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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.

Lateral view of a Male Baetidae (Blue-Winged Olive) Mayfly Dun from Mystery Creek #308 in Washington
This dun emerged from a mature nymph on my desk. Unfortunately its wings didn't perfectly dry out.
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 undulata (Small Western Red Quills)

This is one of the two most common species of Rhithrogena.

Where & when

Time of year : Mid-June through August

In 5 records from GBIF, adults of this species have been collected during June (20%), September (20%), April (20%), May (20%), and July (20%).

In 1 record from GBIF, this species has been collected at elevation of 5066 ft.

Species Range

Hatching behavior

Rhithrogena undulata duns escape their nymphal shucks underwater, but instead of emerging on the stream bed like most Rhithrogena species, they wait until they are within inches of the surface.

Swisher and Richards in Selective Trout say the duns are unimportant.

Spinner behavior

Time of day: Dusk

Knopp and Cormier call the spinner falls of Rhithrogena undulata "spectacular," and others mention that they are fishable.

Nymph biology

Current speed: Slow to medium

These nymphs prefer slower water than the others in their genus.

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: 7.5 mm
Wing length: 9 mm

A species of the jejuna-undulata group, having no basal lateral spines on penes; tips of penes broad, distinctly outcurved.

Head and thorax dark brown; several yellow spots on pleura. Fore legs brownish; apex of tibia darker. Middle and hind legs pale; dark streaks on femora. Wings hyaline; venation brown. Stigmatic area tinged with smoky; cross veins in this region mostly simple. Abdominal tergites dark brown; lateral margins very narrowly pale. Sternites very pale. Forceps dark brown, tails paler brown. Apices of penes broad, distinctly outcurved; no basal lateral spine, nor small spines near apex (see fig. 102).

Allied to Rhithrogena jejuna and Rhithrogena impersonata. Tips of penes outcurved as in R. jejuna, but not narrowed as in that species; no small apical spines such as occur in R. impersonata.

Specimens of the Mayfly Species Rhithrogena undulata

1 Male Spinner
1 Female Spinner

Start a Discussion of Rhithrogena undulata


Mayfly Species Rhithrogena undulata (Small Western Red Quills)

Species Range
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