The Fly Stitch is seldom used in smocking, as it is a bit difficult to work the needle at the right place on the pleat.

Start with the thread coming to the front of the fabric on the tip of the pleat. Insert the needle at an angle through the pleats, catching the thread under the needle (Step 1). Be sure to take only a very small "bite" out of the tops of the pleats, because this is an embellishment stitch. Pull the thread so that it forms a "V", and anchor with a tiny stitch at the tip of the "V" (Step 2).

Alternatively, you can anchor the "V" with a longer stitch if you want to, so that the finished stitch looks like a "Y".