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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
Baetis

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 Neoleptophlebia (Leptophlebiidae) Mayfly Nymph from the Yakima River in Washington
Some characteristics from the microscope images for the tentative species id: The postero-lateral projections are found only on segment 9, not segment 8. Based on the key in Jacobus et al. (2014), it appears to key to Neoleptophlebia adoptiva or Neoleptophlebia heteronea, same as this specimen with pretty different abdominal markings. However, distinguishing between those calls for comparing the lengths of the second and third segment of the labial palp, and this one (like the other one) only seems to have two segments. So I'm stuck on them both. It's likely that the fact that they're immature nymphs stymies identification in some important way.
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 Siphlonurus columbianus (Gray Drakes)

Where & when

According to Fred Arbona in Mayflies, the Angler, and the Trout, this species is abundant and widespread across the West and as far east as South Dakota. The USGS distribution records do not reflect this, but they are often incomplete.

In 3 records from GBIF, adults of this species have been collected during July (67%) and June (33%).

In 3 records from GBIF, this species has been collected at elevations of 2000, 3500, and 5971 ft.

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: 12 mm
Wing length: 13 mm

A large species, much resembling Siphlonurus occidentalis in its general appearance.

Head brown. Thorax deep brown. Mesothoracic scutellum blackish, with a paler ruddy spot directly anterior to it. Pleural sutures and wing bases yellowish. Fore legs deep blackish brown; middle and hind legs light yellowish brown. Femora marked with a slight purplish brown streak before the apex; tarsal joinings also purplish brown. Wings hyaline, with a faint brownish tinge in the stigmatic area. Veins entirely blackish.

Abdomen deep purplish brown dorsally, the pale anterior triangles light yellowish. Ventrally dull yellowish. The broad purplish brown oblique streaks are usually united on the anterior margin to form the blackish U-shaped marks. These are less distinct than in occidentalis, especially on sternites 8 and 9, where they barely join, are diffuse and poorly defined. Two tiny dark dots are usually present near the center of each sternite, within the dark U-mark. Segment 10 is wholly brown. Forceps dark with paler base. Penes as in fig. 122. Tails dark at base, becoming paler distally. Joinings brown.


Start a Discussion of Siphlonurus columbianus

References

Mayfly Species Siphlonurus columbianus (Gray Drakes)

Taxonomy
Species Range
Common Names
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