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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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This topic is about the Mayfly Family Leptophlebiidae

The champions of this family are Leptophlebia and Paraleptophlebia, along with the relatively newly-defined genus Neoleptophlebia containing several important species that were once in Paraleptophlebia. The large mayflies of Leptophlebia are on the water sporadically for a long time. The Paraleptophlebia and Neoleptophlebia flies are smaller but come in much more concentrated numbers.

Leptophlebiidae also contains several genera and species which are never mentioned in fly-fishing literature, either because they are too rare or because they require water too warm for trout.

Example specimens

Prescott, AZ

Posts: 1
JasonM on Mar 6, 2010March 6th, 2010, 7:18 pm EST
I live in Arizona and I have a question...

Over the past several years I have witnessed a spectacular emergence of mayflies on a stream I frequent in the Mogollon Rim area of Arizona. The stream is a tributary to the Little Colorado River drainage.

The adults seem to emerge on exposed midstream rocks of along the shoreline. The duns can be very dense, sometimes every rock along shore has one drying its wings beforetaking flight They are a dark greyish brown bodied, dark grey winged adult, I have named them MOCHA DUNS for lack of knowledge of their true identity. Three tails on the adult as well. They are pretty big....a big size 14 to 16. I have captured several specimens as larvae that I believe are the same species as the ones I have observed as adults. The larvae have prominent gills. 3 long split tails, similar size and color, hign densities along shore and in the shallows, etc. I'm 90% sure that they are Leptophlebiidae. But I don't know the species, yet.

The trout don't seem to key in on the adults...since they emerge on land...but I have experienced some incredible fishing during very windy days while the hatch is on. The nymphs appear to have trouble holding on to the substrates they are trying to emerge on. I have witessed several swimming to a streamside cobble, grasping the rock for a moment, only to be swepped back into the water by small, lapping waves being caused by the wind. They try repeatedly but seem to get exhausted pretty quickly. They must be easy picking for fish cruising along the bank, as I have great success fishing imitations along the shore with short twitches. I have rarely seen duns on the surface of the stream, even on the windiest of days. They seem to emerge late morning to early afternoon.

CAN ANYBODY SUGGEST WHAT SPECIES THIS MAYBE. I don't have a scope or any literature anymore. I have experience with ID'ing but not lately

Any help would be appreciated by this inquisitive angler. Thanks

Jason Mszaros
The Drag Free School of Fly Fishing
Taxon's profile picture
Site Editor
Plano, TX

Posts: 1311
Taxon on Mar 6, 2010March 6th, 2010, 7:45 pm EST

What month of the year does this emergence seem to peak?

If it's some time between mid-June and mid-July, my guess would be Paraleptophlebia memorialis.

Here is a detailed description:

Family: Leptophlebiidae
Scientific name: Paraleptophlebia memorialis

Previously know as: Leptophlebia memorialis, Leptophlebia pallipes (in part), Paraleptophlebia pallipes
Common name: Mahogany Dun, etc.
Locality: W
CAN Regions: NW
MEX Regions: SW
USA Regions: NW, SW
Cent. Amer. Countries:
CAN Provinces: AB, BC.
MEX States: BN.
USA States: AZ, CA, CO, ID, NM, OR, SD, UT, WA
Emergence (begin) date: mid-Jun
Emergence (end) date: early-Aug
Emergence time of day: afternoon
Spinner fall time of day:

Nymph minimum length: 6 mm.
Nymph maximum length: 7 mm.
Nymph identification keys: gill fork 1/3 from base; abdominal spines on segment 8 & 9; tergites dark, each w/three light dots, a medium-sized one on center-line, and a small-sized one forward on each side of center-line
Nymph body description:
Nymph legs:
Nymph gills: gill/filament length ratio (1:3), trachael branching: (absent)
Nymph tusks: absent
Nymph tails: 3,

Dun minimum length: 6 mm.
Dun maximum length: 8 mm.
Dun identification keys:
Dun body description: brown to dark reddish brown
Dun wings: medium gray, hind wings w/o costal angulation
Dun legs: brown
Dun tails: 3, light to dark brown

Spinner minimum length: 7 mm.
Spinner maximum length: 7 mm.
Spinner identification keys: male claspers w/3 joints
Spinner body description: abdomen whitish
Spinner wings: hyaline, fore wing with attached intercalaries, hind wing w/o costal angulation
Spinner legs:
Spinner tails: 3,

Best regards,
Roger Rohrbeck

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