The technique of fly fishing nymphs for trout originated in England and then spread worldwide through the writings of G. E. M. Skues and other advocates of upstream nymph fishing. Arguably one of the most notable advocates was Frank Sawyer, a River Keeper on the English chalk stream Avon, who is credited with inventing the Pheasant Tail nymph in order to imitate small baetis insects. Nymph fishing flies imitate the early stages of an insect's life, and these artificial flies are designed to represent larvae that are either dislodged from the bottom of a rock or moving upward to shed their outer skin and reveal wings. The "sink and draw" method for how to fish nymphs by imitating this larval movement was developed on Sawyer's River Avon. Anglers would allow the nymph fly to sink before pulling in the line or raising the rod tip to make it swim upwards to the water surface. This movement was intended to replicate the natural motion of an emerging insect making its way from the riverbed to the surface. The ultimate aim was to have the fly positioned in front of a specific fish and entice it to bite. The English approach has been modified and improved to suit local fishing conditions, especially in the United States. Overall, nymphs are an effective and popular choice for fly fishing enthusiasts, and slim, streamlined patterns are in demand. Like the Pheasant Tail, the Gold Ribbed Hair's Ear nymph, the Prince Nymph, and their bead head variants are staples in the fly fishing world. Other nymph flies fish can't ignore (and, therefore, neither should fly fishers) include another classic pattern, the Copper John, dry-dropper favorite Zebra Midge, and the stoneflies, which fly tiers have been making prior to the year 1500.