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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 alternatus (Gray Drakes)

This species occasionally produces important spinner falls. Its spinners may join the swarms of Siphlonurus quebecensis or Siphlonurus rapidus, amplifying the importance of all three species.

Where & when

Time of year : Early May through early September; peaking from late June through July

In 61 records from GBIF, adults of this species have been collected during July (44%), June (26%), August (23%), and May (7%).

In 285 records from GBIF, this species has been collected at elevations ranging from -30 to 2933 ft, with an average (median) of 689 ft.

Species Range

Spinner behavior

Time of day: Evening

Habitat: Riffles

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: 12 mm

A rather large, somewhat pale species, with conspicuous ventral markings (see fig. 119).

Head whitish. Thorax yellowish brown. Wide reddish brown median stripe on metanotum and lateral margins of mesoscutellum. Scutella dark brown. Pleural sutures brown. Purplish red marks anterior to wing roots. Prosternum white, marked with two dark brown triangles. White band across anterior portion of mesosternum, enclosing a dark median spot.

Fore leg of male longer than body; yellowish. Apical dark band on femur; knee brown; apex of tibia, and tarsal joinings, brown. Femora of middle and hind legs whitish, with apical brown band. Tibiae and tarsi yellowish, joinings brown. Longitudinal veins of fore wing, and costal margin of hind wing, purplish black. Humeral cross vein purplish black. Costal cross veins before bulla pale, almost invisible; in stigmatic area pale brown, numerous, somewhat irregular, a few anastomosed. All other veins brown, the longitudinal veins all pale at the wing root.

Abdomen pinkish white, marked with chestnut brown. Posterior margins of tergites widely banded with brown; wide median brown streak; usual brown triangles and oval spots, the latter very prominent. Pale areas on anterior margin extensive. Tergites 8-10 with large powdery white areas. Ventrally, no lateral patch. Oblique lines extend from near the postero-lateral angle almost to the anterior margin near the median line, ending in a black dot. A pair of smaller black dots near center of each sternite, on each side of median line. A dark brown triangle on median line at the anterior margin. Sternites 7-9 of the female, and 9 of the male, largely yellow with reddish markings. Dark lateral mark on sternite 9 of the male.

Forceps yellowish. Penes yellow tipped with black. Tails reddish brown at the extreme base, becoming yellow and finally white in the distal portion. Joinings rather widely dark purplish brown. Penes as in fig. 123.

Nymph

Nymph has double gills on all abdominal segments, one member of the 7th pair being very small (see 120). Femur with an apical brown band; tibia banded near base; tarsus twice banded. Usual black band across tail, beyond the middle. Ventral markings comparable to those of the imago. This species, originally described from the middle west, is common throughout eastern North America.

Specimens of the Mayfly Species Siphlonurus alternatus

1 Female Spinner
1 Nymph

Start a Discussion of Siphlonurus alternatus

References

Mayfly Species Siphlonurus alternatus (Gray Drakes)

Taxonomy
Species Range
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