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3. Nixe?

Folks, I posted this pick a while back and think I called these Rhithrogena then. But I'm thinking it's Nixe. I noticed the upper nymph has split, and beneath is a creamy colored dun about to pop. They were small (you can see some Neothremma next to them) -about a #16 hook.

Two Nixe species, criddlei and simplicioides, are listed in Ward and Kondratieff (1992) in this watershed. The pale last tergites are notable on these guys.

There isn't sufficient resolution to pick out terminal filament setae to separate Nixe from Heptagenia (and Leucrocruta is not listed in this watershed at that time), so I guess I'm looking for your gestalt impression.

I think we might be looking at something else here, Paul. I'm fishing this weekend, but when I get back home I'll go through my stuff. Like you, I wish the photo offered a better look at the caudal filaments - gills and head capsules too. The small heads bother me a little, but that could be the result of the thorax swelling as these critters look ready to pop any moment.

BTW - I think you meant Ecdyonurus, not Nixe. The species you mentioned are in the former genus.

I zoomed in on the image and found that the gills are large and clear (not veined), and the caudal filaments do have setae at the joints. There are 3 tail filaments btw -some are broken in the image. I had a Cynigmula that day and it was different (jaw process, and veined gills), although it too had the pale last tergites.

Looking at the large clear gills now, and I'd be surprised that I wouldn't have flipped them over to view them, I'm starting tho think Rhithro again. But, are there any pale cream colored dun Rhithro's?

Ecdyonurus changed to Nixe. OK. That's why I gave the source and date of the text I used.

Check out my edit above.

Yeah, the constant name revisions are a pain. Good thing you mentioned species or we would have been talking about different genera without realizing.:)

Interesting that you mention Cinygmula as I was leaning in that direction. I wouldn't rule them out just yet. Their "horns" can be obscured during the eclosion process due to head capsule deformation. I seem to remember a conversation with Luke and Jason where this came up.


Not that I'm aware of.

I remember that conversation. Possibly Cynigmula. Why not Ecdyonurus?

Here's the Cynigmula I found that same day. It's less mature, was smaller, and has prominently veined gills. A different critter I believe(d):



Here are the heads of the two mayflies:


The closer I look, the more similar they are -minus maturity, pigment, and mouth process (whatever its called). The bugs in question might just be a Cynigmula.

Ah, there we are...

I think the critters in the first photo are the same as this guy. All are Cinygmula, probably C. tarda or ramaleyi (Western Ginger Quill). Of the four species reported from CO they seem the most likely as the other two are much larger. The odds of two different genera in the same location having the same pale segs 8,9, & 10 coupled with the rectangular pale area on the head's anterior is beyond remote. This marking pattern is a common cinygmula character.


Besides the horns showing in the last photo, from what I know of Ecdyonurus they usually have fairly spotted terga and variegated patterns on their thoraxes. The overall solid amber-brown coloration and ringed abdomens are traits usually found in the Rhithrogeninae subfamily not the Ecdyonurinae. Another character difference is the more tear drop shaped conformation of Ecdyonurus, usually with a much wider head capsule in relation to body length. The slender femurs on these specimens is another clue.

Oops! I was posting while you edited yours. Yeah, it clearly shows the distortion the head capsule is undergoing. The duns head is probably mostly out of it. If you look closely you can make out the pale area that now has nothing up against it.

BTW - The one uppermost in the first photo is male. See the duns large eyes showing through? The larger bottom nymph is female.

Check out Jason's photos taken last Summer. The detail is amazing! tarda is reported in AK. They are more smokey brown, but I'm sure that is adaption to the substrate.
http://www.troutnut.com/specimen/981

Excellent analysis.

I see mimus and par listed by W&K 1992 as having been collected in my watershed. Love to know more about them.

Thanks for the help, Kurt. Hey, shouldn't you be fishing?

Found this:

Jensen,SL 1966 The Mayflies of Idaho (Ephemeroptera). M.S. Thesis, University of Utah, Utah. 364 p.
Quote from pages 154 and 155: "The mimus group, ...
Nymphs of this species are found in small to moderate streams usually above elevations of 5,000 feet, on rocks and among gravel. Adults swarm in the early evening and on cloudy days, usually from 3-5 feet over riffles in the stream. They have been colected from May to August."

Also a 1924 mimus dun description saying the wings are brownish-yellow at the bases. Coupled with the relatively slow water they like, a rabbit foot pattern using snowshoe hare for the wing will be ideal. Also, a cream-colored wet fly pattern with aftershaft wing (already have those). Will have to catch some spinners to see what they are like.

Ha! The fishing on Pyramid for those monster cutts is an early proposition. Wind comes up bad about lunch time. Now I'm sitting around with nothing better to do than play with bugs on my I-phone!:)

BTW - not so fast with the compliments. I got a little dyslexic with the species and got them reversed. My bad, sorry about that. I've edited the above to correct the error. C. mimus is the big species.

Do you remember any of these flying about when you collected those ripe nymphs?
http://www.troutnut.com/specimen/976

Ugh! Who's tarda? I don't see it listed. Guess I'll have to check the MFC list.

ramaleyi is described, (and seen in Jason's images), as rusty dun, rather than cream. Might they darken that much?

Well, it's a little species, and the only one of the four documented in CO that doesn't grow beyond 8.5mm, the rest can get at least as large as 11 mm. C. mimus is a big boy of the genus documented between 10 & 12mm. What is interesting is that it is also found in AK (ramaleyi isn't). That's why I posted that link to Jason's nymph the similarity is pretty striking. The problem is it's supposedly very rare while ramaleyi is pretty common and can be that small... So, we have to pick our poison.:)

Yes, C. par is also an option. Though they can get as big as 11 mm, they have been documented as small as 8mm. The fact that you have documentation of only this species and the larger mimus in your watershed is pretty strong evidence for it! C. par is also in AK, so the similarity of your's and Jason's photos remains intriguing.


Sure. That one photo I linked looked pretty pale. When it was first hatching I bet it looked pretty bright.

Thanks Kurt.

Baby steps. :)

You're welcome. One thing that I forgot to mention is how beautiful they can be. I remember an occasion backpacking with my young sons when we came across a small high country stream crossing. There was a pretty good hatch of these guys coming off and the light was just right to silhouette their wings against the cobalt blue of the water. We were looking into a very dark gray sky with the sun at our backs. You know how that kind of condition makes color so vibrant? One of the most beautiful sights I've ever seen ... Check out the link and place this guy on the water to catch my drift.

http://www.troutnut.com/specimen/798

Very nice description, Kurt. We sure are blessed to do what we do. I can literally tear up at certain times and places. I say, "LOOK where I am!!"