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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 Siphlonurus occidentalis (Gray Drake)

This is the main Western species of Siphlonurus, and probably the most productive species of that genus in America.

Where & when

Time of year : April to October; peaking in August and September

Altitude: 3,000 to 5,000 feet

This species most abundant in the late summer and early fall when few other mayflies are on the water. Its activity may last few months in a single location. There's a good chart in Knopp and Cormier's Mayflies: An Angler's Study of Trout Water Ephemeroptera detailing where and when to find this species.

Hatching behavior

Time of day : Midday

The emergence is relatively unimportant because the duns usually cawl out onto shore to hatch, but shallow nymphs may be effective when this activity is at its peak.

Spinner behavior

Time of day: Mid-morning or evening

The spinners are the most important stage of this hatch.

Specimens of the Mayfly Species Siphlonurus occidentalis

2 Male Spinners
2 Female Spinners
1 Spinner
1 Female Dun
Female Siphlonurus occidentalis (Gray Drake) Mayfly Dun
I caught this specimen two days' walk from my macro lenses, but I don't think I have a dun of this species yet, so I took the best photos I could with my iPhone.
2 Nymphs

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References

Species Range
Common Names
Resources
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