Head to head
Cottonmouth vs Eastern Copperhead
The cottonmouth and the copperhead are the two North American members of the genus Agkistrodon, close relatives that share heavy bodies, hourglass-banded young, a yellow-tipped juvenile tail lure, and heat-sensing facial pits. Adults are frequently confused with each other and, more often, with harmless watersnakes. The quickest split is where you find them: the copperhead is a snake of dry woods and rocky hillsides, while the cottonmouth lives in and around water.
| Cottonmouth | Eastern Copperhead | |
|---|---|---|
| Genus | Agkistrodon | Agkistrodon |
| Habitat | In and beside water: swamps, marshes, streams, lake edges | Dry woodland, rocky hillsides, wooded suburbs |
| Adult colour | Dark olive to near-black, pattern often obscured | Pinkish-tan with sharp chestnut hourglass bands |
| Head | Blocky and angular, with a dark stripe through the eye | Smooth coppery, unmarked |
| Threat display | Gapes to show a white "cotton" mouth lining | Freezes silently; relies on camouflage |
| Venom | More potent; strongly tissue-destroying with bleeding effects | The mildest of the US pit vipers |
| Range | The Deep South and lower Midwest, near water | Much of the eastern and central US |
| Danger | A serious bite; still rarely fatal with care | Most US venomous bites, near-zero deaths |
Cottonmouth vs Copperhead: common questions
How can I tell a cottonmouth from a copperhead?
Start with the setting. A pit viper basking on a dry rocky slope or crossing a woodland trail well away from water is almost certainly a copperhead; one swimming in a swamp or coiled on a log over a creek in the Deep South is likely a cottonmouth. Then look at colour and pattern: a copperhead has clean, crisp, chestnut hourglass bands on a pink-tan body and a plain coppery head, while an adult cottonmouth is usually dark and muddy-looking with the pattern faded, a chunkier, more angular head, and a dark mask through the eye. If the snake throws its head back and holds its mouth wide open to show a stark white interior, that is a cottonmouth; copperheads do not do this.
Which one is more dangerous?
The cottonmouth. Its venom is more potent than the copperhead's, its bite delivers more of it, and the tissue damage and bleeding effects can be severe, sometimes leading to lasting injury or amputation without prompt care. It is also more willing to stand its ground and defend itself. The copperhead has the mildest venom of any North American pit viper; it accounts for more venomous snakebites than any other US species, because it is common near people and relies on staying still, but it causes the fewest deaths, and antivenom is often not even needed. Both bites are medical emergencies that require a hospital, and both are very rarely fatal when treated.
Are cottonmouths and copperheads the same snake?
No, but they are close cousins. Both belong to the genus Agkistrodon, the only two North American members, and they can even hybridise where their ranges meet. They diverged from a common ancestor and specialised in different directions, the copperhead into a terrestrial forest ambusher and the cottonmouth into a semi-aquatic generalist that eats fish, frogs, other snakes, and carrion. Their young look very similar, both banded with a bright yellow-green tail tip used as a lure, and it is mainly with age that the cottonmouth darkens and the two become easy to separate.