This one pretty clearly keys to Kogotus, but it also looks fairly different from specimens I caught in the same creek about a month later in the year. With only one species of the genus known in Washington, I'm not sure about the answer to this ID.
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.
Jpsully on Jan 10, 2007January 10th, 2007, 6:59 am EST
Jason:
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 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.'"