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Mayfly Species Iswaeon anoka (Tiny Blue-Winged Olive)

This tiny hind-wingless Midwestern and Western species can produce excellent hatches because it is so extremely abundant. It appears in previous angling literature under the former names Pseudocloeon anoka in the Midwest and Pseudocloeon edmundsi for its western synonym (Synonym: A former name of a taxon, usually a species. Entomologists frequently discover that two insects originally described as different species are one in the same, and they drop one of the names. The dropped name is said to be a synonym of the remaining name. These changes take a while to trickle into the common knowledge of anglers; for example, Baetis vagans is now a synonym of Baetis tricaudatus.). 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...

Where & When

Regions: Midwest, West

Time Of Year (?): Late June through late July; again from August through October

Hatching Behavior

Fred Arbona says of Iswaeon anoka (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.

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