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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Dorsal view of a Sweltsa (Chloroperlidae) (Sallfly) Stonefly Nymph from the Yakima River in Washington
This species was fairly abundant in a February sample of the upper Yakima.
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 Ephemerella tibialis (Little Western Dark Hendricksons)

Ehhemerella tibialis (Little Western Red Quill, Little Western Dark Hendrickson) is a common western species that can be very important at times. It is perhaps also one of the most confusing species. Unlike it's western generic counterparts the species is described as dark and their females produce dark eggs. Until recently, it was classified in the Serratella genus with species that share these traits. Regardless, it is the only small, dark ephemerellid the western angler is likely to find important. Favorite patterns used for size 18 Pale Morning Dun hatches tied in eastern Dark Hendrickson colors should be the ticket.

As with many of it's sister species it is widely adaptable and may be variable in its appearance. Scientific literature and many angling sources describe it as a small dark mayfly. Not everybody agrees. Ralph Cutter, West Coast author of several angler/entomology books and articles describes it in Sierra Trout Guide as a much larger pale mayfly and dubs it the Creamy Orange Dun. He also mentions the nymph as being easy to recognize by the faint dorsal stripe running down its back and its often fiery brownish red color. These descriptions also match a variation of the ubiquitous and common Ephemerella excrucians.

Where & when

Time of year : August to September

Altitude: Medium to high

Known distribution covers all the mountainous regions of the West excepting the California Coast. It is especially adaptable to many habitats.

In 12 records from GBIF, adults of this species have been collected during July (58%), August (25%), and June (17%).

In 27 records from GBIF, this species has been collected at elevations ranging from 95 to 9500 ft, with an average (median) of 7835 ft.

Species Range

Hatching behavior

Time of day : Midday

Spinner behavior

This is the only spinner (imago) in the genus with dark blackish eggs. General consensus is these spinner falls are rarely important to the angler.

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.

Nymph

Body length: 7-8 mm

A slender species probably allied to the Ephemerella needhami group; only the nymph is known; lateral extensions of the abdomen inconspicuous; dorsal spines present.

Head and thorax smooth. Maxillary palp weak but perfect in form. Antennae pale. General color pale reddish brown. Wing pads and the mesonotum anterior to them dark brown in mature nymphs. Legs pale, with no conspicuous markings. 6 to 7 denticles on each claw. Hind leg rather long.

Abdomen relatively long and slender; middle segments slightly wider than the basal and apical ones. Lateral extensions inconspicuous. Postero-lateral spines on segments 4-9. Gills borne on segments 3-7. Dorsal spines present on tergites 2-8; short and inconspicuous on 2 and 3, well developed on 5-7. Anterior margin of each tergite pale. Posterior margin often narrowly dark brown; remainder reddish brown. Rather large lateral patches may be present next to the gills on the middle segments. No definite ventral markings. Tails pale, almost bare at base and tip, and with only a few short spines in the middle area; in mature nymphs, with narrow dark half-rings at the base

Male Spinner

Body length: 7.5 mm
Wing length: 8 mm

A member of the serrata group (now a synonym of Serratella serrata); abdominal segments of male translucent whitish on the anterior margins; tails deep smoky; fore tibia twice as long as the femur.

General color of male imago deep purplish brown. Thorax almost blackish dorsally. Fore femur pale smoky yellowish, tibia deep smoky, tarsus paler than the tibia; tibia fully twice as long as the femur. Middle and hind legs dull yellowish, the femora with reddish bands apically. Wings vitreous; venation pale grey-brown, the cross veins rather more distinct than is usual for this group. Anterior margins of abdominal segments 3-8 narrowly whitish, translucent. Sternites with indications of dark ganglionic blotches. Forceps reddish basally, blackish distally. Penes blackish (see fig. 156). Tails deep smoky, slightly darker at the joinings.

Specimens of the Mayfly Species Ephemerella tibialis

1 Male Dun
2 Female Duns
3 Nymphs

Discussions of Ephemerella tibialis


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References

Mayfly Species Ephemerella tibialis (Little Western Dark Hendricksons)

Taxonomy
Species Range
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