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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.

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.
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Mayfly Genus Procloeon (Tiny Sulphur Duns)

This genus is not well-known to fly fishers because most of its species were, until very recently, classified as either Centroptilum or Cloeon.

These mayflies may be abundant enough to cause fishable hatches in spite of their tiny size.

It's difficult to discern from previous angling literature exactly which statements now apply to Procloeon, because its species come from other little-known genera and the accounts for them conflict. They were mentioned in combination with other genera, adding to the confusion. So the information below is highly tentative and, where accounts seem to conflict, both have been given.

Where & when

Time of year : Mostly summer

Preferred waters: Best in alkaline streams

In 71 records from GBIF, adults of this genus have mostly been collected during July (30%), August (27%), June (27%), September (7%), and October (6%).

In 100 records from GBIF, this genus has been collected at elevations ranging from 3 to 29016 ft, with an average (median) of 1411 ft.

Genus Range

Hatching behavior

Time of day : Different sources say mid-evening or early morning

Trout may feed well on the tiny nymphs during a hatch. Caucci and Nastasi discovered and noted in Hatches II that these nymphs, despite their excellent swimming ability most of the time, become nearly immobile shortly before hatching. They slowly crawl out of the water or dead-drift float to the surface, buoyed by gases they release.

According to one source, the duns crawl out onto shore to emerge.

Spinner behavior

Procloeon duns usually molt into spinners, mate, and die the very day they hatched. Dun and spinner activity may overlap.

Nymph biology

Current speed: Slow

Substrate: Many, but weeds are best

They either prefer fertile, weedy spring creeks, or slow, silty stretches of relatively warm trout rivers, depending on which books should be believed.

Specimens of the Mayfly Genus Procloeon

1 Female Dun
1 Nymph

Start a Discussion of Procloeon


Mayfly Genus Procloeon (Tiny Sulphur Duns)

Genus Range
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