Procambarus clarkii is a freshwater crayfish species, native to the Southeastern United States, but found also on other continents, where it is often an invasive pest. It is known variously as the red swamp crawfish, red swamp crayfish, Louisiana crawfish, Louisiana crayfish or mudbug
The native range of P. clarkii is along the Gulf Coast from northern Mexico to the Florida panhandle, as well as inland, to southern Illinois and Ohio. It has also been introduced, sometimes deliberately, outside its natural range to countries in Asia, Africa, Europe and elsewhere in the Americas. In northern Europe, the populations are self maintaining but not expanding, while in southern Europe, P. clarkiiis multiplying and actively colonising new territory, at the expense of the native crayfish, Astacus astacus and Austropotamobius spp. Individuals are reported to be able to cross many miles of relatively dry ground, especially in wet seasons, although the aquarium trade and anglers may have hastened the spread in some areas (it is believed that anglers using P. clarkii as bait introduced it to the American state of Washington). Attempts have also been made to use P. clarkii as a biological control organism, to reduce levels of the snails involved in the life cycle of schistosomiasis, leading to the dispersal of P. clarkii in, for instance, Kenya.