Cottonmouth vs Brown Water Snake

The quick tellBrown water snakes have rows of square dark blotches, round pupils and no heat pit. Cottonmouths are darker and have a dark stripe through the eye.

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: unknown author, CC BY 3.0, via Wikimedia Commons

Brown water snake

Harmless · Nerodia taxispilota

Brown with square dark blotches in rows along the back and sides
Head wider than neck, which makes people think viper
Round pupils, no heat pit
Often basks on branches over water

Size: 30–60 in. Habitat: Rivers, lakes and cypress swamps of the Southeast.

Not venomous.

Where each one lives

Cottonmouth only
Brown water snake only
Both
Neither

Cottonmouth: 15 states. Brown water snake: 7 states. Both live in 7 states.

Side by side

	Cottonmouth	Brown water snake
Danger	Dangerous	Harmless
Size	30–48 in	30–60 in
States	15	7
Habitat	Swamps, slow rivers, marshes and ditches of the Southeast	Rivers, lakes and cypress swamps of the Southeast

Questions

How can you tell a cottonmouth from a brown water snake?

Brown water snakes have rows of square dark blotches, round pupils and no heat pit. Cottonmouths are darker and have a dark stripe through the eye.

Which one is dangerous?

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

Where do both live?

Both live in 7 states: Alabama, Florida, Georgia, Louisiana, North Carolina, South Carolina and Virginia.