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Artistic view of a Male Pteronarcys californica (Pteronarcyidae) (Giant Salmonfly) Stonefly Adult from the Gallatin River in Montana
Pteronarcys californica

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

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 Rhithrogena jejuna (Dark Red Quills)

Where & when

Time of year : May to early June

The Leonards note in Mayflies of Michigan Trout Streams that both the nymphs and the adults are often found together with Rhithrogena impersonata.

In 17 records from GBIF, adults of this species have been collected during May (53%), June (29%), July (12%), and August (6%).

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: 8-9 mm
Wing length: 9-10 mm

A species of the jejuna-undulata group, having no lateral spines near base of penes; tips of penes narrowed, distinctly outcurved.

Thoracic notum dull reddish black; pleura and sternum very similar. Legs sooty brown; fore tibia blackish at apex; all femora with a black streak longitudinally, which commences near base and is tapered at each end. Wings hyaline; membrane very faintly tinted with greyish, not noticeably darker in stigmatic area. Venation pitch-brown. About 3 basal costal cross veins and 19 beyond the bulla, many of which are anastomosed. Abdominal segments 2-5 “translucent burnt-umber brown” (Eaton); posterior margins of tergites darker; sternites slightly paler than tergites. Apical segments very similar in color, somewhat opaque. Forceps brown; tails reddish brown. Genitalia as in fig. 102.

This species is allied to Rhithrogena undulata and Rhithrogena impersonata in genitalic type. The lack of small apical spines and the outcurved tips of the penes separate this species from Rhithrogena impersonata; the penes are likewise distinctly narrowed at the tips, by which character it may be distinguished from R. undulata.

Start a Discussion of Rhithrogena jejuna


Mayfly Species Rhithrogena jejuna (Dark Red Quills)

Species Range
Common Names
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