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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 Skwala (Perlodidae) (Large Springfly) Stonefly Nymph from the Yakima River in Washington
This Skwala nymph still has a couple months left to go before hatching, but it's still a good representative of its species, which was extremely abundant in my sample for a stonefly of this size. It's obvious why the Yakima is known for its Skwala hatch.
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 Heptagenia elegantula (Pale Evening Duns)

The spinner falls of this elegant species can be quite important to anglers across the West. Recent revisions have synonymized the Midwestern species Heptagenia diabasia that may be of some local importance.

Where & when

Time of year : June and Juuly

Preferred waters: Large rivers

Altitude: Below 6,000 feet

The hatch dates given for Heptagenia elegantula in Selective Trout are August 5th to September 25th. This conflicts with the June and July dates claimed by two other authors.

In 36 records from GBIF, adults of this species have mostly been collected during June (36%), July (33%), August (19%), and May (6%).

In 78 records from GBIF, this species has been collected at elevations ranging from 502 to 11001 ft, with an average (median) of 4905 ft.

Species Range

Hatching behavior

Time of day : Late morning for less than an hour

Water temperature: Above 50°F

According to Fred Arbona in Mayflies, the Angler, and the Trout, the duns of this species emerge and fly off the water so quickly that they aren't important to imitate.

Spinner behavior

Spinner falls give the best fishing offered by elegantla. They follow the typical Heptagenia spinner behavior.

Nymph biology

Current speed: Slow to moderate

Substrate: Fine gravel, maybe sand or silt

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

Body length: 9-10 mm
Wing length: 9-12 mm

A yellowish species; reddish brown dorsal stripe on mesonotum, black markings on pleura above coxae; genitalia as in fig. 94.

Head pale yellowish; a reddish spot on frontal carina, and red shading on vertex between eyes and ocelli. Thoracic notum pale yellowish; a median reddish brown stripe on mesonotum, and pinkish area anterior to scutellum. Pleura and sternum likewise yellowish; pinkish areas on pleura below base of each wing; a black streak above base of middle and hind coxae, and a black spot posterior to hind coxae. Fore leg light bronzy brown; femur indistinctly banded at middle with light reddish brown, red-brown also at apex; apex of tibia, distal tarsal joint and tarsal joinings, also claws, dull reddish to blackish brown. Middle and hind legs yellowish amber; no median femoral band; tip of tibia not darkened. Basal joint of fore tarsus about 1/6 the length of the second joint. Wings hyaline. Costal margin of fore wing may be tinged with pale lemon yellow, with greenish or bistre-grey. Subcosta and radius yellowish amber in basal half; other longitudinal veins fine, pitch brown to black. Humeral cross veins thickened posteriorly, blackish. Cross veins dark; those in costal space thicker than others, black; a well-marked black bulla.

Abdominal segments pale; 2-7 semi-hyaline, 8-10 opaque. Posterior margins of tergites 2-7 smoky greyish or brownish; tergites 8-10 tinged with pink. Sternites pale yellowish. Tails pale yellowish, joinings dark brown. Genitalia distinctive.

Specimens of the Mayfly Species Heptagenia elegantula

1 Nymph

Start a Discussion of Heptagenia elegantula


Mayfly Species Heptagenia elegantula (Pale Evening Duns)

Species Range
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