The cottonmouth, also known as the water moccasin, is the only venomous water snake found in North America. Identifying this snake is important for safety, yet its appearance changes dramatically from birth to adulthood. Juvenile cottonmouths look significantly different from their parents, often leading to confusion with non-venomous species. Recognizing the specific markings and features of a young snake is key to accurate identification.
Identifying Juvenile Cottonmouths: Key Features
The pattern and coloration of a newly born cottonmouth are more vivid than those of a mature adult. The juvenile’s body features a lighter background color, ranging from pale tan or gray to reddish-brown. Prominent dark crossbands run along the body, often described as blocky or hourglass-shaped. These bands may contain dark spots and speckles within the lighter centers, making the pattern sharply defined.
A defining characteristic of the juvenile is the bright sulfur-yellow or greenish tail tip. This appendage is actively wiggled by the young snake in a behavior called caudal luring. The movement mimics a small insect or worm to attract prey like frogs and lizards within striking distance. Newborns are relatively small, often around 9 to 10 inches in length, but they possess a distinctly large, triangular head relative to their body size.
The head displays several features common to pit vipers, even at a young age. A broad, dark stripe runs from the eye to the angle of the jaw, camouflaging the eye within this band. Like all pit vipers, they possess a heat-sensing pit organ located between the nostril and the eye. The pupils are vertically elliptical, resembling a cat’s eye.
Changes in Appearance as They Mature
The bright, contrasting pattern of the juvenile cottonmouth is temporary and begins to fade as the snake grows. The distinct, hourglass-shaped crossbands gradually lose their sharp definition. The lighter background color darkens significantly, often becoming a deep olive, brown, or nearly black shade. This darkening process can make older cottonmouths appear uniformly dark, obscuring the original pattern completely.
The bright yellow or greenish tail tip is one of the first features to disappear, fading to a duller color or black within the first year of life. This change corresponds with the cessation of the caudal luring behavior, as the snake shifts to a different hunting strategy. The head remains characteristically wide and blocky due to the venom glands. Adults typically reach an average length between 30 and 48 inches.
Practical Identification: Differentiating from Similar Species
Misidentification often occurs when juvenile cottonmouths are confused with non-venomous water snakes, particularly those in the Nerodia genus. A key distinction is the pattern of the crossbands on the body. Juvenile cottonmouth bands are widest on the sides and narrowest across the back, giving them the distinctive blocky shape. Conversely, the dark bands on Nerodia species are widest on the top of the back and narrow toward the sides, creating a different visual impression.
A second difference is the snake’s posture when swimming. Cottonmouths are naturally buoyant and typically swim with their entire body floating high on the surface. Water snakes, however, are less buoyant and tend to swim with most of their body submerged. Only their head and a small portion of their neck are visible above the water line. This difference in swimming style is often the easiest field identification method.
Non-venomous water snakes can flatten their heads when threatened to mimic the cottonmouth’s triangular shape. However, a cottonmouth’s head is notably thicker than its neck, while a water snake’s head, even when flattened, remains less distinct. The presence of the dark facial stripe and the vertical pupils are also useful distinguishing characteristics that water snakes lack.