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Water moccasins (Agkistrodoon piscivorus) are the only poisonous water snake native to the southern United States. They’re commonly found in swamps, streams, marshes, and drainage ditches rather than in fast-moving or deep water. Water moccasins usually avoid human contact, but if startled, unlike other snakes, the water moccasin occasionally stands its ground rather than fleeing. When they do this, they open their mouths as wide as possible, showing the white insides and thus giving them the name “cottonmouth.”

Adult water moccasins are 30 to 48 inches long. The young are born live and have darker, more contrasting crossbands and a yellowish tail tip. As they grow older, their colors become a uniform olive gray, grayish brown, or black with a lighter belly. Water moccasins have elongated, black heads with blunted noses. Because several other water snakes resemble the water moccasin, more of these non-poisonous snakes are killed each year than are moccasins.