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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.

Mayfly Species Drunella grandis (Western Green Drake)

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.

Where & when

Time of year : Mid-June to mid-August, lingering into September in places

The Western Green Drakes are very widespread and important, causing some of the best fishing of the season throughout their range, from Yellowstone to California to Alaska.

Caucci and Nastasi report that this hatch begins and ends a few weeks earlier on spring creeks, where they are especially prolific, than on freestone rivers.

Hatching behavior

Time of day : Variable

Water temperature: Starts at 50°F, peaks at 55-60°F

These duns take an exceptionally long time to get airborne once they break through the surface, and they may make several clumsy attempts.

Emergence may occur late in the morning early in the year or at high altitudes, but it progresses through the afternoon and into the evening as the season heats up. Most authors suggest that the best fishing at the peak of the hatch is in the evening, but others say the best hatching is in the early to mid-afternoon. All agree that it can last for several hours on a good day.

Like all common Drunella species, these duns quickly change color once they're exposed to the air. Anglers should imitate the bright green of the freshly emergent duns rather than the dark ruddy brown color they display later.

Spinner behavior

According to Hatches II, spinner flights are most common during the day:

The initial spinner flights of these species may occur at midday. As the weather climbs into the 80's and 90's, they will progressively fall later until they occur at dusk. In August, the spinner flight may take place during mid-morning...

However, according to Mayflies: An Angler's Study of Trout Water Ephemeroptera and Mayflies, the Angler, and the Trout, the spinners are active in the middle of the night. Arbona writes:
Daytime spinner flights are very sparse for such a common species because the large spinners do not become active until well after nightfall, and ovipositing is accomplished at 4am.

Most angler reporting concurs with the latter.

Nymph biology

Current speed: Medium to fast

Most sources suggest these mayflies inhabit medium to fast water, but they are common inhabitants of many spring creeks as well. To name just a few - Hat Creek and Fall river in CA., the Metolius River in OR., and the famous Henry's Fork in ID. where they have legendary status.

Like others in the Ephemerellidae, these nymphs often swim to and from the surface several times prior to emerging, and imitating this behavior is effective in the hours before the hatch. There is also evidence that the duns often emerge subsurface as well. This is given testimony by the frequent success of emerging dun wet flies.

Drunella grandis Fly Fishing Tips

As with the Eastern hatches of Isonychia bicolor, trout become strongly conditioned to watch for these meaty duns on the surface. Their imitations make excellent attractor flies on days when their hatch is off or even after it has ended.

Specimens of the Mayfly Species Drunella grandis

3 Female Duns
1 Male Dun
Male Drunella grandis (Western Green Drake) Mayfly Dun
One picture of this specimen shows the spinner stage.
8 Nymphs

1 Streamside Picture of Drunella grandis Mayflies:

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References

Species Range
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