They are especially large in this species.
A few (not all) of the abdominal tubercles on this Ephemerella needhami nymph are circled. They are especially large in this species.
Tubercle: Various peculiar little bumps or projections on an insect. Their character is important for the identification of many kinds of insects, such as the nymphs of Ephemerellidae mayflies.
on this one--particularly the forefemora--seems to best match Drunella flavilinea.
Collected July 2, 2019 from the Gallatin River in Montana
Added to by Troutnut on July 18, 2019
Female Drunella flavilinea (Flav) Mayfly DunFemale Drunella flavilinea (Flav) Mayfly Dun View 6 PicturesI 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.
Collected July 31, 2020 from the Henry's Fork of the Snake River in Idaho
Added to by Troutnut on August 16, 2020

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