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Mayfly Genus Rhithrogena

Taxonomic Navigation -?-
» Genus Rhithrogena
Species in RhithrogenaNumber of SpecimensNumber of Pictures
Rhithrogena futilisWestern Gordon Quill00
Rhithrogena hageniWestern Black Quill00
Rhithrogena impersonataDark Red Quill319
Rhithrogena jejunaDark Red Quill00
Rhithrogena manifesta00
Rhithrogena morrisoniWestern March Brown25
Rhithrogena robusta25
Rhithrogena undulataSmall Western Red Quill00
Rhithrogena virilis23

14 species aren't included.
Pictures Below ↓
This genus is widespread across the country, but it is only of major importance to anglers in the West.

The best hatches come from Rhithrogena morrisoni, Rhithrogena hageni, and Rhithrogena undulata. Even the less common species , Rhithrogena futilis, and Rhithrogena robusta are probably more important than any of their Eastern counterparts.

The East/Midwest species are Rhithrogena jejuna, Rhithrogena manifesta, and Rhithrogena impersonata, which is arguably the most important of a minor group. All of them are widespread and none of them are abundant except in rare locations, mostly in Michigan and Wisconsin.

Hatching Behavior


Most evidence points to Rhithrogena species emerging underwater. They usually do so on the stream bottom and float all the way to the surface as duns, but those emerging from slow water will rise most of the way as nymphs before struggling free of their shucks (
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Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.
Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.
Shuck: The shed exoskeleton left over when an insect molts into its next stage or instar. Most often it describes the last nymphal or pupal skin exited during emergence into a winged adult.). How slow is slow? Depth and temperature are also suspected of playing a role, so whether to fish a nymph, a sunken emerger or dun imitating wet fly usually remains open to experimentation in any given hatch situation.

Nymph Biology


Current Speed: fast to moderate

Substrate: cobble riffles, rapids, and runs

Rhithrogena nymphs are best known for their unique gills: the first and last pair of gills wrap around the bottom side of the abdomen, creating a "suction cup" which helps them cling to rocks in water even faster than other clingers can tolerate.

They have been portrayed strangely in angling texts, to the extent that they are hard to recognize when first observed in the wild. Many book illustrations show the gills fully spread out and opaque, giving the nymphs an exaggerated ovoid shape. Perhaps because it's hard to draw them any other way in pencil. But this really misrepresents the actual insects; you have to look pretty closely to notice the gill extensions under the body. They are very translucent and easy to miss. In the natural state their transluscent gills are also held much closer to their bodies. These drawings also show short, robust, crab-like body shapes, perhaps to somehow emphasize their proficiency as clingers. This further exacerbates the misconception. They are great clingers, but their bodies are more narrow and streamlined than drawings indicate, as demonstrated in the photos below.

Pictures of 16 Mayfly Specimens in the Genus Rhithrogena:

Specimen Page:123
Female Rhithrogena Mayfly SpinnerFemale Rhithrogena Mayfly Spinner View 9 PicturesI'm very tentatively (see the connected forum thread) sticking this mayfly in Rhithrogena for now.
Collected June 7, 2007 from the West Branch of the Delaware River in New York
Added to Troutnut.com by Troutnut on June 8, 2007
Rhithrogena impersonata (Dark Red Quill) Mayfly NymphRhithrogena impersonata (Dark Red Quill) Mayfly Nymph View 6 PicturesThis was the only Rhithrogena specimen in a large sample of nymphs from a small Catskill stream. It looks virtually identical to Rhithrogena impersonata specimens collected in the Midwest, but I didn't get to check the distinguishing features under a microscope.
Collected April 19, 2006 from Mongaup Creek in New York
Added to Troutnut.com by Troutnut on April 21, 2006
Rhithrogena impersonata (Dark Red Quill) Mayfly NymphRhithrogena impersonata (Dark Red Quill) Mayfly Nymph View 8 PicturesThis specimen shows one of two distinct color types of Rhithrogena impersonata nymphs. This type is very reddish, especially in the gills, and it was formerly in its own species called Rhithrogena sanguinea.
Collected June 5, 2005 from the Long Lake Branch of the White River in Wisconsin
Added to Troutnut.com by Troutnut on May 24, 2006
Specimen Page:123

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