Author and fly tier Matt Grobert came up with this fly in an effort to construct a more durable Griffith's Gnat. He calls it "Matt's Gnat". The pattern first appeared in the March 1996 issue of Fly Fisherman magazine. It's kind of amazing how far fly tying instruction has come since then.
Here Matt's going to tie his namesake gnat on a TMC 2488 in size 20. He begins by mashing the barb and securing the hook in his vise. For thread, Danville 6/0 in either burgundy or claret is a good choice.
Start your thread on the hook shank leaving some space behind the eye and wrap rearward to halfway between the point and the barb.
Select a single peacock herl from either a quill or a strung bundle. Lay the herl against the near side of the hook and begin taking wraps to secure it to the shank. Thread torque should make the herl lay on top of the hook. Apply a light coating of tacky wax to about an inch and a half of your tying thread.
Snip a small clump of hair from a natural colored snowshoe rabbit's foot. Gently pull the longer guard hairs free from the clump and dispose of them. You should be left with a smaller clump of nicely colored shorter hairs. Then, snip the fuzzy underfur away. Taking only small amounts at a time, touch dub the hair to the tacky wax on your tying thread.
Once you have the hairs evenly distributed, double your tying thread over and take wraps to secure the dubbing loop to the hook shank. Then wrap your thread forward to just behind the eye.
Carefully insert the peacock herl into the dubbing loop and pull everything towards you into an even length. Using both hands, spin the loop and the herl to form a dubbing rope. With that done, begin taking wraps around the hook shank with the rope. With every wrap, stroke the fibers rearward to keep the majority of them pointed back. When you reach the eye, take a couple of good firm wraps of tying thread over the top of the rope to secure it. Then take some wraps in front of it to lock everything in place. Snip the remainder of the rope off. Often, there'll be enough to make a second fly.
Finally, whip finish and cut your tying thread free. Fish a Matt's Gnat anytime you'd normally fish a Griffith's. You'll find it floats great, and holds up really well.