Northern Cottonmouths Agkistrodon piscivorus are one of two recognized species of large (76-114 cm record 188 cm) semi-aquatic pitvipers in eastern North America. Florida has a closely related but distinct species, the Florida cottonmouth Agkistrodon conanti.

Cottonmouths are venomous, and are therefore dangerous if approached closely or handled. They are not generally aggressive and will most likely flee any confrontation if given a chance to retreat. Some may bluff charge or boldly move towards humans to get out of a cornered situation, but have never been recorded chasing people.

Northern Cottonmouths are dark, possibly faintly patterned snakes (except as juveniles), best known for their defensive posture with a gaping, white lined mouth. They are also distinguishable from most watersnakes by their sharp brow ridges and dark stripe over the eyes.

The specific epithet "piscivorus" describes the one of the prey species of the cottonmouth - fish. The cottonmouth is also fond of frogs, mammals and other snakes. Although it may be commonly seen in lakes and ponds frequented by humans, few fatalities are recorded as a result of bites by cottonmouths.

Comparison of juvenile vs adult cottonmouth.

Species Complex Map | Relevant/Recent Phylogeography

The Agkistrodon piscivorus species complex has been delimited using modern molecular methods and two species with no subspecies are recognized. There is a zone of admixture between the two cottonmouth species where they overlap around panhandle Florida.

This short account was prepared by /u/unknown_name and edited by /u/Phylogenizer.

Snakes with medically significant venom are typically referred to as venomous, but some species are also poisonous. Old media will use poisonous or 'snake venom poisoning' but that has fallen out of favor. Venomous snakes are important native wildlife, and are not looking to harm people, so can be enjoyed from a distance. If found around the home or other places where they are to be discouraged, a squirt from the hose or a gentle sweep of a broom are usually enough to make a snake move along. Do not attempt to interact closely with or otherwise kill venomous snakes without proper safety gear and training, as bites occur mostly during these scenarios. Wildlife relocation services are often free or inexpensive.

If you are bitten by a venomous snake, contact emergency services or otherwise arrange transport to the nearest hospital that can accommodate snakebite. Remove constricting clothes and jewelry and remain calm. A bite from a medically significant snake is a medical emergency, but not in the ways portrayed in popular media. Do not make any incisions or otherwise cut tissue. Extractor and other novelty snakebite kits are not effective and can cause damage worse than remaining calm, seeking help and waiting for professional evaluation.

There are a few things that can help differentiate between cottonmouths (A. piscivorus, A. conanti) and harmless water snakes (Nerodia spp.) once you learn to recognize them properly. It's important to try to apply as many keys as possible; the more of these characteristics you can accurately identify, the more reliable your ID will be. Underlined text links to pictures to help illustrate the keys.

1. Cottonmouths have a prominent, angular ridge along the top of the head, starting around the supraocular scale (directly above the eye) and running forward toward the snout (side view, front view). This ridge protrudes outward, partially overhanging the eye like a brow, and gives the snake an annoyed or grumpy looking appearance. This also partially obscures the eyes when viewed from above. In water snakes, the supraocular scale does not overhang the eye, giving the animal a 'derpy' appearance from the side or head on, and allows you to see most of the eye from above.

2. Cottonmouths have white or cream colored horizontal stripes or lines that run from below the eye toward the corner of the mouth, and often another that runs from behind the top of the eye toward the point of the jaw. Water snakes do not.

3. Water snakes usually have dark, vertical bars along the edges of their labial scales. Cottonmouths do not.

4. Cottonmouths and water snakes both darken with age, and the pattern is often obscured by the time they reach adulthood. When the dorsolateral pattern IS visible, cottonmouths have bands that are usually wider at the bottom than on top; like pyramids in side view, or hourglasses from above. In some individuals, the bands might be broken or incomplete, so this is not 100% diagnostic, but is still useful when used in conjunction with the other keys. Water snakes exhibit a wide variety of patterns; most species aren't banded at all, and the ones that are banded have bands that are wider at the top, like upside down triangles.

5. Adult cottonmouths often have a noticeable dorsal ridge along the vertebrae. This gives the body a triangular appearance in cross-section, which is especially noticeable in underweight or dehydrated animals, or when they initiate a defensive display. Water snakes, by contrast, are more cylindrical in cross-section.

6. Baby cottonmouths are born with yellow or greenish tail tips (used to lure small prey) that fade as they age. Young water snakes do not have these (baby N. sipedon, baby N. rhombifer for comparison).

7. Adult water snakes are fairly heavy-bodied, but cottonmouths of similar length tend to be significantly stouter. /n/n There are also some notable behavioral differences. Water snakes often bask in branches and bushes overhanging water; this is uncommon in cottonmouths. It is also true that water snakes often swim with the body partially submerged, while cottonmouths usually swim with the head held high and much of the body above the water line, but you can't rely on this characteristic alone; each are fully capable of swimming the other way and sometimes do so. Water snakes are more likely than cottonmouths to dive underwater to escape danger. When approached, water snakes are more likely to rapidly flee, whereas cottonmouths are more likely to slowly crawl away or simply stay still and hope not to be noticed. If approached closely or cornered, water snakes are more likely to flatten out their heads and/or bodies to appear larger and/or strike in the general direction of the person/animal they are cornered by, hoping to create enough space to escape. Cottonmouths, on the other hand, are more likely to tilt their heads back (to a near vertical angle) and gape their mouths open, displaying the white lining of the mouth as a threat display, and vibrate their tails.

Bonus: two separate sets of cottonmouths preying upon water snakes that allow direct comparisons between similarly sized animals, plus a picture of a juvenile cottonmouth (bottom left) with a juvenile common water snake (top) and a juvenile plain-bellied water snake (bottom right).

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