‹ Compare two snakes
Northern Cottonmouth vs Diamond-backed Watersnake
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Melanie Gaddy, no rights reserved
Northern Cottonmouth
Agkistrodon piscivorus
Venomous(c) Kara Matthews, some rights reserved (CC BY)
Diamond-backed Watersnake
Nerodia rhombifer
Non-venomousThe quick way to tell
Check the face. The cottonmouth has a vertical pupil and a dark eye mask. The Diamond-backed Watersnake has round pupils and a net-like pattern.
Eyes ★ This settles it
Vertical slit pupil; heat-sensing pit between eye and nostril.
Round pupil, eyes set high on the head; no heat-sensing pit.
Head
Blocky, heavy brow, dark mask through each eye, pale snout.
Narrow head with a pale, heavily marked jaw.
Pattern
Dark olive to nearly black, with faint wide bands clearest on young snakes.
Dark chain-link or diamond-mesh pattern on olive to yellow-brown, with dark side bars.
Pits
A deep heat-sensing pit on each side of the face, between the eye and the nostril.
None. There is no pit between the eye and the nostril.
Tail
Thick-based; young have a yellow tail tip.
Thick-based, tapering; no rattle.
What it does
Coils, vibrates its tail and gapes to show a white mouth lining.
Hangs in brush above water and drops in when approached.
Where it lives
Southeast from southeastern Virginia through the Carolinas, northern Georgia and Alabama, west to central Texas and Oklahoma, and up the Mississippi valley to southern Illinois, Missouri and southeastern Kansas.
Central US: Mississippi valley from Illinois and Indiana south to the Gulf, west across Texas, Oklahoma and Kansas.