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.
I've seen Ephemerella invaria with green egg sacs and Ephemerella subvaria with yellow one. This one seems too large for dorothea. So what is it? I'm not sure.
Many females of this species were gathered in tight clouds to lay their eggs over the riffles in a mid-sized Pocono stream right at dusk. It would have been a fishable spinner fall if I'd stuck around to wait for them.