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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.

Artistic view of a Perlodidae (Springflies and Yellow Stones) Stonefly Nymph from the Yakima River in Washington
This one seems to lead to Couplet 35 of the Key to Genera of Perlodidae Nymphs and the genus Isoperla, but I'm skeptical that's correct based on the general look. I need to get it under the microscope to review several choices in the key, and it'll probably end up a different Perlodidae.
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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Gutcutter has attached these 5 pictures to aid in identification. The message is below.
PaulRoberts
PaulRoberts's profile picture
Colorado

Posts: 1776
PaulRoberts on May 7, 2012May 7th, 2012, 7:04 am EDT
I've known pleuralis to be olive and vitreus to be yellower with an orange (sometimes quite bright) abdomen. I assume this is in females only but I don't remember.

As far as being certain, I guess they'd have to be keyed out.
Entoman
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on May 7, 2012May 7th, 2012, 9:11 am EDT
They are 9.5 mm. I pickled them and when I get some time, which will not be today I'll try and run them through the keys..

As far as being certain, I guess they'd have to be keyed out.

I'm not aware of any reliable keys for determining between the two species without male imagos. If you had them, size wouldn't help but vitreus has more prominent penes easily distinguishable from pleuralis and usually dark medial marks on the terga lacking on pleuralis. I'm pretty sure male duns aren't developed enough to show either trait with any clarity unless it's a really good closeup photo.

All we really have are the old angler's guidelines regarding duns:

1. Earlier, darker, tan & gray tinted - pleuralis

2. Later, lighter, yellow & orange tinted - vitreus

Frankly, I didn't notice the amberish hues on Tony's specimen and based my initial opinion on timing. The lighting is such in his photos that it looked dark enough to not raise an alarm about its shade either. I wasn't sure about Eric's which is why I left my comments about his photos at the genus level. After comparing the two more closely and taking into account the different lighting, its pretty obvious that Tony's and Eric's are the same species.

Good job, Paul. I have to agree with you that they are probably vitreus. So much for counting on timing this year, huh? :)
"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
Entoman
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on May 9, 2012May 9th, 2012, 12:18 pm EDT
Guys -

I'm embarrassed to admit another character completely overlooked - the pale tails! E. pleuralis has pretty dark ones. OOPs...
"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

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