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.
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This one was surprisingly straightforward to identify. The lack of a sclerite at the base of the lateral hump narrows the field quite a bit, and the other options followed fairly obvious characteristics to Clostoeca, which only has one species, Clostoeca disjuncta.
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Mayfly Genus Epeorus (Little Maryatts)
There is remarkable variety of form and color within this prolific genus of fast-water mayflies. Different species are found across the country, and several cause good hatches. Fly anglers are likely to encounter the lesser species on occasion, too.
The best Epeorus hatch in the East is Epeorus pleuralis, the famous Quill Gordon, the first abundant large mayfly hatch of the year. Epeorus vitreus comes a little later and is important in both the East and Midwest.
In the West, Epeorus longimanus dominates in fast, high-altitude streams, while Epeorus albertae inhabits slower and lower waters.
The best Epeorus hatch in the East is Epeorus pleuralis, the famous Quill Gordon, the first abundant large mayfly hatch of the year. Epeorus vitreus comes a little later and is important in both the East and Midwest.
In the West, Epeorus longimanus dominates in fast, high-altitude streams, while Epeorus albertae inhabits slower and lower waters.
Genus Range
Hatching behavior
All Epeorus duns emerge from their nymphal shucks below the surface, often while still attached to the stream bed. Most species (with the exception of Epeorus pleuralis) take to the air quickly after emerging. These two factors make wet emerger patterns especially effective during Epeorus hatches.Nymph biology
Most Epeorus species require fast, pure water flowing over gravel or boulders. Some can inhabit moderate currents.Specimens of the Mayfly Genus Epeorus
10 Male Duns
Identification of this one was as follows. Body 9 mm, wing 11 mm.
Both Epeorus albertae and Epeorus dulciana should have a conspicuously darkened humeral crossvein in the forewing. This one doesn't.
The foretarsal claws are dissimilar (one sharp, one blunt), which also rules out the Epeorus albertae group.
The dark macula on the forefemora rules out Epeorus deceptivus, which is also supposed to be a little bit smaller.
Both Epeorus grandis and Epeorus permagnus should be much, much larger.
Of the species known to be present in Washington, this leaves only Epeorus longimanus, which is exactly the right size. The key to male spinners in Traver (1935) describes distinctive markings that are visible (although more faintly) in this dun: “Black posterior margins of tergites do not extend laterally to pleural fold, but an oblique black line form this margin cuts across poster-lateral triangle to pleural fold.”
Both Epeorus albertae and Epeorus dulciana should have a conspicuously darkened humeral crossvein in the forewing. This one doesn't.
The foretarsal claws are dissimilar (one sharp, one blunt), which also rules out the Epeorus albertae group.
The dark macula on the forefemora rules out Epeorus deceptivus, which is also supposed to be a little bit smaller.
Both Epeorus grandis and Epeorus permagnus should be much, much larger.
Of the species known to be present in Washington, this leaves only Epeorus longimanus, which is exactly the right size. The key to male spinners in Traver (1935) describes distinctive markings that are visible (although more faintly) in this dun: “Black posterior margins of tergites do not extend laterally to pleural fold, but an oblique black line form this margin cuts across poster-lateral triangle to pleural fold.”
The lack of a darkened humeral crossvein rules out Epeorus albertae and Epeorus dulciana. The lack of a dark macula on the forefemora rules out Epeorus longimanus. The small size rules out Epeorus grandis and Epeorus permagnus. That leaves as the only possibility known in Washington state Epeorus deceptivus. It is a small species, although not reportedly quite as small as this specimen. I couldn't find anything in the species description in Traver (1935) to definitively confirm or rule out the species ID, given that I don't have the preserved specimen to check under a microscope, but it has to be either deceptivus or something not yet reported in Washington.
It was collected at the same time as a similar-sized female dun.
It was collected at the same time as a similar-sized female dun.
I collected this male dun with a female dun and a female spinner of the same species. Identification was initially difficult because I didn't catch a male spinner, and this dun was missing its legs. I was able to tease the spinner's penes out of the dun's shuck after it expired, although the shape was pretty similar. Fortunately, the shape is a distinctive match to the Epeorus albertae species group. In the key in Needham et al (1935), it keys to Epeorus youngi, which is now considered a synonym of albertae. It's also a very plausible dun version of this spinner collected a few years earlier, a few drainages to the north, at a similar time of year. Additionally, the female dun and spinner collected with this one match very closely those I've collected in the past.
I kept this specimen after photographing it and it molted into a spinner in perfect condition, which I photographed here.
