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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.

Dorsal view of a Ephemerella mucronata (Ephemerellidae) Mayfly Nymph from the Yakima River in Washington
This is an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominal terga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
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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Millcreek has attached these 10 pictures to aid in identification. The message is below.
In alcohol, collected April 3, 2013. Dorsal view, specimen 1.
In alcohol, collected April 3, 2013. Ventral view, specimen 1.
In alcohol, collected April 3, 2013.Dorsal view, specimen 2.
In alcohol, collected April 3, 2013. Ventral view, specimen 2.
In alcohol, collected April 3, 2013. Dorsal view, specimen 3.
In alcohol, collected April 3, 2013. Ventral view, specimen 3.
Live specimen, collected April 18, 2014.
Live specimen, collected April 18, 2014.
Millcreek
Healdsburg, CA

Posts: 344
Millcreek on Jul 17, 2014July 17th, 2014, 3:21 pm EDT
These nymphs are common in the Russian River from mid-February to late April (at least as late instars). I keep going back and forth between D.coloradensis
and D. flavilinea without resolving the issue. I know a lot of folks say to just leave it at D. coloradensis / flavilinea but I thought I'd run it by the folks here and see what you have to say. Size ranges from 9-16 mm (excluding cerci). I put a fairly large number of pictures here to show the range of color variation.
"If we knew what it was we were doing, it would not be called research, would it?"
-Albert Einstein
Entoman
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on Jul 17, 2014July 17th, 2014, 5:15 pm EDT
Boy you sure pick the fun ones, Mark. :) These are photos of flavilinea, at least for now...

The problem for us in CA is that nymphal specimens of these guys meld characters used in the keys from both species. Your excellent photos show prime examples of this. The standard is still Allen & Edmunds '62. They mention this problem with these species in CA and I'm not aware of any later studies that resolve it. Even with this problem in mind, A & E came to the conclusion that they are flavilinea everywhere excepting the Northeastern part of the state where coloradensis holds sway. Based on that I am comfortable with calling yours flavilinea - at least until new research becomes available...;)
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
Millcreek
Healdsburg, CA

Posts: 344
Millcreek on Jul 17, 2014July 17th, 2014, 7:30 pm EDT
Hey Kurt, if I can't carry the load myself I'll hand it to someone else.:)

I used A & E '62 to key the specimens out. I was going with flavilinea myself until I looked at Meyer and McCafferty's Mayflies of California (2008).
While they don't list coloradensis in Sonoma County they do have them listed for Marin and Lake as well as several other counties in NW CA. The problem there is they are based on larval specimens and someone could have confused them with flavilinea. I'm still straddling the fence on this one.
"If we knew what it was we were doing, it would not be called research, would it?"
-Albert Einstein
Entoman
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on Jul 17, 2014July 17th, 2014, 10:11 pm EDT
Yeah, that survey has always been a bit of a puzzle to me. If the key's authors describe them as unworkable for our region, how did workers make determinations in that species survey using them? My hunch is we got us a whole lot o' intergradin' goin' on round heah! :) The grandis sub-species have a similar problem where their ranges overlap.
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
Millcreek
Healdsburg, CA

Posts: 344
Millcreek on Jul 21, 2014July 21st, 2014, 12:37 pm EDT
Took a look at the manual Luke Jacobus and compadres put together for SAFIT and am now inclined to go with Drunella flavilinea because of the broadly triangular spines (at least in relation to Drunella coloradensis).

Unless of course your comment turns out to be correct.
My hunch is we got us a whole lot o' intergradin' goin' on round heah! :)
PC or not, it sure made me laugh.
"If we knew what it was we were doing, it would not be called research, would it?"
-Albert Einstein
Entoman
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on Jul 21, 2014July 21st, 2014, 4:45 pm EDT
Well, Foghorn Leghorn aside, that was the gist of A&E's paper regarding our state. Intergrades between the two species where their ranges overlap coupled with the curious phenomenon of specimens of both becoming more spiny as their ranges move westward toward the coast renders their keys unworkable for us. Sure like to know how the later M&M paper determined that coloradensis inhabits our coastal counties.
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
Millcreek
Healdsburg, CA

Posts: 344
Millcreek on Jul 21, 2014July 21st, 2014, 5:29 pm EDT
I suspect that another quote, one from Cool Hand Luke might sum it up. The warden of the chain gang when he addresses the convicts, "What we have here is a failure to communicate."
"If we knew what it was we were doing, it would not be called research, would it?"
-Albert Einstein
Entoman
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on Jul 21, 2014July 21st, 2014, 6:27 pm EDT
:)

"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
PaulRoberts
PaulRoberts's profile picture
Colorado

Posts: 1776
PaulRoberts on Jul 22, 2014July 22nd, 2014, 1:00 am EDT
Nice discussion guys. Thanks.
Crepuscular
Crepuscular's profile picture
Boiling Springs, PA

Posts: 920
Crepuscular on Jul 22, 2014July 22nd, 2014, 5:25 am EDT
Well, Foghorn Leghorn aside, that was the gist of A&E's paper regarding our state. Intergrades between the two species where their ranges overlap coupled with the curious phenomenon of specimens of both becoming more spiny as their ranges move westward toward the coast renders their keys unworkable for us. Sure like to know how the later M&M paper determined that coloradensis inhabits our coastal counties.


What? Variation among the Ephemerellids, no way...

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