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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 Paraleptophlebia sculleni

Where & when

Time of year : Summer

To my knowledge, this species has only been described in the scientific literature from the Oregon Cascades. However, on July 25th, I found several swarms of a dozen or so male spinners dancing above a gravel road/trail on the rim of a bouldery canyon at 2800 feet elevation on the eastern slope of the Washington Cascades.

Although this canyon would easily constitute class 4+ whitewater when flows are higher, at typically low summer flows there are lots of quiet backwaters in the pools between the fast drops and boulders. This might be the habitat for the Paraleptophlebia nymphs.

I found them again a couple weeks later on the Middle Fork Snoqualmie River on the west slope of the Washington Cascades.

In 7 records from GBIF, adults of this species have been collected during June (43%), July (29%), and August (29%).

Species Range

Spinner behavior

The male spinners I encountered were flying right at dusk.

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: 6.5 mm
Wing length: 6.5 mm

This is another brown and white, clear-winged species with black-ringed abdomen. Thorax brown above with paler sutural lines on the sides. Legs pale. Wings hyaline. Costal cross veins obsolete except in the creamy stigmatic area which covers costal and subcostal interspaces. Stigmatic cross veins few, simple, slightly curved.

Abdomen brown on segments 1 and 8 to 10; light brown on 2 and 7; white on 3 to 6, and on the base of 7, with blackish apical half-rings and lateral stripes that are darker at the postero-lateral angles of the segment. Ganglia and venter of segments 7 to 9 yellowish. The basal segment of the forceps tapers suddenly at the base, then very slightly to its tip. The penes are separated by an oval U-shaped notch, longest at the inner angle which projects rearward in a rounded lobe. Lateral to this lobe the apex is obliquely truncate, ending laterally in a minute recurved hook; the reflexed spurs are elongate, sickle-shaped and incurving at the tip (see fig. 133).

Specimens of the Mayfly Species Paraleptophlebia sculleni

2 Male Spinners

Start a Discussion of Paraleptophlebia sculleni


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

Mayfly Species Paraleptophlebia sculleni

Species Range
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