The Water Moccasin, commonly known as the Cottonmouth (Agkistrodon piscivorus), is a venomous, semi-aquatic pit viper found throughout the southeastern United States. This snake inhabits marshes, swamps, lakes, and other wetland areas. Accurate identification is necessary for anyone living or recreating in its range, as it is the only venomous water snake in North America. The moniker “Cottonmouth” originates from the bright white lining of its mouth, which it displays as a clear warning when threatened.
Key Physical Identification Traits
The most reliable visual trait of the Cottonmouth is its head structure, which is distinctly triangular and blocky. This appearance is created by the large venom glands located on the sides of the head behind the eyes, giving it a prominent jowl-like look. The neck appears noticeably narrower than the head, unlike most non-venomous snakes whose heads blend more smoothly into their bodies.
As a pit viper, the Cottonmouth possesses heat-sensing pits located between the eyes and the nostrils. Its pupils are vertically elliptical, resembling a cat’s eye slit in daylight, a feature shared by other nocturnal pit vipers. Non-venomous snakes in the region generally have round pupils.
The body of the Cottonmouth is heavy and thick for its length, typically ranging from 30 to 48 inches long, and covered in strongly keeled scales that give it a rough texture. Coloration ranges from dark brown, olive, or banded patterns in younger snakes to a uniform, unpatterned black in many adults. Juvenile Cottonmouths often exhibit a high-contrast pattern and a bright, sulfur-yellow tail tip, which they use to lure small prey.
Distinctive Behavioral Markers
When disturbed, the Cottonmouth performs a defensive posture. It will coil its body and throw its head back, opening its mouth widely to reveal the stark, white interior—the source of its common name. This is a clear warning display, and the snake will often hold this gape for a prolonged period.
The snake also vibrates its tail rapidly when alarmed, which can create a rustling sound if done in dry leaves or debris. When swimming, the Cottonmouth is buoyant and rides with its entire body on the surface of the water, with only its head slightly submerged.
Cottonmouths are often observed basking in the sun on logs, stumps, or low-hanging branches overhanging the water. They are generally reluctant to flee and will often stand their ground with a defensive posture instead of quickly retreating.
Avoiding Misidentification: Common Look-Alikes
The primary source of misidentification is the harmless Water Snake (Nerodia genus), which shares the Cottonmouth’s affinity for aquatic habitats and general dark coloring. Water Snakes lack the heavy, blocky head and narrow neck distinction characteristic of the Cottonmouth. Their eyes have round pupils and they do not have the heat-sensing facial pits.
A Water Snake’s defensive behavior can cause confusion, as many species will flatten their heads and bodies when threatened to mimic the triangular shape of a viper. Even when flattened, the Water Snake’s head does not possess the same massive jowls, and the neck-to-head transition remains less defined. When swimming, Nerodia species typically keep only their head and a small portion of their neck above the water, with the rest of their body submerged.
Water Snakes are known to be aggressive when cornered or handled and will bite readily, but their bite is non-venomous. Differentiating between the two species is crucial. The pattern of dark crossbands on Nerodia is usually widest along the back, while on a Cottonmouth, the dark bands are typically narrowest at the top of the back.
Encounter Safety and Prevention
If a snake is identified or suspected to be a Water Moccasin, maintain a distance of at least six feet. Never attempt to approach, handle, harass, or kill the snake, as most bites occur when a person actively engages with the animal. Wearing thick, high leather boots when walking in swampy or wooded areas can provide a layer of protection against a strike.
When moving through habitats where they are present, watch where you place your hands and feet, particularly around logs, dense vegetation, and rock piles. Cottonmouths are frequently active at night, so using a flashlight when walking after dark is a sensible precaution.
Should a bite occur, seek professional medical attention by calling emergency services. Keep the bitten extremity immobilized and at a neutral level, or slightly below the heart if possible, to slow the spread of venom. Remove any jewelry or tight clothing from the affected limb before swelling begins. Do not use a tourniquet, apply ice, cut the wound, or attempt to suck out the venom, as these actions are ineffective and can cause further tissue damage.