The cottonmouth, also widely known as the water moccasin, is a recognizable, heavy-bodied, semi-aquatic snake found in the Southeastern United States. It has a reputation that often precedes it due to its venom and tendency to stand its ground when threatened. The common name, “cottonmouth,” stems directly from a dramatic defensive behavior unique among North American snakes.
The Visual Origin of the Name
The name cottonmouth originates from the snake’s distinctive threat display, performed when it feels cornered or harassed. When preparing to defend itself, this pit viper throws its head back and opens its mouth extremely wide, a behavior called gaping.
The wide-open mouth reveals the lining of its buccal cavity, which is a stark, pale white color resembling cotton. This brilliant white interior creates a high-contrast warning signal against the snake’s typically dark body. The display is purely defensive, serving as an unmistakable visual warning to potential predators to back away.
The snake holds this pose, sometimes accompanied by tail vibration and the release of a musky odor, to deter an intruder without biting. This gaping behavior is not a prelude to an immediate strike, but a clear signal that the animal is highly agitated and prepared to defend itself. The dramatic nature of this defensive posture cemented the common name “cottonmouth” across its range.
Scientific Identity and Related Species
Formally, the cottonmouth is recognized as Agkistrodon piscivorus (or Agkistrodon conanti for the Florida species). The species belongs to the family Viperidae, specifically the subfamily Crotalinae, which includes all New World pit vipers.
This classification places the cottonmouth in the same genus, Agkistrodon, as the copperhead (A. contortrix). Both species are close relatives and share the general morphology and venom-delivery system characteristic of pit vipers. The family also includes all species of rattlesnakes. The specific epithet piscivorus is Latin for “fish-eater,” referencing the snake’s semi-aquatic nature and diet.
Key Identification Markers and Range
The cottonmouth is the world’s only semi-aquatic pit viper. It is found throughout the swamps, marshes, and slow-moving bodies of water across the Southeastern United States. Its range extends from southeastern Virginia, through the Carolinas and Florida, and west to eastern Texas and the Mississippi River Valley.
Physically, the cottonmouth is a heavy-bodied snake with a thick, distinctly blocky or triangular head, which is noticeably wider than its neck. Like all pit vipers, it possesses a deep, heat-sensing loreal pit located between the nostril and the eye. Its pupils are vertically elliptical, resembling a cat’s eye. A dark stripe often runs from the eye to the back of the jaw.
Cottonmouths are often confused with harmless water snakes (Nerodia species) that occupy the same habitat. A reliable field difference is that the cottonmouth often swims with its body mostly floating on the water surface. Non-venomous water snakes typically swim with only their heads above the surface. Furthermore, when viewed from above, the cottonmouth’s eyes cannot be seen because of the overhanging scales.