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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.

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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Mayfly Family Siphlonuridae (Gray Drakes)

These large, slender mayflies have nymphs of the swimming type, like Isonychiidae and Metretopodidae, and they generally inhabit slow water. See Siphlonurus for details -- it is the only genus of known importance to anglers.

Where & when

In 251 records from GBIF, adults of this family have mostly been collected during June (49%), July (27%), May (11%), and August (10%).

In 489 records from GBIF, this family has been collected at elevations ranging from -30 to 11444 ft, with an average (median) of 810 ft.

Family Range


To determine whether a specimen of Ephemeroptera belongs to Siphlonuridae, use the Key to Families of Mayfly Nymphs or Key to Families of Mayfly Duns and Spinners.

Specimens of the Mayfly Family Siphlonuridae

2 Female Duns
5 Male Spinners
7 Female Spinners
10 Nymphs

3 Underwater Pictures of Siphlonuridae Mayflies:

Start a Discussion of Siphlonuridae

Mayfly Family Siphlonuridae (Gray Drakes)

Genus in Siphlonuridae: Parameletus, Siphlonisca, Siphlonurus
1 genus (Edmundsius) isn't included.
Family Range
Common Name
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