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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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Stonefly Species Isoperla adunca (Yellow Sallies)

Species Range


Source: The Isoperla Of California (Plecoptera: Perlodidae); Larval Descriptions And A Key To 17 Western Nearctic Species

Diagnosis. The lacinia of male Isoperla adunca larvae are distinctive in that the entire submarginal row (A + B) is continuous from the base of the apical tooth continuing to almost the inner lacinia margin (Figs. 4 g-h). Larvae lack distinct pigment patterns, especially longitudinal abdominal stripes. The lacinia of immature larvae are also distinct and resemble mature larvae, except that submarginal row (A + B) setae are more widely spaced.

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: The Isoperla Of California (Plecoptera: Perlodidae); Larval Descriptions And A Key To 17 Western Nearctic Species

Male larva. Body length of mature larva 9 – 10 mm. Dorsum of head mostly dark with fine dark clothing setae, anterior frontoclypeus margin unpigmented; light M shaped pattern anterior to median ocellus present but poorly defined, not connected to light frontoclypeus area, median longitudinal pigment band short, nearly square, lateral thin arms indistinct, directed posterolaterally and extending to antennal bases; posterior ocelli with completely enclosed small light areas along outer lateral margins; interocellar area mostly dark, usually a small unpigmented central area completely enclosed by dark pigment; occiput with irregular spinulae band extending from below eye to near median epicranial suture, partially to completely enclosed by indistinct dark pigment (Fig. 4 a). Lacinia bidentate, total length 653 – 919 µm (Fig. 2 b, 4 e- h, Tables 2 - 4); submarginal row (A + B) with 8 – 11 setae, groups A-B continuous below subapical tooth (SAT) inner margin (Figs. 4 g-h); 3 – 5 submarginal (A) setae and 4 – 6 (B) setae in a row without gap between setae until past SAT inner margin, row extending from base of apical tooth (AT) to nearly lacinia lateral margin, the last 3 – 4 setae becoming widely spaced, plus 1 thin marginal seta (TMS) adjacent to AT inner margin, sometimes obstructed from view by apical tooth, first submarginal seta or broken, and 1 dorsal seta (DS) located below subapical tooth inner margin, partially obstructed from view by first few submarginal setae (Fig. 4 h); 10 – 13 marginal setae (C) initially long-stout and widely spaced, last few shorter, variably spaced and occasionally borne from dorsal surface (Figs. 4 e, 4 g); 12 – 27 ventral surface setae (D) scattered below submarginal and marginal setae, ending posteriorly at approximately ¾ the inner lacinia margin length, occasionally a few setae below submarginal row striated (Fig. 4 f); dorsal surface setae (DSS) usually absent, sometimes last few marginal setae (C) form a short dorsal row (Fig. 4 f – arrow); 15 – 20 minute scale-like spinulae rarely present on and along ventral inner-lateral margin in basal half. Galea with 12 – 19 setae in sparse ventral row, apex with 2 – 3 setae. Maxillary Palp segments 2 – 3 with curved, apically pointed setae. Pronotum with indistinct and variable pigment pattern, median light area absent and fine dark clothing setae; discs occasionally with slightly darker comma shaped areas near lateral margins, lateral margins with broad light bands (Fig. 4 b). Mesonotum and metanotum with indistinct pigment pattern and fine dark clothing setae (Fig. 4 c). Legs with numerous fine light brown clothing setae and scattered erect spines on outer surface of femora, erect spines longest and concentrated along dorsal surfaces; fine silky setae sparse on dorsal surface of femora, numerous and continuous on tibia (Fig. 20 b); tibia with faint transverse bands near proximal end. Abdominal terga without distinct longitudinal dark stripes; numerous fine light clothing setae and erect spines scattered dorsally; posterior margin with scattered long and numerous short spines in a concentrated row (Fig. 4 d).

Source: The Isoperla Of California (Plecoptera: Perlodidae); Updated Male Descriptions And Adult Keys For 18 Western Nearctic Species

Male. Aedeagus: sclerotized posterior process present; body with one posterobasal and one posteromedian lobe, dorsomedian apex with a pair of rounded lobes, and one anterior lobe (Fig. 2 a); sclerotized process length approximately 0.25 mm, recurved and rod-like, located below posterior lobes (Fig. 2 a), and apex clavate in posterior and lateral views (Figs. 2 a-b). Abdominal terga 8 - 9, 9, or 9 - 10: without stout spinulae or long stout setae. Posterolateral margins of at least abdominal segment 8 with scale-like setae clustered in brushes of several setae. Paraprocts: curved dorsally, length if straightened subequal to first and second cercal segments, tapering gradually to blunt apices (Fig. 2 c). Vesicle: pedunculate, length subequal to width, constricted near base with curved lateral margins, wider and rounded at apex (Fig. 2 d).

Start a Discussion of Isoperla adunca

Stonefly Species Isoperla adunca (Yellow Sallies)

Species Range
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