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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.

Case view of a Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
It's only barely visible in one of my pictures, but I confirmed under the microscope that this one has a prosternal horn and the antennae are mid-way between the eyes and front of the head capsule.

I'm calling this one Pycnopsyche, but it's a bit perplexing. It seems to key definitively to at least Couplet 8 of the Key to Genera of Limnephilidae Larvae. That narrows it down to three genera, and the case seems wrong for the other two. The case looks right for Pycnopsyche, and it fits one of the key characteristics: "Abdominal sternum II without chloride epithelium and abdominal segment IX with only single seta on each side of dorsal sclerite." However, the characteristic "metanotal sa1 sclerites not fused, although often contiguous" does not seem to fit well. Those sclerites sure look fused to me, although I can make out a thin groove in the touching halves in the anterior half under the microscope. Perhaps this is a regional variation.

The only species of Pycnopsyche documented in Washington state is Pycnopsyche guttifera, and the colors and markings around the head of this specimen seem to match very well a specimen of that species from Massachusetts on Bugguide. So I am placing it in that species for now.

Whatever species this is, I photographed another specimen of seemingly the same species from the same spot a couple months later.
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 Ameletus ludens (Brown Duns)

This mayfly, which occasionally produces fishable hatches, is interesting because it's one of the only mayflies capable of parthenogenesis.

Where & when

Time of year : Late spring

Preferred waters: Freestone streams

This is the most important Eastern species of Ameletus.

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

Species Range

Hatching behavior

Time of day : Late afternoon

Fred Arbona notes in Mayflies, the Angler, and the Trout that the best Ameletus ludens hatches come on cloudy days.

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: 8.5 mm
Wing length: 9 mm

A rather small clear-winged brownish species, with distinct blackish oval ganglionic marks on the venter of the abdomen.

Head of male blackish. Eyes of male honey-colored in life. Thorax reddish brown. Mesonotum yellowish to olive brown; scutellum reddish yellow; the area just anterior to it cream colored, and a pale cream colored patch on each lateral margin. Metanotal scutellum rather similarly marked. Anterior to the wing root is a pale cream colored area varied with a reddish tinge; similar patches on the pleura. Sternum blackish in the male. Fore legs dark reddish brown; middle and hind legs brown. Wings hyaline, veins blackish brown. Stigmatic cross veins tend to anastomose. Abdomen of male semi-translucent except on the apical segments; pale yellowish brown above, paler beneath. Basal and apical segments washed with reddish brown. Rather wide dark brown bands on the posterior margins; postero-lateral angles dark brown. Sternites paler than tergites; apical sternites opaque reddish brown. Each ganglionic area is marked by a blackish oval spot, having a distinct black line through the center. Posterior margins, behind the dark bands, narrowly pale. Margin of pleural fold pale. Apical tergites and sternites often marked with creamy white areas which are tinged with red. Basal sternites pale, semi-translucent; apical sternite opaque. Forceps blackish, tawny at the base. The long joint of the forceps is swollen basally and distally. The penes are long and slender, slightly divergent distally (see fig. 116). Tails dark reddish brown basally, becoming somewhat paler distally. Joinings darker.

Female Spinner

Body length: 8.5 mm
Wing length: 9 mm

Head of female dark brown. Pronotum with paler median and lateral areas. Sternum dark reddish brown. Abdomen reddish brown dorsally, paler ventrally. The subanal plate of the female is rather long, extending almost to the end of the tenth segment.

Nymph

The mature nymph is dark reddish brown with cream colored markings. Legs pale, banded with brown. Abdominal tergites 8-10 very dark brown; basal and middle tergites varied with indistinct paler median, lateral and posterior markings. Dark brown oblique submedian marks present. Postero-lateral spines on segments 4-9, very small on 4 and 5. Ventrally, three very wide dark reddish brown bands occupy most of each sternite. These bands coalesce completely on sternites 8 and 9, and are more or less diffuse on the other sternites. No distinct pale streak separates the lateral dark line from the lateral margin of the sternite. Tails with the usual dark bands. This species is of particular interest in that it ordinarily reproduces parthenogenetically.

Specimens of the Mayfly Species Ameletus ludens

3 Nymphs

Discussions of Ameletus ludens

Brown Dun hatch/swarm time?
10 replies
Posted by Konchu on Apr 25, 2009
Last reply on Apr 29, 2009 by Troutnut
Has anyone else watched a Brown Dun hatch or swarm? If so, what time of day did you see it, and how long did it last?

I came upon a woodland swarm late this evening. I thought I saw mating occurring higher above the stream. This would mean that parthenogenesis is not necessarily happening in "my" stream. I watched for awhile, but got distracted (venomous snake). I hope to catch it (the hatch, not the snake) again tomorrow night and note the egg-laying behavior and possibly nab some male adults for science. There's a range of nymph ages, so I should be OK, weather permitting.

Start a Discussion of Ameletus ludens

References

Mayfly Species Ameletus ludens (Brown Duns)

Taxonomy
Species Range
Common Name
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