Mayfly Species Drunella grandis (Western Green Drake)
Taxonomic Navigation -?-
Kingdom Animalia (Animals)
» Phylum Arthropoda (Arthropods)
» Class Insecta (Insects)
» Order Ephemeroptera (Mayflies)
» Family Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs)
» Genus Drunella (Blue-Winged Olives)
» Species grandis (Western Green Drake)
Common Names
I have not fished out West to experience this hatch, so this page relies on information collected from angling authors. Unfortunately these books conflict with each other on several points. I encourage readers who've fished this hatch to share their experiences in the comments and help clarify the information.
Where & When
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, but usually in the evening during the peak time of year
Habitat: They prefer to emerge from calm places near their fast-water nymphal habitat.
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.Habitat: They prefer to emerge from calm places near their fast-water nymphal habitat.
Water Temperature: Starts at 50°F, peaks at 55-60°F
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.
I have no personal experience fishing the West to reconcile these differences in the literature; I invite users to clarify by sharing their experiences in the comments.
Nymph Biology
Current Speed: Medium to fast
Most sources suggest these mayflies inhabit medium to fast water, but Knopp & Cormier in Mayflies: An Angler's Study of Trout Water Ephemeroptera say that Drunella grandis has "a distinct preference" for slow water.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.
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