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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 Tricorythodes explicatus (Tricos)

This hatch is fairly well-known to anglers under its former name Tricorythodes minutus, which was one of the species responsible for good Trico fishing.

Taxonomic History

The former species Tricorythodes minutus was recently renamed based on taxonomists' determination that the earlier-discovered explicatus is the same species, and the earlier name took precedence despite the minor popularity of the now-invalid minutus.

Where & when

This is certianly the most important Tricorythodes species in the West, and it can be important in the East and Midwest as well. It is reported to grow as large as hook size 18 in the West only.

In 27 records from GBIF, adults of this species have mostly been collected during July (41%), September (15%), June (11%), April (11%), August (11%), and May (7%).

In 38 records from GBIF, this species has been collected at elevations ranging from 486 to 6293 ft, with an average (median) of 5210 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: 2.5-5 mm
Wing length: 3.5-7 mm

Body pitch-black; femora deep pitch brown, tibiae brownish, tarsi yellowish white; forceps base of male with a very shallow apical excavation.

Head and eyes dull black; ocelli shining milky-white, dark-ringed at base; posterior tubercles shiny. Thorax dull black; pronotum with a hourglass-shaped lateral shiny brownish-black patch. Femora of all legs deep pitch-brown; the fore tibia 2.5 mm. long, light brown; middle and hind tibiae shaded with pitch-brown, becoming yellowish-white apically; all tarsi yellowish white. Wings whitish, hyaline; venation indistinct; subcosta and radius blackish except at base. Abdomen wholly dull black, with satiny lustre. Forceps whitish; penes (see fig. 160) shiny blackish brown, base paler, and bent upward at right angles; forceps base very shallowly excavated apically. Tails whitish, the edges and joinings black.

Described as T. fallax

Body length 5 mm, wing length 6 mm

Mesonotum deep blackish brown; middle and hind femora pale reddish brown, fore tibia and tarsus white; tails smoky grey; forceps base very shallowly excavated.

Male—Head deep mahogany brown, often with a pale spot in middle of vertex; ocelli whitish, black-ringed at base; eyes black; antennae pale, the second joint brown basally, filament brownish at extreme base. Pronotum deep mahogany brown; postero-lateral corners pale whitish. Mesonotum blackish brown; antero-lateral margins and sutures anterior to scutellum pale yellowish; scutellum blackish. Pleura deep red-brown, with rather extensive pale areas below and behind the wing roots and around the leg bases. Prosternum whitish; mesosterna and metasterna pale brown in median area, remainder deep mahogany brown. Coxae and trochanters of all legs deep red-brown, with slight blackish markings. Fore femur dark red-brown, a white area on outer side near base, dorsal and ventral edges black; ‘knee’ black; tibia and tarsus wholly white except terminal tarsal joint which is pale smoky; apex of tibia narrowly black. Middle and hind femora pale reddish brown, often with whitish areas near base; ‘knees’ black; tibiae and tarsi whitish, each tibia with a smoky ventro-basal and dorso-apical dark spot. Wings hyaline, whitish; subcosta and radius purplish black, other longitudinal veins finer but of same dark color.

Abdomen dark reddish brown. Tergites 1, 2, 8 and 9 almost wholly black; tergites 3-7 black in dorsal area, brown Iaterally, with variable amount of blackish shading; tergite 10 reddish brown. Posterior margins of all tergites and sternites narrowly pale, giving abdomen an annulate appearance. Heavy black markings, somewhat irregular, along spiracular area of basal and middle tergites. Hyaline, oblique, short dashes on each side of sternites next to pleural fold; mid-ventral area faintly greyish black; a pair of small hyaline dots anterior to center of each sternite, one on each side of median line. Sternite 9 brown at base and apical margin of forceps base, remainder white. Forceps white basally and at tip, second joint smoky; penes as in Tricorythodes explicatus. Forceps base very shallowly excavated apically, as in explicatus. Tails rather deep smoky grey, somewhat paler apically; joinings hyaline, base and apex of each joint darker.

Described as T. minutus

Body length 2.5 mm, wing length 3.5mm

A small reddish brown species, quite similar in general appearance to T. fallax (now a synonym of Tricorythodus explicatus); forceps base rather shallowly excavated; middle and hind legs wholly red-brown.

Male—Head quite bright reddish on vertex; posterior margin blackish; antennae pale reddish; eyes black; posterior ocelli whitish, black-ringed at base. Thorax deep red-brown; pronotum shaded heavily with blackish in median and lateral areas. Mesonotum deeper in color; a narrow pale yellowish streak on sutures anterior and laterad of scutellum; pale areas on pleura limited to regions below and anterior to wing roots and around leg bases. Femora of all legs, and tibiae and tarsi of middle and hind legs, light reddish brown; fore tibia and tarsus whitish; ‘knee’ of fore leg darker red-brown. Wings whitish, hyaline; venation pale except for purplish subcosta and radius.

Abdomen reddish brown. Tergites 1, 2, 8 and 9 largely blackish; intermediate tergites reddish brown laterally, with a narrow red-brown median line, on each side of which is a heavy blackish shading, leaving the posterior margins narrowly pale. Sternites apparently unmarked except for a large black lateral triangle on each side of sternite 9. Tails pale smoky at base, pale distally; joinings and lateral margins narrowly blackish, in basal portion. Forceps base reddish brown, darker on apical margin, which is quite shallowly excavated. Penes light reddish; forceps very pale smoky.

Start a Discussion of Tricorythodes explicatus


Mayfly Species Tricorythodes explicatus (Tricos)

Species Range
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