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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 Kogotus (Perlodidae) Stonefly Nymph from Mystery Creek #199 in Washington
This one pretty clearly keys to Kogotus, but it also looks fairly different from specimens I caught in the same creek about a month later in the year. With only one species of the genus known in Washington, I'm not sure about the answer to this ID.
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 Caudatella columbiella

Taxonomic History

This species was previously considered synonymous with the more common Caudatella heterocaudata, but it was given the status of a separate species by Taxonomic Review of the Caudatella heterocaudata (McDunnough) and C. hystrix (Traver) Complexes (Insecta: Ephemeroptera: Ephemerellidae).
Species Range


To determine whether a specimen of Caudatella belongs to Caudatella columbiella, use the Key to Species of Caudatella Nymphs.

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.


Described in Jacobus 2010 (2010)

Similar to Caudatella heterocaudata, but different in that Caudatella columbiella has paired medial spines on abdominal tergum 1, the other paired medial spines sharp at the tips, and cerci that are approximately one-sixth the length of the median filament, or about one-half the length of the abdomen.

Male Spinner

Described in Jacobus 2010 (2010)
Wing length: 6 mm

Similar to Caudatella heterocaudata, but different in that male adults of Caudatella columbiella (forewing length ca. 6 mm) are smaller than those of Caudatella heterocaudata (forewing length at least 7mm), and Caudatella columbiella male adults usually have abdominal maculation that is not as highly contrasted from the base coloration.

Male Spinner

Described in Needham et al (1935) as Ephemerella heterocaudata
Body length: 6.5 mm
Wing length: 7 mm

Eyes dark reddish brown. Thorax dark olive brown, the pronotum with considerable black shading. Median and lateral sutures of the mesonotum black-marked. A yellowish patch within which is a black line lies anterior to the wing base; the black line continues to the fore coxa. Mesosternum blackish brown with olive brown shading. Legs deep olive; fore femur and tibia tinged with black; fore tarsus about equal in length to the tibia, and both of these joints longer than the femur. Wings hyaline; longitudinal veins somewhat smoky, cross veins pale. Abdominal tergites olive brown; the first four tergites with broad black bands anteriorly, which bands are reduced to semicircular dorsal patches on the posterior tergites. A series of lateral black patches is also present, which tend to fuse with the dorsal bands on the anterior segments. Sternites pale olive; an irregular mid-ventral black band and similar black lateral bands. Forceps smoky, the third joint short. Penes united, forming an upcurved rod. (See fig. 156) Tails smoky, the middle one twice as long as the outer ones.


Described in Needham et al (1935) as Ephemerella heterocaudata

Nymph with well-developed dorsal abdominal spines; head and thorax smooth; black abdominal markings as in the imago; middle tail much longer than the outer ones.

Head and thorax of nymph smooth. Legs rather short; femora somewhat flattened. Lateral extensions of the abdominal segments practically wanting, the postero-lateral spines not produced. Gills present on tergites 3-7. Dorsal spines prominent, strong; incurved, becoming progressively longer and further apart from tergite 2 to 7, but shorter and closer together on tergites 8-9. General color dark brown, the head blackish; legs without pale bands. Abdominal sternites with a mid-ventral reddish brown streak and on each side a lateral row of brownish dashes. Tails brownish, the joinings darker; middle tail almost three times the length of the outer ones.

Start a Discussion of Caudatella columbiella


Mayfly Species Caudatella columbiella

Species Range
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