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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.

Lateral view of a Onocosmoecus (Limnephilidae) (Great Late-Summer Sedge) Caddisfly Larva from the Yakima River in Washington
This specimen keys pretty easily to Onocosmoecus, and it closely resembles a specimen from Alaska which caddis expert Dave Ruiter recognized as this genus. As with that specimen, the only species in the genus documented in this area is Onocosmoecus unicolor, but Dave suggested for that specimen that there might be multiple not-yet-distinguished species under the unicolor umbrella and it would be best to stick with the genus-level ID. I'm doing the same for this one.
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 mosegus (Tricos)

Where & when

In 4 records from GBIF, adults of this species have been collected during July (75%) and September (25%).

In 2 records from GBIF, this species has been collected at elevations of 3 and 771 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.

Source: Life stage descriptions, taxonomic notes, and new records for the mayfly family Leptohyphidae (Ephemeroptera)

Larva: Body length 4.5 – 5.5 mm; caudal filaments 2.5 – 3.5 mm. Head: Compound eyes remote, widely separated; ocelli clear. Antennae approximately 2 x length of head capsule. Mouthparts: Labrum (Fig. 19) dorsally with long, fine simple setae along lateral margin; row of elongate, branched setae recessed from anterior margin; ventrally with vertical row of simple, fine setae near mid­line, and row of short, branched setae along anterior margin. Right mandible (Fig. 20) with outer incisors three-lobed; inner incisor two-­lobed; prostheca and molar region as in Fig. 20; scattered setae on dorsal surface. Left mandible (Fig. 21) with outer incisors four-­lobed, mostly fused; inner incisor with two denticles; prostheca arising at base of inner incisor, appearing fused with side of outer incisor; molar region as in Fig. 21; scattered setae on dorsal surface. Hypopharynx with long, fine simple setae on anterior surface (Fig. 22); inner basal edge of superlinguae with row of setae. Maxilla (Fig. 23) with three-­segmented palp and short, terminal setae; apex of galealacinia with two large fused apical spines, row of heavy setae. Labium (Fig. 24) with moderately ­expanded mentum with numerous long, simple setae along outer margins and ventrally; glossae and paraglossae subequal in length with smooth margins; glossae with small fine, simple setae; paraglossae with numerous long, simple setae; notch between glossae slightly deeper and more rounded than notches between glossae and paraglossae; labial palp three­-segmented with long, simple setae. Thorax: Scattered small hairs and setae present. Dorsal surface of forefemur with median transverse row of long setae, inner margin with smaller setae basally and outer margin with row of long setae apically (Fig. 25). Tarsal claws (Fig. 26) with single row of uniform, small flattened denticles numbering 10 – 12. Meso­femora and metafemora with few, scattered setae on dorsal surface not forming a distinct row as in forefemur; meso­claws and metaclaws with approximately 10 and 12 denticles, respectively; denticles sometimes flattened and appear as a single structure. Abdomen: Scattered hair-like setae present on terga. Dorsal lamella of gill 2 (operculate gill) subtriangular, brownish-­yellow with scattered patches of black shading (Fig. 27); outer margin with longitudinal ridge and scattered small setae along edge of ridge; numerous long and short setae along margin of gill. Cerci with row of setae at each annulation.

Start a Discussion of Tricorythodes mosegus

Mayfly Species Tricorythodes mosegus (Tricos)

Species Range
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