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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 Amphizoa (Amphizoidae) Beetle Larva from Sears Creek in Washington
This is the first of it's family I've seen, collected from a tiny, fishless stream in the Cascades. The three species of this genus all live in the Northwest and are predators that primarily eat stonefly nymphs Merritt R.W., Cummins, K.W., and Berg, M.B. (2019).
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 Cinygmula subaequalis (Small Gordon Quills)

This is the only Eastern species of Cinygmula. It may produce fishable hatches in places but it is not a generally important mayfly.

Where & when

Time of year : May and June

Cinygmula subaequalis is widespread but only locally abundant. Caucci and Nastasi in their collections for Hatches II were unable to find any specimens, but Fred Arbona in Mayflies, the Angler, and the Trout mentions consistent subaequalis hatches in the mountains of Pennsylvania, New York, and Vermont.

In 34 records from GBIF, adults of this species have mostly been collected during June (50%), July (24%), May (18%), and August (6%).

In 21 records from GBIF, this species has been collected at elevations ranging from 240 to 2746 ft, with an average (median) of 2280 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: 7 mm
Wing length: 8 mm

Head reddish yellow; “a shining black ring at base of each ocellus, antennae pale” (Bks.). Thorax rather reddish yellow, posterior portion of notum darker. Legs pale, “a black dot at tip of femur and tibia I" (Bks.). Wings hyaline; venation mostly brown, no cross veins dark-margined; stigmatic area brownish yellow. “About five costals before bulla, fourteen beyond, a few near the middle are crossed” (Bks.). Hind wings not dark-margined. Basal joint of fore tarsus of male fully two-thirds as long as second; third equal to second; fourth “‘scarcely longer than first, the fifth not one-third of first.” (Bks.). Abdomen pale; “segments dark on apical one-third or one-half above, last three segments brownish” (Bks.) Forceps pale. Tails faintly dark.

Described as C. atlantica

Body length 7 mm, wing length 8 mm

A rather small pale species; wings not tinted; spines on lower outer margin of penes.

Head yellowish brown; dark brown between eyes. Thorax light brown; lateral areas of pronotum, and postero-lateral areas of mesonota and metanota, shaded with darker brown. Fore legs smoky brown. Middle and hind legs yellowish brown. Wings hyaline, not tinted; all veins fine, brown. Abdominal tergites 2-6 semi-hyaline, pale, with brown shading laterally. Tergites 2 and 3 pale in central median area only; tergites 4 to 6 largely pale, the brown shading restricted to postero-lateral areas. Submedian pale dashes, partially outlined in brown, are faintly indicated. Sternites pale ochreous, 2-6 semi-hyaline, 7-9 opaque. Tergites 7-10 opaque, almost wholly brown. Tails pale brown; penes smoky brown. A spine is present on lower outer margin of penes on each side, but none in inner margin (see fig. 103).

This species is allied to Cinygmula par, by the structure of the genitalia, but it lacks the inner spine on the penes found in that species. The paler abdominal tergites and lack of mid-ventral dark markings in C. atlantica serve to distinguish it from C. par.

Specimens of the Mayfly Species Cinygmula subaequalis

2 Nymphs

Start a Discussion of Cinygmula subaequalis


Mayfly Species Cinygmula subaequalis (Small Gordon Quills)

Species Range
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