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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.

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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Lateral view of a Male Stenonema modestum (Heptageniidae) (Cream Cahill) Mayfly Dun from the Teal River in Wisconsin
Site Editor
"Bear Swamp," PA

Posts: 1681
GONZO on Nov 26, 2006November 26th, 2006, 6:02 am EST
Hi Jason-

While scanning the Stenacron specimens in response to Jeff's question, I came across this one. It does not appear to be Stenacron. It lacks the dark pigmentation (spot) between R1 and R2 that is distinctive of this genus. Clearly, it is a member of the Heptageniidae, but I haven't found a definitive clue to indicate which one it might be. Perhaps someone else will detect something more conclusive.
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on Feb 6, 2012February 6th, 2012, 12:20 pm EST
Somehow this one fell through the cracks. I agree with Gonzo this isn't Stenacron, and for the same reasons. It's also not Stenonema due to the lack of median posterior dark spots on the terga. The excellent ventral detail of the photo showing ridges on the prosturnum and the orientation of the furcasturnum clearly show it to be a member of the subfamily Heptageniinae. Due to eye separation and tarsi segment comparisons (among other characters) Maccaffertium male subimago from one of the spread eyed species is the likely choice.

This looks like Maccaffertium modestum, one of the Summer Cahills. Size isn't mentioned, but based on its proportions this specimen looks to be on the small side of the range scale for this species and fits well with the descriptions of the Midwestern rubrum form. Other species possibilities in this genus with which it could be confused are much larger. Tergal markings (spiracular dots, full length posterior dark lines), lack of crossvein crowding below the bullae, and the dark tail articulations are further positive characters. Together with matching color descriptions, relative abundance, and reported distribution in the specimen's locale, I think modestum is a reasonable opinion. ... The good news is this adds a more complete picture to the hatch page that was lacking a dun until now.
"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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