Agkistrodon piscivorus
The Cottonmouth, or water moccasin (Agkistrodon piscivorous), is a venomous snake closely related the to the copperhead. Unlike most snakes, including the copperhead, when startled the cottonmouth will stand its ground and open its mouth ("gape" or "smile"). The cottonmouth's range is only in the southern United States, with the northernmost population occuring in southern Illinois.
Many harmless snakes are killed from the mistaken belief that they are cottonmouths. The cottonmouth range is in the following states: