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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
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.

Dorsal view of a Sweltsa (Chloroperlidae) (Sallfly) Stonefly Nymph from the Yakima River in Washington
This species was fairly abundant in a February sample of the upper Yakima.
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 Species Apobaetis futilis (Tiny Blue-Winged Olives)

This hind wingless little mayfly was formerly known as Pseudocloeon futile and can hatch in excellent numbers in certain western locales.

Where & when

Time of year : Late summer

Caucci and Nastasi report in Hatches II that large Rocky Mountain spring creeks have excellent hatches of this species.
Species Range

Physical description

Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.

Male Spinner

Described in Needham et al (1935) as Pseudocloeon futile
Body length: 3 mm
Wing length: 3.5 mm

Abdominal tergites of male imago clay-brown.

Turbinate eyes rather lengthily oval, well separated; light olive or greenish brown in dried specimen. Head brownish between the eyes; antennae pale smoky. Thorax deep clay-brown; traces of ruddy shading on the pleural sutures; scutellum of the mesonotum, and anterior portion of metanotum paler. Legs dull dirty whitish. Wings hyaline, venation pale. 4 or 5 oblique cross veins in the stigmatic area, with no granulations between them; paired intercalaries rather long and well developed except in the first and second interspaces. Abdominal tergites 2-6 clay-brown, very similar in color to the thorax; the triangular portion of tergite 1 paler, more ochreous. Tergites 7-10 paler, rather ochreous; traces of ruddy lateral shading, on some specimens; Sternites considerably paler, the apical ones shading into cream-color, with traces of ruddy streaks on the lateral margin. Tails pale; forceps pale creamy, widely separated at the base.

The shape and color of the eyes and the clay-brown of thorax and abdomen separate this species from P. turbidum (now a synonym of Acentrella turbida) and P. carolina (now a synonym of Acentrella turbida).

Discussions of Apobaetis futilis

Possible ID
1 replies
Posted by Sreyadig on Apr 11, 2021
Last reply on Apr 11, 2021 by Taxon
In searching for nymphs in my small stream in northern Maryland, 500 yards from the PA line, I came across a 2 tailed mayfly that was not a of the Epeorus genus.

It was in a fast riffle section along with Epeorus nymphs. This was about 3/8” in overall length including tails. Darker straw coloration with dark brownish black wing cases that were pronounced in color and shape. Biggest factor was the tails. Median caudal filament was truncated, very small compared to the outer pair. Not even sure if tail/ caudal filament should be used to describe. In my books the closest thing is the Pseudocloeon futile. Which is an old taxonomic name I’m finding out.

This find seems rare in my area and experience. Hopefully I can get a photo...

Start a Discussion of Apobaetis futilis


  • Caucci, Al and Nastasi, Bob. 2004. Hatches II. The Lyons Press.
  • Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.

Mayfly Species Apobaetis futilis (Tiny Blue-Winged Olives)

Species Range
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