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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 Epeorus permagnus

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 Ironopsis permagnus
Body length: 13-15 mm
Wing length: 17-19 mm

Larger than I. grandis (now a synonym for Epeorus grandis), with darker mesonotum; spining on ventral surface of each division of penes much more extensive.

Head deep brown; no dark band on frontal margin; shaded with black around bases of antennae and sides of median carina. Thorax almost unicolorous black-brown. A single short black streak anterior to wing roots. Area anterior to wing roots often yellowish. Fore femur black-brown, paler at extreme base; tibia and tarsus blackish red-brown. Middle and hind legs light red-brown; femora shaded extensively with blackish; tarsi slightly deeper in color than tibiae. Coxae and trochanters of all legs black-tipped. Wings hyaline. Costa, subcosta and radius yellowish at extreme base, costa yellowish also in apical third; remainder of these veins thickened, dark reddish to purplish brown. Other longitudinal veins finer, paler red-brown; cross veins still finer, yellowish to light red-brown. 11 to 12 basal costal cross veins, very faint; humeral cross vein pale.

Abdominal tergites largely yellowish to olive brown. Large black-brown patches occupy tergites 2 and 3, leaving margins and median line pale. Tergites 4 and 5 with more restricted dark central areas, the margins irregular; lateral and antero-lateral margins pale, mid-dorsal line obscured. Tergites 6-8 with black-brown median triangle based on anterior margin, its apex extending backward along median line about 3/4 the length of each tergite, leaving large pale postero-lateral triangles, with a small rounded brown mark in each. Tergites 9 and 10 more reddish brown; anterior margins narrowly black; black spot laterally on 9; median line and median area of posterior margin of 10 blackish. Sternites olive brown; basal ones shaded with red-brown. A rounded smoky spot near antero-lateral angle of each intermediate sternite, the two spots on each sternite connected by a smoky transverse band. Sternite 8 shaded with red-brown; 9 deeper brown, with greyish posterior and postero-lateral margins. Pleural fold greyish on all segments. Tails deep red-brown, almost black-brown at base; joinings narrowly paler. Forceps deep red-brown, paler apically. Penes light red-brown, with many small spines on ventral surface of each division (see fig. 111).

Start a Discussion of Epeorus permagnus


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

Mayfly Species Epeorus permagnus

Species Range
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