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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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Mayfly Species Cinygma integrum (Western Light Cahills)

Where & when

In 7 records from GBIF, adults of this species have been collected during June (29%), August (29%), April (29%), and July (14%).

In 1 record from GBIF, this species has been collected at elevation of 7000 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: 11 mm
Wing length: 12 mm

Head red-brown. Thoracic notum light red-brown; darker brown anteriorly and in postero-lateral areas. Pleura and sternum very similar in color, pleura with numerous blackish pencilings between wing roots and bases of legs. Fore leg yellowish to rather dark red-brown; two indistinct darker bands on femur, which is also narrowly darker at apex; apex of tibia blackish; basal tarsal joint somewhat more than 1/2 the length of the second. Middle and hind legs amber to light reddish brown; femora usually with two darker bands; in dark specimens, femora washed with purplish red. Wings hyaline; venation dark brown. A faint greyish tinge in stigmatic area and at base of fore wing. Cross veins in basal costal and subcostal spaces paler, rather indistinct; those in apical portion of costal space divided by a fine line near the costa into an upper series of small cells and lower series of larger ones, as in C. lyriformis (now a synonym of Cinygma lyriformi).

Abdominal segments 2-7 semi-hyaline. Tergite 2 largely purplish brown. Posterior margins of 3-7 dark purplish brown; geminate mid-dorsal line of same dark color, on each side of which is a whitish crescentic area. A wider dark purple-brown stripe between median line and pleural fold extends from posterior margin almost to anterior margin; between this dark stripe and pleural fold is another pale area. Sternites tinged with faint purplish brown. Segments 8-10 opaque; on tergites “the prevailing color becomes modified either with light burnt-umber or with opaque burnt-sienna or brown ochre, while the median stripe is posteriorly obliterated more or less in every segment, and in segments 8 and 9 the lateral stripes attain the base” (Eaton). Sternites light burnt-umber; no dark markings. Forceps and forceps base reddish brown. Tails light smoky greyish. Penes less distinctly lyre-shaped than in lyriformis, each division somewhat broader and notched at tip (see fig. 99).

The darker abdomen and differences in structure of penes serve to separate this species from lyriformis (now a synonym of Cinygma lyriformi) .

Start a Discussion of Cinygma integrum


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

Mayfly Species Cinygma integrum (Western Light Cahills)

Species Range
Common Name
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