This Epeorus dun managed to emerge successfully even though it had apparently long several legs at some point and only partially grown them back.
This is my favorite mayfly from 2004, and it appears on my popular Be the Trout: Eat Mayflies products. Check them out!
Its identification is really up in the air. It might be a late-season vitreus dun but it may very well be one of the more obscure species in that genus.
Its identification is really up in the air. It might be a late-season vitreus dun but it may very well be one of the more obscure species in that genus.
I collected this male dun together with a female spinner, a female dun, and another male dun. I photographed this bedraggled one, larger than the other male, to show some of the greatest size variation within the species.
8 Female Duns
I collected this female dun with a male dun and a female spinner of the same species.
This dun comes from the same location, and is about the same size, so is presumably the same species as this male spinner.
I collected this female dun together with a female spinner, a male dun, and a larger, damaged male dun.
I'm guessing this female is of the same species as this male dun, because they came from the same pool at the same time and the size matches, although the males and females would look very different in this case.
11 Male Spinners
This spinner appeared inside our car after a rest stop overlooking the Snake, so that's most likely where it came from. Two different keys place it firmly in Epeorus albertae.
I spent most of the day looking for Epeorus pluralis duns or spinners without any luck on the major Catskill rivers. Finally in the evening I arrived at a small stream somebody had recommended, and when I got out of the car I was happy to find that I had parked in the middle of a cloud of male spinners.
I collected a female dun on the same day that probably belongs to the same species as this spinner. It keys pretty clearly to Epeorus pleuralis among the species given in the key in Taxonomy of Epeorus Frisoni (burks) And a Key to New England Species Of Epeorus.
This spinner and hundreds of others like it were dancing over the road through a very narrow valley carved by a tiny, steep tributary of the trout stream I was fishing. I got strange looks from a few passers-by, standing around on the road with a butterfly net...
A few days earlier I photographed this same specimen as a dun. The changes between dun and spinner seem particularly dramatic in this species.
10 Female Spinners
I collected this female spinner with a male dun and a female dun of the same species.
I collected this one as a dun, and she molted into a spinner in my room.
I associated this female with a male I collected one night later. For a great and informative discussion of all Epeorus species and other mayflies be sure and read, WESTERN MAYFLY HATCHES by R. Hafele and D. Hughes. They rate all of the western mayflies and they rate the hatch of this genus a 25 out of a possible 45 points based on several rating criterion. They provide insect photos, possible fly patterns and fly presentations. This is a great book.
Edit by Troutnut: Bob generally knows his IDs better than I do, but I think this one was misidentified as Epeorus longimanus. The darkened humeral crossvein is not supposed to be present in longimanus. I'm moving it up to Epeorus.
Edit by Troutnut: Bob generally knows his IDs better than I do, but I think this one was misidentified as Epeorus longimanus. The darkened humeral crossvein is not supposed to be present in longimanus. I'm moving it up to Epeorus.
It is hard to see where the name "Pink Lady" comes from.
19 Nymphs
This specimen keys to the Epeorus albertae group of species. Of the five species in that group, the two known in Washington state are Epeorus albertae and Epeorus dulciana. Of the two, albertae has been collected in vastly more locations in Washington than dulciana, suggesting it is far more common. On that basis alone I'm tentatively putting this nymph in albertae, with the large caveat that there's no real information to rule out dulciana.
Identification notes from the microscope: Gills on segment 1 extend anteriorly below the body, but not all the way to touching; posterolateral spines minor; femora without fuscous macula.
Gills #1 failing to meet at the center sterna combined with a lack of small dark single spots mid-femur are characters that differentiate Epeorus deceptivus from Epeorus longimanus.
Key features I discerned with a microscope include that the femoral flange is blunt (again, given the other features and location, I probably misread this one), postero-lateral spines with the anterior longer, and the first gill is not extended.
Key features I discerned with a microscope include that the femoral flange is blunt (later note: on nymphs of this size, it's somewhat ambiguous and the femora can be damaged in the collection process), the postero-lateral spines have a longer anterior, the first gill is not extended, all gills are tracheated, and the femora have a distinctive brown spot on the center while all the other spots are gray.
I suspect this is an Epeorus vitreus nymph. At the current instar, it's tough to make out the pair of dots on the tergites which signify that species, but with zooming and contrast enhancement they become evident.
3 Streamside Pictures of Epeorus Mayflies:
9 Underwater Pictures of Epeorus Mayflies:
In this picture: Mayfly Genus Epeorus (Little Maryatt) and Mayfly Family Baetidae (Blue-Winged Olive).
