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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 Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
This specimen appears to be of the same species as this one collected in the same spot two months earlier. The identification of both is tentative. This one suffered some physical damage before being photographed, too, so the colors aren't totally natural. I was mostly photographing it to test out some new camera setting idea, which worked really well for a couple of closeups.
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 Ephoron album (White Flies)

Taxonomic History

This species has an interesting history as one of the first American mayflies species to be formally described. The naturalist Thomas Say described it (then as "Baetis alba") as a part of Major Stephen Harriman Long's 1823 expedition to the headwaters of the Mississippi. A narrative of the expedition describes sighting it in abundance in two rivers near the border between Minnesota and Canada, in what is maybe one of the earliest accounts of an American mayfly "superhatch," although sadly wasted on a walleye river:
"Among the objects which chiefly attracted our notice, were the interesting ephemera which we had seen on Winnepeek Winnipeg] River. They became go abundant on Rainy R. toward sunset, that they presented the appearance of a snow storm. They continued for some time, until they were driven by the wind into a small tributary valley where they formed white clouds, beautifully relieved against the
dark green of the forest, deepened in its shade by the approach of night. The ensuing morning their dead bodies were seen floating on the stream, and drifted by the wind into small coves near the shore. From their great abundance, Mr. Say was led to believe that this short-lived insect never witnesses a rising sun, but that after each performance, in a short time, all the duties assigned to it in its perfect state, it deposits its egge and expires in the night, a few hours after it has been evolved from the chrysalis. The next evening the ephemera were again seen very abundantly, but it was evident that this was a new swarm, and not a part of that previously observed." (Keating, 1824).

Where & when

This is the only Ephoron species in the West, where it is known from the large rivers near Yellowstone National Park. It is abundant in the Midwest, and it is present in the East but not to the extent of Ephoron leukon.

In 28 records from GBIF, adults of this species have been collected during July (43%), August (29%), September (21%), and June (7%).

In 31 records from GBIF, this species has been collected at elevations ranging from 618 to 6250 ft, with an average (median) of 3533 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: 11–12 mm

Vertex of head yellowish brown with purplish markings; mesonotum light yellowish brown; veins of costal margin of fore wing purplish grey, all others pale. Face pale yellowish; second basal joint of antenna dusky at apex, filament whitish. Eyes black. Vertex of head yellowish brown, marked and sometimes almost obscured by purplish shading; darkest between ocelli, which are heavily dark-ringed at base. Pronotum yellowish; pleura with purplish grey streaks above leg base. Mesonotum yellow, tinged with yellowish brown on each side of median area; scutellum pale yellowish. Metanotum yellowish brown. Pleura and sternum pale yellowish, the former often tinged with yellowish brown. Fore femur and tibia purplish; femur marked with yellowish white along ventral edge; ventral edge of tibia whitish at extreme base; tarsus smoky grey at base, becoming silvery white apically. Middle and hind legs pale yellowish white. Wings rather semi-hyaline, with faint purplish tinge along the costal border. Longitudinal and cross veins of costal margin purplish grey, cross veins somewhat darker than longitudinals; as far back as the anterior branch of media, the cross veins are faintly greyish; all other veins of both wings colorless. Abdomen pale yellowish white, basal and middle segments often semi-hyaline; apical tergites yellowish. Genitalia pale (see fig. 78). Tails pale smoky at base, becoming whitish apically; joinings opaque whitish.

Discussions of Ephoron album

Polymitarcyidae Question
1 replies
Posted by Steamntrout on Jun 22, 2017
Last reply on Jun 22, 2017 by Crepuscular
What size are these nymphs & Sub Imago's?

Start a Discussion of Ephoron album


Mayfly Species Ephoron album (White Flies)

Species Range
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