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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
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.

Dorsal view of a Setvena wahkeena (Perlodidae) (Wahkeena Springfly) Stonefly Nymph from Mystery Creek #199 in Washington
As far as I can tell, this species has only previously been reported from one site in Oregon along the Columbia gorge. However, the key characteristics are fairly unmistakable in all except for one minor detail:
— 4 small yellow spots on frons visible in photos
— Narrow occipital spinule row curves forward (but doesn’t quite meet on stem of ecdysial suture, as it's supposed to in this species)
— Short spinules on anterior margin of front legs
— Short rposterior row of blunt spinules on abdominal tergae, rather than elongated spinules dorsally
I caught several of these mature nymphs in the fishless, tiny headwaters of a creek high in the Wenatchee Mountains.
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.
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Western Green Drakes

Like most common names,"Western Green Drake" can refer to more than one taxon. They're previewed below, along with 10 specimens. For more detail click through to the scientific names.

Mayfly Species Drunella doddsii

These are pretty much always called Western Green Drakes.
This species together with the Drunella grandis sub-species make up the Western Green Drake hatch. Besides being smaller, the adults are difficult to tell apart from it's larger siblings; but D. doddsi nymphs have a few peculiar traits that set them apart. D. doddsi looks much thicker in the thorax, has a flat frontal head margin and a unique oval disk-like ring of hairs on its ventral surface. However, There are very few differences between the habits of these two species, and they are almost always discussed together in fly fishing books, so for many of the characteristics of doddsii, refer to the Drunella grandis page.
Lateral view of a Male Drunella doddsii (Ephemerellidae) (Western Green Drake) Mayfly Dun from the Gulkana River in Alaska
Dorsal view of a Drunella doddsii (Ephemerellidae) (Western Green Drake) Mayfly Nymph from the Gulkana River in Alaska

Mayfly Species Drunella grandis

These are pretty much always called Western Green Drakes.
This species (or rather group of subspecies), together with Drunella doddsii, make up the famous Western Green Drake hatches. They are widespread throughout the vast Western region and can be abundant enough in many locations to provide world class angling.

It hasn't been all that many years since Western traditions and entomological "facts on the ground" began to influence the angler's lexicon heavily dominated by Eastern writers. Their initial reporting after visiting the region first popularized the phrase "Rocky Mountains answer to the popular Green Drakes of the East". This led to a false impression that lingers to this day. The reality is these giants of their family have abundant populations all over the West with no counterpart in the East, and the West does have abundant hatches of comparable Ephemeridae. The Western tradition of naming outsized Mayflies "Drakes" is the reason for what many consider a misnomer by giving it the same common name as the legendary Ephemerid of the East and surely contributed to confusion for anglers unconcerned with such subtleties.
Lateral view of a Female Drunella grandis (Ephemerellidae) (Western Green Drake) Mayfly Dun from the American River in Washington
I collected this specimen while away from all my good photography equipment except the camera and one of my macro lenses, so I made do. The lighting is from lamps in a hotel room, so it was hard to edit for really true colors, but I tried to get as close as possible. The body was 13 mm long, wing 19 mm long.

Mayfly Species Drunella coloradensis

These are very rarely called Western Green Drakes.
This species is very similar to Drunella flavilinea. In areas where their ranges overlap, they can sometimes be found in the same streams. They are similar enough that anglers sometimes refer to either or both species as "Flavs." Allen and Edmunds (1962) say that Drunella coloradensis tends to favor colder water than Drunella flavilinea and that it may emerge as much as a month later.
Lateral view of a Male Drunella coloradensis (Ephemerellidae) (Small Western Green Drake) Mayfly Dun from Mystery Creek #199 in Washington
The positive species ID on this dun comes from both the spinner that it (or possibly one other dun just like it) molted into and the overwhelming abundance of nymphs of this species in my kicknet samples from the same site.
Lateral view of a Male Drunella coloradensis (Ephemerellidae) (Small Western Green Drake) Mayfly Spinner from Mystery Creek #199 in Washington
This spinner molted from this dun, or possibly one other dun I had in the same container that looked just like it.
Dorsal view of a Drunella coloradensis (Ephemerellidae) (Small Western Green Drake) Mayfly Nymph from Mystery Creek #249 in Washington
This one nicely illustrates the variation in coloration within an single Ephemerellid species in a single stream, when compared to its lighter, banded counterpart.

Mayfly Species Drunella flavilinea

These are very rarely called Western Green Drakes.
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.
Artistic view of a Male Drunella flavilinea (Ephemerellidae) (Flav) Mayfly Dun from the Cedar River in Washington
This dun is smaller than would normally be expected for Drunella flavilinea, 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.
Male Drunella flavilinea (Ephemerellidae) (Flav) Mayfly Spinner from the Flathead River-lower in Montana
Dorsal view of a Drunella flavilinea (Ephemerellidae) (Flav) Mayfly Nymph from the Cedar River in Washington
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