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Artistic view of a Male Pteronarcys californica (Pteronarcyidae) (Giant Salmonfly) Stonefly Adult from the Gallatin River in Montana
Pteronarcys californica

The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.

Dorsal view of a Glossosoma (Glossosomatidae) (Little Brown Short-horned Sedge) Caddisfly Larva from the Yakima River in Washington
I caught this tiny larva without a case, but it seems to key pretty clearly to to Glossosomatidae. From there, the lack of sclerites on the mesonotum points to either Glossosoma or Anagapetus. Although it's difficult to see in a 2D image from the microscope, it's pretty clear in the live 3D view that the pronotum is only excised about 1/3 of its length to accommodate the forecoxa, not 2/3, which points to Glossosoma at Couplet 5 of the Key to Genera of Glossosomatidae Larvae.
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 debilis (Mahogany Duns)

This widespread species can produce memorable hatches where it is locally abundant, especially in the West where it also tends to run larger in size. It loves the margins as is typical of most Leptophlebiidae species but has a greater tolerance for current. They are often found even in riffles. This is the most important species in the West.

Where & when

Time of year : July through October; peaks in September and October

Though they can begin to trickle off in the Summer, this species is most important in the Fall when its hatches concentrate. Added volume from other similar species of Paraleptophlebia can make these hatches of Mahogany Duns very important. When the hatch is at its greatest concentration, an added bonus is that there are often few competing insects on the water. It occurs across the continent and may be reinforced by Paraleptophlebia praepedita in the East or by one of several unusual tusk bearing species, Paraleptophlebia bicornuta, Paraleptophlebia packii and Paraleptophlebia helena in the West.

In 51 records from GBIF, adults of this species have mostly been collected during September (31%), August (27%), July (16%), October (14%), and June (8%).

In 35 records from GBIF, this species has been collected at elevations ranging from 194 to 9751 ft, with an average (median) of 479 ft.

Species Range

Hatching behavior

Time of day : Midday

Water temperature: 50-55°F

Spinner behavior

Time of day: Afternoon

Nymph biology

Current speed: Moderate

Leptophlebiidae species have a unique behavioral characteristic. They like to school and migrate to hatch sites like a little school of minnows. The angler fortunate enough to intercept them during this behavior can experience some fast and furious nymph fishing.

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: 8 mm
Wing length: 8-9 mm

This is a handsome, clear-winged, rich brownish, late-season species. Head above, thorax, and both ends of abdomen deep rich brown. Legs pale. Wings hyaline with pale veins. Costal cross veins obsolete except in the stigmatic area where they are numerous, simple, curved, and strongly aslant, and where the proximal end (next to subcosta) of each is obsolescent.

Abdomen white on segments 2 to 7, with brownish purple half-rings across the apices of the segments. A brown point on the spiracle, and a rounded brown spot before each spiracle above the lateral margin. Ganglia marked with yellow. Forceps with a large, ventral, basal lobe-like dilation. Penes separated by a U-shaped notch; each dilated at its outer end, narrowing the notch. On the outer side at the end there is a recurved lateral tooth. The reflexed spur is twice as long as the cleft is deep; it is arcuate, outcurving and acute at the apex (see fig. 134). Tails white.

This is a common species in the northeastern states.

Specimens of the Mayfly Species Paraleptophlebia debilis

1 Female Dun

Start a Discussion of Paraleptophlebia debilis


Mayfly Species Paraleptophlebia debilis (Mahogany Duns)

Species Range
Common Names
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