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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 Neoleptophlebia adoptiva (American Blue Dun)

This is the best Spring hatch after the Quill Gordons (Epeorus pleuralis) but before the Hendricksons (Ephemerella subvaria) in most parts of the East, although it can overlap with both. The Blue Quills are small mayflies (hook size 16-20) but they can hatch in incredible numbers at a time when eager trout are just beginning to look to the surface after a hungry winter.

Where & when

Time of year : April through early June

The hatch begins in early April in the southern Appalachians. By late April or early May it is in Pennsylvania, and it peaks in the Catskills in early May. By late May it has moved into the Upper Midwest and the Adirondacks, where it may linger through early June. The peak hatching lasts nearly a week in most places.

One source, Mayflies of Michigan Trout Streams, says the hatch may last until July 8th, but I have found no other accounts of such late adoptiva hatches.

Hatching behavior

Time of day : Late morning through afternoon, peaking at midday

Water temperature: 50�F

Caucci and Nastasi in Hatches II say that trout feed exceptionally well on these nymphs during the hatch, and they recommend fishing nymph imitations (both deep and floating) with an upstream dead-drift. However, the duns should not be ignored, because they may ride the surface for a long time before flying away.

The hatch can be strongest on cold, dark, even snowy days.

Spinner behavior

Time of day: Midday

Habitat: Riffles

The females oviposit by repeatedly diving and dipping the tips of their abdomens into the water.

The first spinners appear a few days after the first duns, and they may persist for up to a week after the duns are done emerging.

Nymph biology

Current speed: Medium is best; slow is good; slow microhabitat in fast stretches are okay

Substrate: Gravel, detritus

Specimens of the Mayfly Species Neoleptophlebia adoptiva

1 Male Dun
1 Male Spinner
Male Neoleptophlebia adoptiva (American Blue Dun) Mayfly Spinner
Based on the pale longitudinal forewing veins (excepting the costals), dark middle terga, and genitalia (Burks '53), this specimen is P. adoptiva.

1 Streamside Picture of Neoleptophlebia adoptiva Mayflies:

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References

Species Range
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