The cottonmouth, also known as the water moccasin, may be the most feared animal in the eastern United States. People panic about cottonmouths in areas where cottonmouths don’t even live. Growing up in West Virginia, which is decidedly outside the cottonmouth’s range, I was told by several people that they had killed or been chased by “moccasins” in the creeks. This was highly unlikely.
Some of the fear is justified: cottonmouths are venomous, and they’re more common than the larger diamondback and timber rattlesnakes, with more venom than the smaller pigmy rattlesnakes and copperheads. Either way you’re ranking threat level — number of bites or seriousness of bites — the cottonmouth falls somewhere in the middle.
So, why do they have such a bad reputation? One possibility is mistaken identity. The Nerodia genus of non-venomous water snakes can be found pretty much anywhere with fresh water, and they are often misidentified as cottonmouths. They’re both fairly large, heavy-bodied, dark-colored snakes usually found near water; it’s an understandable mistake. After all, who wants to get up close and check the shape of the pupil or the color of the inside of the mouth?
This explains the “cottonmouths” encountered in the Appalachians and northeastern states. It also might be responsible for much of the cottonmouth’s reputation for aggressive behavior. Water snakes are defensive when cornered, and they can look pretty intimidating. Unfortunately, this often backfires and gets them killed by people who think they’re venomous.
But if you’ve seen a cottonmouth that feels threatened, you’re unlikely to confuse the two again. Cottonmouths get their name from their very distinctive defensive posture, in which they flatten their bodies to look even bigger, raise their heads, and open their mouths wide to display the white inside and the fangs. This is a warning, and it is a good idea to heed it.
The actual range of cottonmouths is much smaller than that of the various water snake species combined. They live in swamps, rivers, and lakes in the Southeast coastal plain, the Gulf states, and a bit of the Midwest, including parts of Oklahoma, Missouri, and Indiana. If you see one, the best thing to do is walk around, giving it a few yards of space.