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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.

Dorsal view of a Setvena wahkeena (Perlodidae) (Wahkeena Springfly) Stonefly Nymph from Mystery Creek #199 in Washington
As far as I can tell, this species has only previously been reported from one site in Oregon along the Columbia gorge. However, the key characteristics are fairly unmistakable in all except for one minor detail:
— 4 small yellow spots on frons visible in photos
— Narrow occipital spinule row curves forward (but doesn’t quite meet on stem of ecdysial suture, as it's supposed to in this species)
— Short spinules on anterior margin of front legs
— Short rposterior row of blunt spinules on abdominal tergae, rather than elongated spinules dorsally
I caught several of these mature nymphs in the fishless, tiny headwaters of a creek high in the Wenatchee Mountains.
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 Species Neoleptophlebia mollis (Jenny Spinners)

This species often emerges together with Paraleptophlebia strigula and Paraleptophlebia guttata, and the combined effect can be a good fishable hatch. The latter two are much less famous than mollis, but Knopp and Cormier say they are more reliable.

Where & when

Time of year : Late May through August; best in June

This species begins to emerge soon after Paraleptophlebia adoptiva has finished.

In 11 records from GBIF, adults of this species have been collected during June (45%), July (45%), and May (9%).

In 4 records from GBIF, this species has been collected at elevations of 3, 69, 240, and 643 ft.

Species Range

Hatching behavior

Time of day : Late morning to midday

The duns ride the surface for a long time before flying away. The Leonards report in Mayflies of Michigan Trout Streams that trout feed heavily on Paraleptophlebia mollis duns.

Spinner behavior

Time of day: Late afternoon

The male spinners have a unique look: most of their abdominal segments are white.

Nymph biology

Current speed: Slow

Environmental tolerance: Tolerant of warm 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) as Paraleptophlebia mollis
Body length: 8 mm
Wing length: 8 mm

This is a white-winged, white-legged, white-tailed species with dark brown thorax and brown tipped white abdomen. Head, thorax, and basal segment of the abdomen brown, darker above and beneath, with paler sutures at the sides. All appendages white. Wings white with whitish veins and with scarcely any darkening of the stigmatic area. Costal cross veins almost undiscoverable except in the stigmatic area where they are rather crowded, strongly aslant, sinuous, and sometimes forked. Segments 2 to 7 of the abdomen entirely translucent white, with no markings on either ganglia or spiracles. Segment 8 is pale brown, 9 and 10 are somewhat darker brown. Forceps and tails white. Penes pale brown, separated by a narrow cleft; each tip bears externally a thin, flat, triangular lobe that terminates laterally in a sharp, upcurving thorn-like point (see fig. 133).

Specimens of the Mayfly Species Neoleptophlebia mollis

1 Male Dun

Start a Discussion of Neoleptophlebia mollis


Mayfly Species Neoleptophlebia mollis (Jenny Spinners)

Species Range
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