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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.
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 Serratella serrata (Little Sooty Olives)

This locally important species is rarely mentioned in fly fishing literature, and what little information is given is identical to that for Teloganopsis deficiens. Knopp and Cormier say both species can produce good hatches.

Where & when

In 16 records from GBIF, adults of this species have been collected during July (50%), August (31%), and June (19%).

In 3 records from GBIF, this species has been collected at elevations of 1713, 1901, and 2001 ft.

Species Range

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: 5 mm
Wing length: 6 mm

A brightly colored species; eyes of male orange-red, body brighter brown than E. deficiens (now a synonym of Teloganopsis deficiens) or E. sordida (now a synonym of Serratella serrata).

Eyes of living male orange-red; head brown, lighter in front. Antennae pale brown. Thorax yellowish dorsally, shaded with brown. Posterior margin of mesonotum margined with brown; pleura with brown shading. Sternum pale with median and lateral dark brown areas. Legs pale; femora banded with brown apically. Wings hyaline, tinged with brown at the base; veins pale. Abdomen brown dorsally, pale ventrally, with no curved row of dark dots such as occur in E. serratoides (now a synonym of Serratella serratoides). Tails pale, the basal joinings brown.

Described as E. sorida

Body length 5 mm, wing length 6 mm

A species of the serrata group (now a synonym of Serratella serrata); male imago duller in color than E. deficiens (now a synonym of Teloganopsis deficiens) with tails unmarked.

Eyes deep blackish brown. Head and thorax blackish brown; pleura with lighter brown shading; lateral extensions of mesosternum paler. Head of female “light ruddy ochreous” (McD.). Legs pale yellowish, fore legs somewhat tinged with smoky. Middle and hind femora with indications of brown spots apically. Fore tibia twice the length of the femur, and slightly longer than the entire tarsus. Wings hyaline, all veins pale. Abdominal tergites dull blackish, the three posterior segments brownish. Sternites paler, rather smoky, becoming opaque and pale grey posteriorly. Genitalia and tails whitish; tails unmarked. Penes as in fig. 156.


Head of nymph somewhat roughened on the vertex, but with no distinct occipital tubercles. Feeble wart-like processes on each side of the median line of the prothorax. Dorsal spines represented by wart-like spicule-bearing processes. Gills present on tergites 3-7. Postero-lateral spines become increasingly acuminate to rearward, that on the 9th segment extending beyond the end of segment 10. Lateral margins of abdominal segments bear conspicuous spinules. Tails pale, with a median band of dark brown. Each claw with 3-4 denticles. General color brown; legs and venter paler; tergites 5-6 with brown pencilings. Abdominal sternites marked with a lateral row of dark dashes, but with no curved row of dark dots between these rows.

Described as E. sorida

Head and thorax of nymph smooth, but quite hairy. Dorsal spines represented by the usual wart-like processes. Postero-lateral spines longer than in any other species of this group; the spine on segment 9 extends well beyond the 10th segment. Gills on segments 3-7. Legs hairy, the anterior margin of the femora with a few spinules. General color pale yellowish brown to olive; no ventral markings. Femora usually dark with pale bands; tibiae pale with a wide median dark band; tarsi dark basally. Tails pale, without dark markings.

Start a Discussion of Serratella serrata


Mayfly Species Serratella serrata (Little Sooty Olives)

Species Range
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