Header image
Enter a name
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.

Ventral view of a Hydropsyche (Hydropsychidae) (Spotted Sedge) Caddisfly Larva from the Yakima River in Washington
With a bit of help from the microscope, this specimen keys clearly and unsurprisingly to Hydropsyche.
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 Iswaeon anoka (Tiny Blue-Winged Olives)

This tiny hind-wingless Midwestern and Western species can produce excellent hatches because it is so extremely abundant. Its bright green duns are unmistakable. In the West they can also be an equally unmistakable bright almost fluorescent chartreuse, especially as nymphs. They are very common in the Northwest and Rocky Mountain states, with their population densities giving way to the similarly tiny and hind-wingless (though more somber colored) Acentrella species in Southern Oregon, California and the Southwest.

Iswaeon anoka was first brought to the attention of the angling community (as Pseudocloeon anoka) by famous angling author and columnist Joe Brooks. Back in the late 60's he wrote an article for Outdoor Life magazine extolling the work of Doug Swisher and Carl Richards in their forthcoming and groundbreaking book, Selective Trout. This species was featured as the model for their now famous version of the "No-Hackle" dry fly and imitative parachute patterns, sparking a revolution in fly design for hyper-selective trout. The rest as they say, is history...

Taxonomic History

This species appears in some angling literature under the former names Pseudocloeon anoka in the Midwest and Pseudocloeon edmundsi in the West.

Where & when

Time of year : Late June through late July; again from August through October

In 10 records from GBIF, adults of this species have been collected during July (40%), May (30%), June (20%), and September (10%).

In 4 records from GBIF, this species has been collected at elevations of 3, 26, 886, and 1089 ft.

Species Range

Hatching behavior

Fred Arbona says of Iswaeon anoka (as Pseudocloeon anoka) hatching behavior in Mayflies, the Angler, and the Trout that:

The little nymph can easily crawl out of the water during emergence, and therefore the trout are able to consume them en masse very close to the bank.

This is somewhat open to interpretation and it is suspected they emerge on the surface as well.

Nymph biology

Substrate: Gravel, vegetation

The nymphs are reported to prefer shallow water near the banks.



There's a great blog post on Aquatic Insects of Central Virginia about identifying Iswaeon anoka.

Start a Discussion of Iswaeon anoka


Mayfly Species Iswaeon anoka (Tiny Blue-Winged Olives)

Species Range
Troutnut.com is copyright © 2004-2024 (email Jason). privacy policy