Header image
Enter a name
Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

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.


Like most common names,"Springfly" can refer to more than one taxon. They're previewed below, along with 5 specimens. For more detail click through to the scientific names.

Stonefly Genus Helopicus

These are pretty much always called Springflies.
Lateral view of a Female Helopicus subvarians (Perlodidae) (Springfly) Stonefly Adult from the West Branch of the Delaware River in New York
I caught this female during her egg-laying flight.

Stonefly Genus Megarcys

These are pretty much always called Springflies.
Megarcys subtruncata (Perlodidae) (Springfly) Stonefly Adult from the Touchet River in Washington

Stonefly Genus Perlinodes

These are pretty much always called Springflies.
Female Perlinodes aurea (Perlodidae) (Springfly) Stonefly Adult from the Touchet River in Washington

Stonefly Species Perlinodes aurea

These are pretty much always called Springflies.
Female Perlinodes aurea (Perlodidae) (Springfly) Stonefly Adult from the Touchet River in Washington

Stonefly Genus Cultus

These are often called Springflies.
Dorsal view of a Cultus tostonus (Perlodidae) (Springfly) Stonefly Nymph from the Cedar River in Washington
This specimen keys pretty well to Cultus. Key characteristics observed under the microscope but not necessarily apparent on my photo are the lack of submental gills (or any gills at all), the lack of short, stout setae on the occiput or anterolateral prothoracic margins, and the lack of a low knob below the subapical tooth on the lacinia. Species known to be found in Washington are Cultus pilatus and Cultus tostonus. It clearly does not fit the description by Frison (1942) of Diploperla pilata, as Cultus pilatus was first named. I cannot find a detailed description of the nymph of tostonus, but Ricker 1952 describes a defining character of the adults, "Head mostly yellow, the only important dark marking being the bands which join the anterior to the lateral ocelli ; median pronotal stripe, at its middle, about one-fifth of the width of the pronotum." The nymph shows a very dark pattern fitting that description on the head (likely retained into adulthood) and the pronotal stripe is about the right width, too. Given that visual description, the range, and the poor fit to pilatus, I'm calling this Cultus tostonus.

Stonefly Genus Isogenoides

These are often called Springflies.
Isogenoides olivaceus is a common species.
Dorsal view of a Isogenoides hansoni (Perlodidae) (Appalachian Springfly) Stonefly Nymph from Mongaup Creek in New York
This large Perlodidae stonefly was a strikingly bright yellow color, more so than any other insect I've seen. I didn't enhance it much. See the discussion threads to follow how we identified this specimen, which was listed incorrectly for several years.

Stonefly Species Megarcys subtruncata

These are often called Springflies.
Megarcys subtruncata (Perlodidae) (Springfly) Stonefly Adult from the Touchet River in Washington
Troutnut.com is copyright © 2004-2024 (email Jason). privacy policy