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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.

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 Genus Siphlonurus (Gray Drakes)

The important Eastern species are Siphlonurus quebecensis, Siphlonurus alternatus, and to a lesser extent Siphlonurus rapidus. All may produce fishable spinner falls, often with more than one species in the same swarm, but these are generally localized and minor events compared to the classic superhatches.

The main Western species, Siphlonurus occidentalis, is much more valuable. Its importance in the West is often compared to that of Isonychia in the East.

Where & when

Preferred waters: Slow, alkaline streams and lakes

Siphlonurus hatches are generally slow-paced events, and it takes two to three months for the entire generation to hatch out of a given stretch of water. See the species pages for emergence details about each one.

In 215 records from GBIF, adults of this genus have mostly been collected during June (46%), July (27%), May (12%), and August (12%).

In 361 records from GBIF, this genus has been collected at elevations ranging from -30 to 11444 ft, with an average (median) of 804 ft.

Genus Range

Hatching behavior

Time of day : Morning through midday

Habitat: Slow, shallow water

Water temperature: Varies, but 60-63°F is ideal

There is some disagreement about exactly how Siphlonurus duns hatch. It is certain that they crawl out onto shore sometimes and hatch on the surface at other times, but which of these behaviors is more prominent is anybody's guess.

The time of emergence is also up in the air; most say it is in the morning, but there are reports of emergence in the afternoon and in the middle of the night, as well. One account suggests it is most common in the evening.

Authors generally agree that, regardless of hatching mode or time, the duns are the least important stage of this species. There are reports of trout feeding well on them, and this is sometimes attributed to the wind blowing the duns into the water.

In Mayflies Ted Fauceglia relays a detailed account by Dick Stewart of the hatching of Siphlonurus duns, quoted here in part:

They then emerge by swimming toward the surface and immediately taking flight. They pop through the surface film like miniature helicopters rising toward the open sky. We believe that molting takes place either very quickly or when the duns are high in the trees, for try as we might, we almost never can find a dun (day or night) despite the fact that we can locate hundreds of spinners.

Another point on which most agree is that Siphlonurus duns emerge from very shallow margins and backwaters, sometimes far from the trout in the main channel.

Spinner behavior

Time of day: Usually dusk in the East and Midwest, morning in the West, sometimes afternoon in cold weather

Gray drakes return as spinners two to four days after hatching as duns, and they gather in swarms over the riffles. Accounts of their ovipositing behavior vary: some say the females repeatedly dive and dip their abdomens briefly into the water, while others say they drop their eggs from the air. Both genders eventually fall spent, but the spinner falls may be tricky to locate because the females sometimes fly far upstream after mating but before ovipositing. Trout may feed on Siphlonurus spinners very selectively.

Nymph biology

Current speed: Slow

Substrate: Silt, vegetation

Siphlonurus nymphs are not completely intolerant of medium to fast current, but their best populations are found in slow streams or still waters, often with plenty of weed growth. They are more frequently important to fly fishers than the duns.

They are extremely adept swimmers.

Specimens of the Mayfly Genus Siphlonurus

2 Female Duns
5 Male Spinners
7 Female Spinners
10 Nymphs

3 Underwater Pictures of Siphlonurus Mayflies:

Start a Discussion of Siphlonurus


Mayfly Genus Siphlonurus (Gray Drakes)

Genus Range
Common Names
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