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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.
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Mayfly Species Nixe perfida

Where & when

In 8 records from GBIF, adults of this species have been collected during June (50%) and May (50%).

In 1 record from GBIF, this species has been collected at elevation of 758 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

Described in Needham et al (1935) as Heptagenia perfida
Body length: 7 mm
Wing length: 7 mm

Mesonotum brown; abdominal tergites rather deep brown with pale median and submedian streaks; genitalia of the lucidipennis type (now a synonym of Nixe lucidipennis) (see fig. 96).

Eyes pale bluish white in living insect. Head yellowish tinged with ruddy; below each lateral ocellus near the margin of the eye is a round black spot. Thoracic notum brown; anterior sutures tinged with ruddy; scutellum paler. Pleura and sternum light yellow, pleura with faint ruddy shading at bases of legs. Fore legs light yellow at base; femora pale at extreme base, otherwise deep reddish brown; tibia smoky yellow with a black spot apically; tarsi smoky. Middle and hind legs pale yellowish; femora with ruddy tinges, tibiae with faint reddish streaks at base. Wings hyaline; venation pale, veins fine; costal cross veins indistinct except those of the apical area, which are 12-13 in number, simple and straight.

Abdominal tergites rather deep brown, seeming to be tinged with reddish in certain lights. A narrow pale mid-dorsal line and lunate submedian streaks on each tergite. The lateral margin of the dark area is somewhat oblique on each segment, leaving a pale postero-lateral triangle on each. Sternites pale yellowish. Tails pale, the basal joinings narrowly reddish brown. Third forceps joint much longer than the distal one, these two together fully as long as the second. Apical margin of forceps base distinctly emarginate in the median area, with a rather prominent blunt spine-like projection of each side. Penes with a rounded apical lobe as well as a lateral one; two pairs of median spines, and a lateral spine on each side. Evidently allied to H. inconspicua (now a synonym of Afghanurus inconspicua). This species is larger than H. rusticalis (now a synonym of Nixe rusticalis) or H. inconspicua, to which it is evidently allied. Differs in details of structure of penes from H. horrida (now a synonym of Nixe horrida), its closest ally; also from H. lucidipennis (now a synonym of Nixe lucidipennis).

Start a Discussion of Nixe perfida


  • Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.

Mayfly Species Nixe perfida

Species Range
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