This is a simple version of how a row of fly stitch can be decorated using a contrasting colored thread.

To do this stitch, you need to know how to do the fly stitch.

whipped_fly_stitch_1      whipped_fly_stitch_2
Fig 1: First make a vertical row of fly stitch. To whip, take a contrasting  thread and start from the tip of the first tail. Whip the thread around each tail as shown in the illustration. Be careful not to pluck the fabric beneath.   Fig 2: A finished row of whipped fly stitch would appear like this.