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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.

Ventral view of a Hydropsyche (Hydropsychidae) (Spotted Sedge) Caddisfly Larva from the Yakima River in Washington
With a bit of help from the microscope, this specimen keys clearly and unsurprisingly to Hydropsyche.
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.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Lateral view of a Male Ephemerella subvaria (Ephemerellidae) (Hendrickson) Mayfly Dun from the Beaverkill River in New York
I collected this male Hendrickson dun and a female in the pool on the Beaverkill where the popular Hendrickson pattern was first created. He is descended from mayfly royalty.
bedminster, nj

Posts: 4
Jpsully on Jan 10, 2007January 10th, 2007, 6:59 am EST

Looking at the fifth photo from the top (the one with the ruler under the fly), it would appear that if you were to rotate the fly just a bit to the left, it would show that the fly is over one inch (25mm) long. That would make it twice as long as any Hendrickson I have ever seen. The average Hendrickson (to the best of my knowledge) is usually around 10-12mm (or about 1/2 inch), hook size 10-12. The hook size just doesn't seem to fit either. Where am I going wrong when looking at this fly (and hook)?

Martinlf's profile picture
Palmyra PA

Posts: 3047
Martinlf on Jan 10, 2007January 10th, 2007, 7:42 am EST
JP, Unless I'm mistaken, I believe that the ruler Jason is using is metric, that each little increment is one mm. I then see the bug measured at about 9-10 mm in the photo (not counting, of course the tails), and size 12 fits your accurate observations about the typical Hendrickson hook size. Now, when and where will we start seeing this bug come spring? I'm ready now.
"He spread them a yard and a half. 'And every one that got away is this big.'"

--Fred Chappell
Troutnut's profile picture
Bellevue, WA

Posts: 2758
Troutnut on Jan 10, 2007January 10th, 2007, 7:54 am EST
Louis is right: it's a metric ruler, and the fly's body is about 11mm long.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist

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