Cottonmouth vs Water Snake

The quick tellA cottonmouth floats with its whole body riding high on the surface. A water snake swims with only its head up, and up close it has round pupils and no heat pit.

Photo: kirk gardner, CC BY 4.0, via iNaturalist

Cottonmouth

Dangerous · Agkistrodon piscivorus

Heavy, dark olive to black body; bands fade with age
Broad flat head with a dark stripe through the eye
Swims with the whole body high on the water
Opens its mouth wide to show the white lining when threatened

Size: 30–48 in. Habitat: Swamps, slow rivers, marshes and ditches of the Southeast.

A bite is a medical emergency. Most snakes people call water moccasins outside its range are harmless water snakes.

Photo (Plain-bellied water snake, one of several US water snakes): Patrick Coin, CC BY-SA 2.5, via Wikimedia Commons

Water snake

Harmless · Nerodia spp.

Round pupils
No heat pit between eye and nostril
Head often not much wider than the neck when relaxed
Swims with only the head above water

Size: 24–48 in. Habitat: Almost any lake, pond, creek or ditch in the eastern half of the country.

Not venomous. Water snakes bite hard if grabbed and flatten their heads when scared, which is why they get killed as moccasins.

Where each one lives

Cottonmouth only
Water snake only
Both
Neither

Cottonmouth: 15 states. Water snake: 38 states. Both live in 15 states.

Side by side

	Cottonmouth	Water snake
Danger	Dangerous	Harmless
Size	30–48 in	24–48 in
States	15	38
Habitat	Swamps, slow rivers, marshes and ditches of the Southeast	Almost any lake, pond, creek or ditch in the eastern half of the country

Questions

How can you tell a cottonmouth from a water snake?

A cottonmouth floats with its whole body riding high on the surface. A water snake swims with only its head up, and up close it has round pupils and no heat pit.

Which one is dangerous?

The cottonmouth: dangerous. The water snake: harmless. If you are not sure, keep your distance and do not handle it.

Where do both live?

Both live in 15 states: Alabama, Arkansas, Florida, Georgia, Illinois, Kentucky, Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee, Texas and Virginia.