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Salmonflies
Pteronarcys californica

The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.

Mayfly Species Caudatella heterocaudata

This species is quite rare, but Fred Arbona in Mayflies, the Angler, and the Trout says creates "fair" hatches in places.

Where & when

Time of year : July and August

Hatching behavior

Time of day : Midday

Nymph biology

Current speed: Fast

Physical description

Most of these descriptions are direct 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.

Body length: 6–7 mm
Wing length: 6.5–7.5 mm

Eyes reddish-brown. Thorax olivebrown, yellowish patch anterior to the base of the wing, containing a black line which descends to the coxa of the foreleg; lateral sutures marked with black; legs pale olive-brown; fore femora and tibia with black markings; wings hyaline with pale veins and cross veins. Abdominal terga olive-brown, anterior half of each of the first four segments with broad black bands, bands on posterior segments reduced to large semicircular dorsal patches; sterna pale olive-brown with ~midventral and sublateral longitudinal dark brown stripes as in fig. 7. Caudal filaments brown, lateral cerci 20%-30% as long as terminal filament. Penes with a shallow median apical depression as in fig. 3.

Body length: 6–7 mm
Wing length: 6.5–7.5 mm

Similar to male except for usual sexual differences.

Body length: 7–8 mm

Cerci 2-3 mm long; terminal filament 10-12 mm long. Head brown with pale markings, roughened but without occipital tubercles; antennae brown ; maxillary palpi three-segmented as in fig. 12. Thorax brown; legs brown, femora with a few marginal spines and a distinct row of marginal hairs, tibiae and tarsi with a distinct row of marginal hairs (fig. 15), tarsal claws with three to seven denticles. Abdominal terga olive-brown; anterior half of each of the first four segments with broad black bands, bands on posterior segments reduced to large semicircular dorsal patches; each tergum with a series of lateral black patches; paired dorsal abdominal tubercles on segments 1-9 or 2-9 as in figs. 1 and 23; sterna pale olive-brown with median and paired sublateral longitudinal dark brown stripes as in fig. 7. Caudal filaments light brown, darker at the joinings; lateral cerci 20% to 30% as long as terminal filament.

Specimens of the Mayfly Species Caudatella heterocaudata

1 Male Dun
Male Caudatella heterocaudata  Mayfly Dun
A few days after unexpectedly collecting a female dun of this species, but in a sad, bedraggled shape, I went back to the same pool to see if I could find more. I was able to catch this one male dun during a dusk emergence dominated by other species, and he made it home in prime shape for photos.
1 Female Dun
Female Caudatella heterocaudata  Mayfly Dun
These duns were emerging sporadically throughout a cloudy evening at the end of June. Had I looked more closely when I caught this one and realized it represented my first collection of this genus, or just noticed the really striking coloration, I would have set my fly rod on shore and spent more time lurking mid-river with my net trying to catch more of them emerging (and at least one in better shape).

It's always a bit difficult to identify a female dun, but in this case the three longitudinal stripes on the sternites are very distinctive and narrow the choices to Caudatella heterocaudata and Caudatella columbiella. However, the length of the fore wing measured with a caliper is 7.25 mm, whereas columbiella should be no more than 6 mm, so heterocaudata appears to be the correct ID.

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References

  • Allen, R.K., and Edmunds, George F. Jr. 1961. A Revision of the Genus Ephemerella (Ephemeroptera: Ephemerellidae) II. The Subgenus Caudatella. Annals of the Entomological Society of America 54: 603-612.
  • Arbona, Fred Jr. 1989. Mayflies, the Angler, and the Trout. Nick Lyons Books.
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