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.

Stream photos

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Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Mayfly Species Paraleptophlebia packii (Mahogany Dun)

This large western species is common in places. It is one of the few that has tusks and substitutes for the more common tusked Paraleptophlebia bicornuta in some locales, particularly the central Rockies in parts of Colorado, Utah, and Wyoming where they have been documented. Telling the tusked species apart is very difficult and even entomological texts are largely ambiguous on the characters that differentiate the nymphs. Angling texts relying on gill morphology, terga pattern, and tusk shape are dubious at best. For now, the angler's best bet is to rely somewhat on documented distribution.

Where & when

Time of year : Fall

Species Range

source

Hatching behavior

Time of day : Late morning through evening

Egg-Laying behavior

Ernest Schwiebert reports in Matching the Hatch that the spinners return four days after emerging as duns.

Nymph biology

Current speed: Slow water

Physical description

Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.

Male Spinner

Described in Needham et al (1935)

Body length: 9 mm
Wing length: 12 mm

This is our largest species of the genus. The sexes are alike in color, all brown, deepening to shining black on top of thorax and at both ends of abdomen, paler on appendages. Wings subhyaline with brown veins, and with a brown tint in the membrane at the roots. Costal cross veins numerous but weak as far as the stigmatic area where they are crowded; their tips strongly curved outward and often forked. Sometimes they anastomose forming a few small cells in an outer series next the costa. Vein Cu₂ unattached at base. The forceps has a rounded basal lobe-like dilatation. The penes are separated by a broad U-shaped notch as wide as deep; the terminal orifice is guarded by a rounded inner lobe and an outer triangular tooth. The reflexed spur is short, lance-like or bladelike, and acute at the apex.

Female Spinner

Described in Needham et al (1935)

Body length: 9 mm
Wing length: 12 mm

The subanal plate in the female is divided into two elongate triangular lobes that extend rearward beyond the abdomen more than the length of the 9th segment (see fig. 134).

Start a Discussion of Paraleptophlebia packii

References

Caucci, Al and Nastasi, Bob. 2004. Hatches II. The Lyons Press.
Knopp, Malcolm and Robert Cormier. 1997. Mayflies: An Angler's Study of Trout Water Ephemeroptera . The Lyons Press.
Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.
Schwiebert, Ernest G. 1955. Matching the Hatch. MacMillan Publishing Company.