Mayfly Family Heptageniidae (March Browns, Cahills, Quill Gordons)

For details about the tentative identification of this male dun, see the page for associated male spinner, captured from a mating swarm in the same location and at the same time as this dun was emerging.

This pretty little dun was part of a sparse midsummer evening hatch on a large Catskill river.

I could not identify it by following a species key step by step, but I tentatively keyed it to the genus Nixe, and based on distribution maps and physical descriptions the most likely species is Nixe inconspicua. (Edit in 2023: this species was recently moved from Nixe into Afghanurus.)

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.

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.

This dun emerged from a nymph in one of the bowls on my table while I was sorting. I photographed it with the nymphal shuck, and it seems to be of the same species as a nymph I photographed from the same sample.

I kept this specimen after photographing it and it molted into a spinner in perfect condition, which I photographed here.

I collected this male dun together with a female spinner, a female dun, and another male dun.

I collected this mayfly on the same trip as a female of the same species. After these photos it molted into a spinner. This is the form of Stenonema vicarium which anglers call the "Gray Fox."

This dun hatched out from a nymph in my aquarium on July 16th, after being collected July 10th. It is probably of the same species as this nymph, and this dun which also hatched from one of these seemingly identical nymphs.

This Epeorus dun managed to emerge successfully even though it had apparently long several legs at some point and only partially grown them back.

I collected this male dun together with a female.

I collected this female dun with a male dun and a female spinner of the same species.

I was surprised by the olive cast on the body of this female Rhithrogena dun, which led me to mistake it for a western green drake (Drunella) in the field. I was pleasantly surprised to get a closer look and find something I hadn't collected yet. Its species ID is based on proximity to male spinner collected on the same trip, as well as physical similarity (size, tergite coloration, dark streaks on the femora) to that specimen.

I'm calling this one Cinygmula just based on the general look and the fact that the genus is very common in this river. Official keys can't rule out other Heptageniidae, though.

I'm guessing this one is Rhithrogena virilis based on collection of a male spinner of similar size and body configuration during the same trip.

This female looks very much like a male I collected a few hundred miles away a few days later, so I'm guessing it's the same species, which I believe is Maccaffertium mediopunctatum.

Here's a classic March Brown dun from the Catskills.

This female dun emerged from a creek loaded with mature Cinygmula nymphs including this specimen, so they're probably the same species. Unfortunately there aren't species keys for either stage.

This dun is almost certainly of the same species as this nymph, as it hatched in my cooler from a nearly identical nymph.

This dun comes from the same location, and is about the same size, so is presumably the same species as this male spinner.

I found this dun on the same piece of stream as a similar spinner, probably of the same species.

The identification of this specimen is not positive because some of the key characteristics conflict. The uniform amber tint of the wings and the rusty-colored mid-ventral markings on some of the abdominal sternites point to Cinygmula uniformis, but I could not locate the small ventral subapical spines on the penes that are supposed to also diagnose that species (the ones visible in the pictures aren't the ones I'm talking about). If I prioritize that characteristics, this would probably be Cinygmula mimus, but then the wing and sternite shading/markings are wrong.

This specimen was one of several males fluttering around over the river late in the afternoon near the Twin Falls trailhead on May 14. It's pretty clearly the same species as this one collected on June 22 five years earlier.

I also collected a nymph of presumably the same species in the riffle beneath these dancing males.

This one was very puzzling to identify. It's clearly Heptageniidae. It keys pretty easily to couplet 58 in Merritt, Cummins, & Berg 5th Edition, but that's where things get tricky.

58: Male penes distinctly L-shaped; Segment 1 of foretarsi usually 1/3 to 2/3 the length of segment 2
58': Males penes not distinctly L-shaped; Segment 1 of foretarsi usually 1/5 to 1/2 the length of segment 2

The characteristics conflict here, as I'd say the penes ARE L-shaped, but the fore tarsal ratio is less than 1/3. Maybe the weasel word "usually" allows for that, and it's some kind of Stenonema, for which I'm not aware of any records in Montana, let alone western Montana.

Going by the tarsal ratio and assuming it's not Stenonema, everything in couplet 60 points to Afghanurus: contiguous compound eyes, genitalia similar to fig 13.222 in MC&B, and weakly developed basal costal crossveins in the forewings. But I looked up the original descriptions of the three Afghanurus species, and the body sizes (flowersi 5-7 mm, inconspicua 4 mm, joernensis 6-7 mm) are way below this one's 10 mm.

This led me to notice that the closely related Ecdyonurus is not included in the key at all, so I checked the descriptions of those species and found that Ecdyonurus criddlei fits very well: the color of the legs, the markings on the tergites and sternites, the short fore tarsus and ratios of the segments, etc. It was originally described as 7 mm, smaller than the 10 mm body of this specimen, but synonyms have been described with larger sizes including wing lengths up to 11 mm for females for Heptagenia salvini.

This specimen was found with a female nearby, which I think is probably the same species, although it is difficult to be certain.

I collected numerous spinners from a thick dusk mating swarm and spinner fall over the Cedar River on a cloudy evening at the end of June. Duns were emerging at the same time, so I was able to collect several male spinners as well as a female spinner, a male dun, and a female dun of the same species, whatever it is. The microscope pictures here come from a mix of those different males, but all the macro DSLR photos are of the same individual.

