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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Dorsal view of a Holocentropus (Polycentropodidae) Caddisfly Larva from the Yakima River in Washington
This one seems to tentatively key to Holocentropus, although I can't make out the anal spines in Couplet 7 of the Key to Genera of Polycentropodidae Larvae nor the dark bands in Couplet 4 of the Key to Genera of Polycentropodidae Larvae, making me wonder if I went wrong somewhere in keying it out. I don't see where that could have happened, though. It might also be that it's a very immature larva and doesn't possess all the identifying characteristics in the key yet. If Holocentropus is correct, then Holocentropus flavus and Holocentropus interruptus are the two likely possibilities based on range, but I was not able to find a description of their larvae.
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 impersonata (Dark Red Quills)

This intriguing species has two distinct colors of nymphs, which were once considered to be different species. Most nymphs are a dark olive gray, but some are a surprisingly bright reddish brown. The red ones were once classified as Rhithrogena sanguinea. There is no apparent difference between the adults of the two varieties.

Where & when

Time of year : Late May through early July

I have not found any discussion of fishable hatches of this species, but I have sampled two small streams where the nymph population is so dense that there must be good fishing to the adults unless they have the worst of emergence characteristics.

In 26 records from GBIF, adults of this species have mostly been collected during June (54%), July (15%), May (15%), and August (8%).

Species Range

Hatching behavior

Spinner behavior

Time of day: Dusk

The Leonards write in Mayflies of Michigan Trout Streams that the spinners gather in great swarms high above the river as the sun sets. They do not say whether this activity culminates in a fishable spinner fall.

Nymph biology

Current speed: Fast

Substrate: Gravel

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: 9 mm
Wing length: 10 mm

A species of the jejuna-undulata group, having no lateral spine basally on penes; small apical spines present on each division of penes.

Head and thorax deep brown; thoracic sternum paler, rather ochreous brown. Legs ochreous brown; femora “‘broadly shaded in their central portion with deeper brown, especially noticeable on the forelegs’” (McD.). Wings hyaline; a slight brownish tinge at base. Venation strong, blackish. Abdominal tergites deep brown; sternites paler, ochreous brown. Forceps and tails dark brown. Penes with no lateral basal spines on outer margin; apices “broader and much less outcurved” (McD.) than in the allied Rhithrogena jejuna, each division bearing several small apical spines (see fig. 101).

Distinguished from R. jejuna and Rhithrogena undulata by the small apical spines on penes, and by the fact that the penes are barely or not at all outcurved at tips.

Specimens of the Mayfly Species Rhithrogena impersonata

3 Nymphs

Start a Discussion of Rhithrogena impersonata


Mayfly Species Rhithrogena impersonata (Dark Red Quills)

Species Range
Common Names
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