This genus is not well-known to fly fishers because most of its species were, until very recently, classified as either Centroptilum or Cloeon.
» Genus Procloeon (Tiny Sulphur Duns)
(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, Procloeon viridoculare)
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 & WhenTime Of Year (?): Mostly summer
Preferred Waters: Best in alkaline (Alkaline: Having a pH higher than 7 (opposite of acidic). Moderately alkaline water is ideal for trout because it's better for the growth of phytoplankton, the usual base of the aquatic food chain, and that's good for the growth of everything higher up the chain, including trout.) streams
Time Of Day (?):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 (Dead-drift: The manner in which a fly drifts on the water when not moving by itself or by the influence of a line. Trout often prefer dead-drifting prey and imitating the dead-drift in tricky currents is a major challenge of fly fishing.) float to the surface, buoyed by gases they release.
Different sources say mid-evening or early morning
According to one source, the duns crawl out onto shore to emerge.Spinner BehaviorProcloeon duns usually molt into spinners, mate, and die the very day they hatched. Dun and spinner activity may overlap.Nymph Biology
Current Speed: SlowThey either prefer fertile, weedy spring creeks, or slow, silty stretches of relatively warm trout rivers, depending on which books should be believed.
Substrate: Many, but weeds are best
Pictures of 2 Mayfly Specimens in the Genus Procloeon:
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