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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.

Case view of a Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
It's only barely visible in one of my pictures, but I confirmed under the microscope that this one has a prosternal horn and the antennae are mid-way between the eyes and front of the head capsule.

I'm calling this one Pycnopsyche, but it's a bit perplexing. It seems to key definitively to at least Couplet 8 of the Key to Genera of Limnephilidae Larvae. That narrows it down to three genera, and the case seems wrong for the other two. The case looks right for Pycnopsyche, and it fits one of the key characteristics: "Abdominal sternum II without chloride epithelium and abdominal segment IX with only single seta on each side of dorsal sclerite." However, the characteristic "metanotal sa1 sclerites not fused, although often contiguous" does not seem to fit well. Those sclerites sure look fused to me, although I can make out a thin groove in the touching halves in the anterior half under the microscope. Perhaps this is a regional variation.

The only species of Pycnopsyche documented in Washington state is Pycnopsyche guttifera, and the colors and markings around the head of this specimen seem to match very well a specimen of that species from Massachusetts on Bugguide. So I am placing it in that species for now.

Whatever species this is, I photographed another specimen of seemingly the same species from the same spot a couple months later.
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 Osobenus yakimae (Yakima Springflies)

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 Nymph

Described in Jewett (1955) as Isogenus yakimae
Body length: 12 mm

Antennal segments about 44, basal segment large, third about twice length of second and half as large as first. Cercal segments about 25; long, erect swimming hairs dorsally on segments. Submental gills absent.

General color yellow with brown markings on head, thorax, and dorsum of abdomen. Ocellar area on head dark brown as in figure 5, this colored area extending forward to clypeus on either side of median ocellus; yellow areas behind rear ocelli and anterior to median ocellus; clypeus yellow. Prothorax brown except for large central yellow area; mesothorax and metathorax brown except for irregular yellow areas centrally. Dorsum of abdomen brown with narrow median yellow stripe; sides and venter of thorax yellow. Antennae, legs, and cerci mostly yellow. Mesosternal ridge pattern similar to that illustrated by Ricker (1952, page 65, figure 36J) for adult except that arms of Y reach
posterior corners of furcal pits.

Maxilla with major and minor tooth, figure 5A; one or two small bristles at base of minor tooth. Tip of maxilla without tufted knob. Mandibles with several teeth, fringe of hairs in patch below teeth on inner margin. Labium, figure 5B, with tips of paraglossae slightly knobbed. Mature male nymph with genitalia partly discernible, figure 5C.

In possessing a dorsal abdominal stripe this nymph closely resembles species in the genus Isoperla.

Source: Descriptions Of The Adult Male And Female Genitalia Of The Genus Osobenus Ricker (Plecoptera: Perlodidae)

Descriptions: Male. Pale yellowish brown in color, head with obscure brownish marking, pronotum with a broad yellow stripe (Fig. 1). Tenth tergum deeply cleft, hemitergal lobes elongate, narrowly rounded at apex, bearing ribbed peg-like sensilla basiconica and trichoid sensilla (Figs. 2 – 3). Lateral stylets absent. Epiproct, large, bulbous, triangular in shape (Figs. 4, 5, 10 – 13). Ventral sclerite brown, strap-like, terminating in downturned spine in repose (Figs. 4, 6 – 8, 12); dorsal sclerite brown, terminating between two external patches of stout spinulae and continuing internally to form a coiled sac (Figs. 6, 10 – 12, 14); laterally covered by dense hairs (Figs. 4 – 7). Epiproct with a wide opening on dorsal surface located behind external paired patches of 6 - 7 spines each (Figs. 6 – 9) arising from two longitudinal membranous swellings; opening internally connected to a coiled sac with two basolateral patches of internal spines (Fig. 15).

Female. Subgenital plate parabolic (Fig. 16).

Egg. Typical of the Diploperlini, oval shape, medially with raised ridge, cross section semicircular (Fig. 17). Chorion with visor-like extension covering collar (Fig. 17), chorion with dense punctations, visor coarsely punctate (Fig. 17).

Specimens of the Stonefly Species Osobenus yakimae

1 Nymph

Start a Discussion of Osobenus yakimae


Stonefly Species Osobenus yakimae (Yakima Springflies)

Species Range
Common Name
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