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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Dorsal view of a Limnephilidae (Giant Sedges) Caddisfly Larva from the Yakima River in Washington
This specimen resembled several others of around the same size and perhaps the same species, which were pretty common in my February sample from the upper Yakima. Unfortunately, I misplaced the specimen before I could get it under a microscope for a definitive ID.
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 Ephemeridae (Hexes and Big Drakes)

Several great superhatches come from this family. The Green, Yellow, and Brown Drakes all belong to the Ephemera genus. Hexagenia and Litobrancha contain the largest mayflies in North America and present legendary fly fishing opportunities, especially the famed "Hex hatch" of Hexagenia limbata.

Where & when

In 412 records from GBIF, adults of this family have mostly been collected during June (36%), July (27%), August (16%), May (10%), and September (7%).

In 157 records from GBIF, this family has been collected at elevations ranging from 3 to 11102 ft, with an average (median) of 2782 ft.

Family Range

Nymph biology

Nymphs of this family are nocturnal and their pale bodies sensitive to the sunlight. They build U-shaped burrows less than six inches into the stream bottom, where they feed on microorganisms in the fertile sediment. They come out of these burrows to molt up to 30 times throughout their development. They require sediment of a particular density, soft enough for them to dig burrows but hard enough that the burrows don't collapse.

It common in this family for nymphs to live 2-3 years before emerging. This is very unusual among mayflies.


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

Specimens of the Mayfly Family Ephemeridae

6 Male Duns
11 Female Duns
10 Male Spinners
4 Female Spinners
15 Nymphs

7 Streamside Pictures of Ephemeridae Mayflies:

3 Underwater Pictures of Ephemeridae Mayflies:

Discussions of Ephemeridae

Hex hatch water temperature range?
4 replies
Posted by NEMatt on May 23, 2014 in the species Hexagenia limbata
Last reply on Jul 5, 2016 by Bombillo

New to the site - love it. I was wondering if there was a suggested range of water temperature at which the Hex likes to hatch.

What is the big DEAL about the HEX?
21 replies
Posted by Spinner on Jun 21, 2006 in the species Hexagenia limbata
Last reply on Jul 5, 2016 by Bombillo
fishing in the dark.......
stepping in holes?

I hate the dark........

I don't need the hex........

Green Drake Hatch Temp?
1 replies
Posted by NEMatt on May 23, 2014 in the species Ephemera guttulata
Last reply on May 23, 2014 by Entoman

I was looking for a water temperature range for the Green Drake hatch. Anyone know?
Mayfly larvae -wigglers preservation as bait
20 replies
Posted by Teacherprea on Jun 2, 2007 in the species Hexagenia limbata
Last reply on Apr 29, 2014 by TNEAL
I am a fly fisherman but not a "purist". A friend of mine has a place on the UP of Michigan. He just called me and said a guy told him there is a way to preserve "wigglers." They use them alot up north, those that are not fly fishermen or ladies. They are fishing perch, bluegill and crappie. He heard there is a way to "blanch" them.Drop them in hot water for a few minutes and they turn rubbery. They then will keep indefinitely. Has anyone heard of this? If so, how close to correct is the procedure I mentioned??
Thanks for anyone's help.
GD Shuck
10 replies
Posted by Martinlf on May 29, 2013 in the species Ephemera guttulata
Last reply on Jun 2, 2013 by Crepuscular
Jason's photo of a GD shuck suggests that at hatch time the backs of the nymphs may be a greyish or grey olive color. Possibly useful information, if this is an accurate surmise.

Start a Discussion of Ephemeridae


Mayfly Family Ephemeridae (Hexes and Big Drakes)

Genus in Ephemeridae: Ephemera, Hexagenia, Litobrancha
Family Range
Common Name
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