An artificial fly or fly lure is a type of fishing lure, usually used in the sport of fly fishing (although they may also be used in other forms of angling). In general, artificial flies are an imitation of natural food sources which fly fishers present to their target species of fish while fly fishing. Artificial flies are constructed by fly tying, in which furs, feathers, thread or any of very many other materials are tied onto a fish hook. Artificial flies may be constructed to represent all manner of potential freshwater and saltwater fish prey to include aquatic and terrestrial insects, crustaceans, worms, baitfish, vegetation, flesh, spawn, small reptiles, amphibians, mammals and birds, etc. Effective artificial fly patterns are said to be killing flies because of their ability to put fish in the creel for the fly fisher. There are thousands of artificial fly patterns, many of them with descriptive and often idiosyncratic names.