This one is difficult to identify, though I went into a lot of detail since I caught so many and their fall really got the fish rising for a while at dusk. The penes have a single set of lateral subapical spines, and the wings of the male spinner appear to be untinted, although there may be a barely-perceptible uniform yellow tint. The two claws at the end of each tarsus are similar to each other in shape. The wing is 7.5 mm long and the body is 7 mm long.

I think these are the possibilities:

1. The best guess is Cinygmula tarda, which is the only species matching the size of this specimen in Needham et al (1935). The rest of the description seems to fit pretty well. However, the picture of the genitalia in that source and the one Slater & Kondratieff (2004) differ somewhat from each other and from this specimen, which more closely fits the drawing for Cinygmula mimus.

2. My next guess would be Cinygmula tioga. The original description in Mayo (1952) fits remarkably well, and it's only reported to be 1 mm longer than this specimen (within the likely range of natural variation). It hasn't been reported yet from Washington, only California and Oregon, but the sites in north-central Oregon aren't implausibly far from west-central Washington. However, the drawing of the penes suggests that the lateral spine should be longer or located closer to the tip than in this specimen, and that species is also supposed to have yellow-tinged wings. There may be a very faint tinge to this specimen, but it's hard to tell.

3. It could be either a species not yet described or an undescribed variant of a current species.

And here's a quick list of why other local species were ruled out:

mimus — This species is the best match for the genitalia, but it's supposed to be much larger with a wing length of 10-11.5 mm, and it should have clearer tinting to the wings in a particular pattern. However, Mayo (1952) notes that mimus should not have tracheations on the tergites, as this one clearly does, which would make it fit tioga. I'm not sure where tarda falls on that characteristic. Also, Slater & Kondratieff (2004) describe the compound eyes of mimus as contiguous, which doesn't fit this specimen. This specimen also has dark mid-ventral markings on the sternites, which mimus should lack.
uniformis — wing length 10 mm, small ventral subapical spine on penes not present in this specimen,
reticulata — wing length 9 mm, has distinctive wing patterning definitely not present on this specimen.
par — wing length 9-10 mm, penes lack prominent lateral spines, generally shaped wrong, tarsal claws would be dissimilar in par
ramaleyi — wing length 10 mm, penes shape way off
gartrelli — wing length 10 mm, crossveins in costal half of forewing margined with brown (unlike this specimen), penes shape similar being in same group with mimus, but has an extra small spine not present in this specimen

This male was collected at the same time as this female and is likely the same species.

It keys pretty clearly to Rhithrogena undulata using the key in Traver 1935, although the size is larger than expected for that species in that source.

This male was collected from the same cloud of spinners as this female and is probably the same species. I'm tentatively calling them both Cinygmula for now, but I'm really not sure about that ID yet.

I'm fairly sure this is a specimen of Rhithrogena virilis based on closeup examination of the reproductive anatomy under the microscope (not shown in photos). The other other species of Rhithrogena this large is Rhithrogena flavianula, but the key in Needham's Biology of Mayflies mentions annulation in the abdomen (visible in some images on bugguide.net) more distinct than that on this specimen.

The body and front wing were both about 15.5 mm long, while the cerci were 40 mm long.

A couple days earlier I caught a male spinner of this species with some wing damage and missing tails, so I went back to the same pool try to get one more intact. This one has some leg damage, but between the two specimens you can get an idea what the whole insect looked like. There were small clouds of Cinygma dimicki spinners again over the same two small, specific locations in the pool, which is an interesting testament to how repeatably they choose their ideal mating habitat. I was able to capture this one and a female.

I only caught a couple of these, and they were both females, so I'm not sure I'll be able to identify it any further.

This one was collected close to a male which, based on size and general structure, was likely the same species. Females are supposed to be lighter-colored and with less distinct markings than the males, although the difference in this pair is particularly stark.

This female spinner was collected with a male from the same swarm.

Although I couldn't key out this female spinner, I'm fairly comfortable calling her Stenonema modestum based on the markings on the abdomen and their similarity to those on the males of this species. This one probably came from the Namekagon River, although there's a possibility it came from the West Fork of the Chippewa River, because it was found in the truck after fishing those streams on back-to-back days.

This one was collected at the same time as this male and is likely the same species.

This female was collected from the same spinner cloud as this male.

For details about the tentative identification of this female spinner, see the page for associated male spinner, captured from the same mating swarm.

I was able to identify this female because I captured her while she was mating with an identifiable male.

This one may look a bit strange, because one of her main wings came off in my container.

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.

This nymph was one of several mature Cinygmula nymphs collected at the same time as this female dun emerged, so they're probably the same species. Unfortunately there aren't species keys for either stage.

Unfortunately there's no good key to species of Cinygmula nymphs and I didn't find an adult, so this one will have to stay at genus level.

I'm basing the ID of this near-mature nymph on a male spinner with similar size and markings, collected on the same trip. There isn't a key to reliably identify the nymphs of most Rhithrogena species otherwise.

This specimen seems to be of the same species as a dun I photographed which emerged from another nymph in the same sample.