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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.

Mayfly Genus Acentrella (Tiny Blue-Winged Olives)

The only Acentrella species commonly reported to be important to anglers is Acentrella turbida, though Acentrella insignificans is important in some western locales. See the species pages for distribution and timing details. This genus is one of two (including Heterocloeon) that can easily be distinguished from other Baetidae genera by the presence of a conical mesonotal projection. A. turbida lacks hindwings which is useful for distinguishing this species from all others in either genera. A. turbida was previously known by the names of its synonyms Pseudocloeon turbidum in the West and Pseudocloeon carolina in the East.

Hatching behavior

Time of day : Early evening; sometimes all day

The nymphs are normally excellent swimmers, but they become much less mobile as they're emerging and dead-drift helplessly to the suface. Considering that they then emerge and fly away quickly, this makes the nymphs the prime stage to match during this emergence.

Spinner behavior

Time of day: Dusk

These species molt into spinners and mate the same day they emerge. The spinner activity usually comes at dusk, or even after dark.

Nymph biology

Current speed: Slow to Medium

Substrate: Rocks, logs, gravel, vegetation

Environmental tolerance: Widely tolerant, but best in cold rivers

Specimens of the Mayfly Genus Acentrella

3 Female Spinners
1 Male Spinner
Male Acentrella turbida (Tiny Blue-Winged Olive) Mayfly Spinner
I would not like to have to match this hatch. These are the smallest mayflies I have ever seen. I used to think Caenis was the smallest adult mayfly in the west but these guys are about 4mm long. The male eyes are two toned, brown above and olive below. The abdomen is dark brown interspersed with light brown. The abdomen is clear for the anterior 2/3rd and the remainder is white. The tails are twice as long as the insect. There is only one pair of wings.
1 Male Dun
Male Acentrella insignificans (Tiny Blue-Winged Olive) Mayfly Dun
This specimen emerged indoors from nymphs I had collected, then partly molted into a spinner but got stuck along the way. I've included a couple pictures showing some of the spinner colors. It got a bit waterlogged after emerging, so the wings aren't in perfect shape, but it still represents one of two Baetids that were emerging and drawing trout to rise on the Yakima. Based on body size and shape, it is most likely the same species as this nymph.
1 Female Dun
Female Acentrella (Tiny Blue-Winged Olives) Mayfly Dun
I've lost the date information for this specimen and taken a guess.
1 Nymph
Male Acentrella insignificans (Tiny Blue-Winged Olive) Mayfly Nymph
Another nymph probably of the same species as this one emerged and was photographed as a dun and partly-molted spinner.

2 Streamside Pictures of Acentrella Mayflies:

Recent Discussions of Acentrella

acentrella nymph
20 replies
Posted by Goose on Nov 3, 2006
Last reply on Sep 3, 2011 by Oldredbarn
Hi Jason! Do you have a picture of the (acentrella-miniature BWO nymph) on the site? I've been fishing them and wanted a better idea of how they look.

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  • Fauceglia, Ted. 2005. Mayflies . Stackpole Books.
» Genus Acentrella (Tiny Blue-Winged Olives)
Species in Acentrella
Acentrella insignificansTiny Blue-Winged Olive221
Acentrella parvulaMiniature Blue-Winged Olive00
Acentrella turbidaTiny Blue-Winged Olive421
5 species (Acentrella alachua, Acentrella barbarae, Acentrella feropagus, Acentrella lapponica, and Acentrella nadineae) aren't included.
Genus Range
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