They are tied with plastic yarn although I tie them with sparkle yarn, angora yarn or glo bug yarn also. It's an easy tie but effective pattern....good one to fill the box up with. I can lose them as fast as I tie them.
Lay a heavy thread base down of a color usually brighter than the yarn. Split the yarn into its individual plies. I like to combine different colors. Tie them in at the back of the hook shank. Form loops with the yarn and keep tieing them down working to the eye of the hook. Tie off and trim the tags from the front and back.