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.
This is the only Heptageniid mayfly I saw hatch on May 24, 2004, and luckily it floated right by me.
Edit: Gonzo confirmed most likely vicarium 06.21.12
This mayfly was collected from the Namekagon River in Wisconsin on May 24th, 2004 and added to Troutnut.com by Troutnut on January 25th, 2006.