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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.

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

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
Female Procloeon (Tiny Sulphur Duns) Mayfly Dun
This dun of a fairly large Baetidae species was one of only a couple I saw all evening.
1 Nymph
Procloeon pennulatum (Tiny Sulphur Dun) Mayfly Nymph
This fragile nymph is easily damaged during sampling making identification more difficult.

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» Genus Procloeon (Tiny Sulphur Duns)
Species in Procloeon
Procloeon ingensTiny Sulphur Dun00
Procloeon insignificansTiny Sulphur Dun00
Procloeon mendaxTiny Sulphur Dun00
Procloeon pennulatumTiny Sulphur Dun11
Procloeon rubropictumTiny Sulphur Dun00
Procloeon rufostrigatumTiny Sulphur Dun00
Procloeon simplexTiny Sulphur Dun00
Procloeon venosumTiny Sulphur Dun00
14 species (Procloeon bellum, Procloeon caliginosum, Procloeon distinctum, Procloeon fragile, Procloeon inanum, Procloeon intermediale, Procloeon nelsoni, Procloeon ozburni, Procloeon quaesitum, Procloeon rivulare, Procloeon simile, Procloeon texanum, Procloeon vicinum, and Procloeon viridoculare) aren't included.
Genus Range
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