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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 Teloganopsis deficiens (Little black Quills)

Anglers in western Wisconsin, where these little flies hatch in good numbers on summer rivers, have termed them "Darth Vaders" because of the very dark color of their wings.

Until recently, this species was known as Serratella deficiens.

Where & when

Time of year : June and July

Most writers say this species emerges in June and July, but Caucci and Nastasi in Hatches II report that it is important in the Catskills in the late summer and fall. The others might be referring to hatches in the Midwest, where the species is also prolific, or there may be some confusion between species.

In 13 records from GBIF, adults of this species have been collected during June (46%), July (23%), December (15%), February (8%), and August (8%).

In 19 records from GBIF, this species has been collected at elevations ranging from 299 to 2559 ft, with an average (median) of 1982 ft.

Species Range

Hatching behavior

Time of day : Late morning.

The tiny duns take a while to break through the surface film, and then they linger on the surface before flying off. Despite their small size they can provide excellent fishing where they are abundant.

The angling literature says they hatch in late morning, and anglers familiar with the hatch confirm this, but they also report afternoon and evening hatches.

Spinner behavior

These spinner falls are unimportant.

Nymph biology

Current speed: Slow to medium

Substrate: They do especially well in weedy streams.

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 Ephemerella deficiens
Body length: 5 mm
Wing length: 5 mm

A member of the serrata (now a synonym of Serratella serrata) group; distinguished fromE. sordida (now a synonym of Serratella serrata), in the male imago, by the deep blackish brown abdominal tergites, the prominent dark apical spot on the middle and hind femora, and the blackish apical portion of the penes. Head and thorax blackish brown. Eyes reddish brown, antennae brown. Vertex of head in female deep wine-red. Pronotum brown; mesothorax and metathorax brown, likewise the pleura, all with blackish markings. Sternum brown. Coxae brown; legs nearly white, the femora with a prominent dark brown spot apically, especially prominent on the middle and hind legs. Wings hyaline, veins pale; brown shading at base of wings. Abdominal tergites deep blackish brown; sternites paler. Tails pale, the joinings narrowly but distinctly purplish brown. Forceps pale; penes whitish basally, blackish apically (see fig. 156).


Described in Needham et al (1935) as Ephemerella deficiens

Nymph blackish (rarely dull brown), usually with a pale median thoracic stripe dorsally. Head and thorax smooth; maxillary palp entirely wanting; no dorsal abdominal spines. Lateral extensions of the abdominal segments and postero-lateral spines only moderately developed; tips of the spines whitish. Gills present on segments 3-7. Each claw with 8-9 denticles. Tails yellowish brown; a wide dark median band crosses the two outer ones; at each joining, a circle of prominent spines. Femora dark brown, tibiae and tarsi yellowish with wide brown bands. Two pale spots laterally on each side of the pronotum.

Specimens of the Mayfly Species Teloganopsis deficiens

1 Nymph

Start a Discussion of Teloganopsis deficiens


Mayfly Species Teloganopsis deficiens (Little black Quills)

Species Range
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