In this picture: Mayfly Genus Epeorus (Little Maryatt) and Mayfly Family Baetidae (Blue-Winged Olive).
In this picture: Mayfly Genus Epeorus (Little Maryatt) and Animal Class Gastropoda (Snail).
There are a couple Epeorus mayfly nymphs clinging to this rock. One interesting thing I've noticed is that even though the stream has a lot of clingers, they rarely show up in my photos, and I've started paying more attention to the river bottom while I'm fishing I've noticed that clinger nymphs generally see or feel me coming and scurry to the undersides of their rocks before I can get in picture range. I think I have the same problem with stoneflies.
In this picture: Mayfly Genus Epeorus (Little Maryatt).
This is a pretty clear photo of an Epeorus nymph clinging flat against a log. The big mound of debris on the bottom center of the picture, attached to the light rock, is a structure that's been puzzling me. I've found several in one section of the river. It's big, like 2 inches long and maybe 1/2-3/4 inch wide/tall, and hollow, like some sort of coccoon or something. It's clearly a structure built by some sort of little creature, but I'm not sure what.
In this picture: Mayfly Genus Epeorus (Little Maryatt).
This log houses several Ephemerella mayfly nymphs and, on the top right, an Epeorus mayfly nymph.
In this picture: Mayfly Species Ephemerella invaria (Sulphur) and Mayfly Genus Epeorus (Little Maryatt).
Discussions of Epeorus
Distance between the eyes of male Epeorus
Posted by Troutnut on May 3, 2007
Last reply on May 3, 2007 by Troutnut
There has been some discussion here before about Epeorus identification, especially the distance between the eyes of the adult males, which is one identifying characteristic. The keys say that the distance should be "less than the width of the median ocellus," but I have collected a few male duns that didn't quite fit that requirement.
We figured they were Epeorus anyway, so it's not a big deal, but a new specimen I collected sheds a bit of light on the question.
I collected a dun whose eyes were also a bit far apart, which you can see here:
http://www.troutnut.com/specimen/681
Then it molted into a spinner:
http://www.troutnut.com/specimen/682
The spinner's eyes were really almost touching, well within the description of the genus. So that answers our question: the duns may have a little wider spread and the gap will close up in the spinners.
We figured they were Epeorus anyway, so it's not a big deal, but a new specimen I collected sheds a bit of light on the question.
I collected a dun whose eyes were also a bit far apart, which you can see here:
http://www.troutnut.com/specimen/681
Then it molted into a spinner:
http://www.troutnut.com/specimen/682
The spinner's eyes were really almost touching, well within the description of the genus. So that answers our question: the duns may have a little wider spread and the gap will close up in the spinners.
Synonym of vitreus
3 replies
Start a Discussion of Epeorus
References
- Arbona, Fred Jr. 1989. Mayflies, the Angler, and the Trout. Nick Lyons Books.
- Burian, Steven K., Swartz, Beth I., Wick, Philip C. 2008. Taxonomy of Epeorus Frisoni (burks) And a Key to New England Species Of Epeorus. International Advances in the Ecology, Zoogeography, and Systematics of Mayflies and Stoneflies undef(undef): 276-294.
- Caucci, Al and Nastasi, Bob. 2004. Hatches II. The Lyons Press.
- Knopp, Malcolm and Robert Cormier. 1997. Mayflies: An Angler's Study of Trout Water Ephemeroptera . The Lyons Press.
- Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.
Mayfly Genus Epeorus (Little Maryatts)
Taxonomy
Species in Epeorus
Epeorus albertaePink Ladies
13
74
Epeorus deceptivus
4
29
Epeorus dispar
0
0
Epeorus dulciana
0
0
Epeorus fragilis
0
0
Epeorus frisoni
4
26
Epeorus grandis
3
20
Epeorus hesperus
0
0
Epeorus lagunitas
0
0
Epeorus longimanusSlate Brown Duns
5
29
Epeorus permagnus
0
0
Epeorus pleuralisQuill Gordons
8
71
Epeorus punctatus
0
0
Epeorus suffusus
0
0
Epeorus vitreusSulphurs
15
64
Species in Epeorus: Epeorus albertae, Epeorus deceptivus, Epeorus dispar, Epeorus dulciana, Epeorus fragilis, Epeorus frisoni, Epeorus grandis, Epeorus hesperus, Epeorus lagunitas, Epeorus longimanus, Epeorus permagnus, Epeorus pleuralis, Epeorus punctatus, Epeorus suffusus, Epeorus vitreus
4 species (Epeorus margarita, Epeorus metlacensis, Epeorus namatus, and Epeorus subpallidus) aren't included.