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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.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Mayfly Species Paraleptophlebia bicornuta (Mahogany Duns)

This important Western species is one of the few mayflies outside the Ephemeridae family to possess large tusks on the front of its head. It is also one of the largest species of Paraleptophlebia.

P. bicornuta is often reinforced by simultaneous hatches of the more common Paraleptophlebia debilis. The two duns appear virtually identical to the naked eye, though bicornuta usually has an edge in size.

Paraleptophlebia bicornuta is by far the widest distributed tusked species, though there are others. Telling the tusked species apart is very difficult and even entomological texts are largely ambiguous on the characters that differentiate them. Distribution records are probably the most reliable way for anglers to know with any probability what they are looking at. Check out the Paraleptophlebia packii and Paraleptophlebia helena hatch pages for more distribution information.

Where & when

Time of year : September through early November

In 5 records from GBIF, adults of this species have been collected during October (40%), August (20%), June (20%), and September (20%).

Species Range

Hatching behavior

Time of day : Morning and afternoon

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: 9 mm
Wing length: 10 mm

This is a species with almost as much brown as white on the middle abdominal segments. Head and thorax blackish brown above, a little paler on the sides and beneath. Fore legs brown with paler tarsi; middle and hind legs paler beyond the brown femora. Wings hyaline with brown longitudinal veins; costal cross veins obsolete except in the stigmatic area where they are numerous, long, strongly aslant and sometimes forked.

Abdomen dark brown on the first segment above, lighter on the second, and reddish brown on segments 8 to 10; 3 to 7 whitish with brownish cloud on the posterior half of the dorsum of each. A black dot on the stigma and a diffuse roundish, brown spot above it. Mid-ventral areas also faintly tinged with brown, especially segment 7. Sternite 1 wholly brown; 8 and posterior half of 9 a bright reddish brown. The basal joint of the forceps is brown; the distal joints are white; at the base of the former is a conspicuous lobe above, similar to that in Paraleptophlebia debilis. Penes broadly separated by a very wide U-shaped notch; dilated and truncate at tips and bearing just before the tips on the dorsal side a pair of long flat lobes that converge by their rounded ends within the U-shaped cleft. Reflexed spur bifid, almost crescentic in form, attached by the back of this crescent; the outer horn longer (see fig. 135). Tails pale brown.

Specimens of the Mayfly Species Paraleptophlebia bicornuta

1 Male Dun
1 Male Spinner
1 Female Spinner
2 Nymphs

Start a Discussion of Paraleptophlebia bicornuta

References

Mayfly Species Paraleptophlebia bicornuta (Mahogany Duns)

Species Range
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