The Isonychias or Slake Drakes are an important mayfly hatch particularly here in the East. Fly tier, blogger and author Matt Grobert, whose book "Fly Fishing New Jersey Trout Streams" recently went into it's second printing, is going to tie this Iso Emerger. It's a pattern that's both easy to tie and remarkably effective.
Matt begins by mashing the barb on a Dai-Riki #125 size 12 emerger hook and securing it in his vise. As is so often the case, he's going to use 6/0 olive Danville for his tying thread. Start the thread on the hook shank leaving some space behind the eye. Take wraps down the shank to just beyond the barb and break or snip off the tag.
For the trailing shuck, Matt snips a small segment of dark brown Zelon and wets it a little bit to keep the fibers together. Lay the fibers against the near side of the hook and allow thread torque to carry them to the top. Fibers should extent forward to the start of your thread wraps. Take wraps down the bend of the hook a ways and then snip the Zelon off to form a trailing shuck about a half a hook shank in length.
For dubbing, Matt uses his own custom Isonychia blend but commercially available blends work just fine. Start with a fairly significant pinch of dubbing and begin applying it to your tying thread, a little bit at a time. Keep the noodle thin but you're going to need to make it rather long, enough to cover about 3/4's of the hook shank. Take wraps so the dubbing noodle starts right at the base of the tail and continue wrapping forward to create the body of the fly. The body should end at about the point where your thread wraps started.
For the emerging wing, Matt uses dun colored comparadun deer hair. Snip a small clump, then remove the fluff and short fibers from the butts and place the clump in a stacker. After a few good taps, carefully get hold of the aligned tips and remove the clump from the stacker. Place the hair on top of the hook so the tips extend just beyond the bend. Take a couple of loose wraps of tying thread and then pull straight up and take a few more wraps to secure the hair to the hook.
Pull the butt ends up and back and take wraps to form a small thread dam in front of the hair. While pulling the butt ends back and out of the way, finish the head of the fly with a 5 or 6 turn whip finish and then snip or cut your tying thread free. Pull the butt ends to vertical and snip them off at an angle, like so. You'll most likely miss a few of the butt hairs but these can be easily trimmed out.
And there you have it, a finished Isonychia Emerger. Hang on tight when you're fishing these as trout have a tendency to really hit them hard.