Mayfly ID

creekx

Director of Stoke
Encountered this mayfly hatch on a North Idaho stream. Sorry for the crap phone photo. I was on the oars and could not access my DSLR.

Some type of Heptageniidae clinger like Epeorus or Heptagenia? About a size 15, plain wings, large hind wings, two tails. It may have the dark, heart-shaped spot on the forelegs like Epeorus. Are the light, contrasting edges of the body segments a tell?

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Mark Melton

Active Member
I'm really not sure, with it being a subimago and not being able to tell the sex due to the picture being out of focus, but I'd guess Rhithrogena. Here's pictures of a female and male imago to compare.


 

creekx

Director of Stoke
I'm really not sure, with it being a subimago and not being able to tell the sex due to the picture being out of focus, but I'd guess Rhithrogena. Here's pictures of a female and male imago to compare.


It is a male - tough to see but has large eyes and clasper. Doesn't help that its the same color as my hat!

Don't rhithro wings typically have pronounced veining or a leaded-glass window appearance?

Correction about the heart-shaped spot on the forelegs like Epeorus - meant to say femur. It's barely distinguishable.

It looks a lot like this Epeorus pleuralis which is an Eastern species though:

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Mark Melton

Active Member
Rhithrogena wings may or may not have pronounced veining or a leaded-glass appearance. I've seen a fair number that are relatively clear with a minimal veining. All depends on the species I guess.
There don't seem to be many species of western Epeorus that have been photographed with the exception of the two most common ones, E. longimanus and E. albertae and those two are lighter in appearance than your mayfly. However there are several western species that haven't been photographed (at least not that I know of) and the descriptions depend heavily on the penes.
 

jamma

Active Member
Hard to tell without a detailed close-up, which is usually the case, but I think Heptagenia fits better here. Check your sources and see if you don't agree.
 

Mark Melton

Active Member
It's possible. Near as I can tell Idaho has three species of Heptagenia, H. elegantula, H.solitaria, and H. adaequata. I did find pictures of all three at Troutnut and Bugguide. However, none of them are of subimagos. Here are links to the photos. Don't think we'll be able to come to any conclusion without either a detailed photo of the penes or a specimen in hand.



 

Troutnut

Active Member
I photographed a female Rhithrogena hageni dun from the Cascades on July 4th. There's no key to species for female duns, but I caught a similar-looking male spinner on the same trip so I'm assuming they're the same species. The body proportions and markings on the tergites (top of the abdomen) look pretty similar to yours. The color looks similar, too, given that mine was under brighter lighting.



I would be pretty confident calling your mayfly Rhithrogena, maybe hageni, but a different species can't be ruled out.
 

creekx

Director of Stoke
Another one from N Idaho. Very large, about a size 10. I asked an acquaintance of mine, who has authored several books on hatches, for an ID. He said it is definitely a Heptageniid but would like to see a spinner for ID purposes.

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Troutnut

Active Member
I agree with your friend that it's a Heptageniid (they just have a "look" to them with the way he legs and head are sort of compressed) and it's hard to go farther from this picture. If you have any other photos, specifically one in which the tips of the wings are in focus, we might be able to tell if it's Rhithrogena or something else.
 

Joel K

New Member
Encountered this mayfly hatch on a North Idaho stream. Sorry for the crap phone photo. I was on the oars and could not access my DSLR.

Some type of Heptageniidae clinger like Epeorus or Heptagenia? About a size 15, plain wings, large hind wings, two tails. It may have the dark, heart-shaped spot on the forelegs like Epeorus. Are the light, contrasting edges of the body segments a tell?

View attachment 243093
Another one from N Idaho. Very large, about a size 10. I asked an acquaintance of mine, who has authored several books on hatches, for an ID. He said it is definitely a Heptageniid but would like to see a spinner for ID purposes.

View attachment 246932

I would say that this is a March Brown Mayfly, "Maccaffertium Vicarium"Common on most lakes in the PNW usually in Spring and early Summer.

Good fishing!
Joel
 

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