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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.

Ventral view of a Hydropsyche (Hydropsychidae) (Spotted Sedge) Caddisfly Larva from the Yakima River in Washington
With a bit of help from the microscope, this specimen keys clearly and unsurprisingly to Hydropsyche.
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 Baetis pluto (BWOs)

Where & when

In 6 records from GBIF, adults of this species have been collected during June (50%), July (33%), and August (17%).

In 3 records from GBIF, this species has been collected at elevations of 1220, 1339, and 1775 ft.

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

Body length: 4.5 mm
Wing length: 4.5 mm

Abdominal tergites 2-8 of male imago largely maroon brown, with pale hyaline areas on the lateral and anterior margins; genitalia of the Baetis intercalaris type, having no tubercle on the inner apical margin of the first forceps joint.

Turbinate eyes moderate; deep black-brown. Head and thorax shiny blackish. Lateral margin of mesonotum, anterior to the wing roots, brown; a light brown spot on the antero-lateral corner of mesonotum; pleural sutures shaded with brown. Legs dull ochreous, tibiae and tarsi paler than the femora. Wings hyaline, venation pale. Heavy granulations present between the cross veins of the stigmatic area of the fore wing; cross veins anastomosed. First pair of intercalaries obsolescent, second pair rather short, third pair well developed, long. Hind wing almost three times as long as its width; third vein well developed, running beyond the middle of the hind margin. Between veins 2 and 3 is one long intercalary, and a shorter somewhat obsolescent one. Traces of two short intercalaries between veins 1 and 2.

Abdominal tergites 2-6 semi-translucent, deeply tinged with maroon brown on most of each tergite; along the lateral and anterior margins, however, are pale hyaline areas. Tergites 7-10 opaque maroon brown. Sternites 2-6 pale hyaline; 7-10 opaque, whitish with brown tinges. Tracheae of the spiracular area prominently marked with black. Tails white. Forceps brown-tinged. There is no tubercle on the inner apical margin of the first forceps joint.

The maroon-brown of the abdomen and the blacker thorax, as well as the absence of the forceps tubercle, distinguishes this species from Baetis rusticans. The abdominal markings are darker than in B. levitans (now a synonym of Baetis flavistriga).


Start a Discussion of Baetis pluto

References

  • Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.

Mayfly Species Baetis pluto (BWOs)

Taxonomy
Species Range
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