Cottonmouths (Agkistrodon piscivorus) are venomous snakes found across the southeastern United States. They are semi-aquatic reptiles, frequently inhabiting wetlands, swamps, marshes, and the edges of lakes and rivers. This species is often recognized by its unique behavior of opening its mouth wide, revealing a strikingly white interior, which gives them their common name. Understanding this behavior provides insight into their natural responses and clarifies common misconceptions.
The Warning Display
The primary reason a cottonmouth opens its mouth is a defensive warning display. When feeling threatened, the snake will gape its mouth, exposing its stark white, cotton-like lining. This visual signal contrasts sharply with the snake’s typically dark body, serving as a clear message to potential threats, including humans, to retreat. The display indicates the snake feels cornered or stressed and is prepared to defend itself.
This mouth-gaping is not an act of aggression but a bluff, a defensive posture intended to avoid physical confrontation. Cottonmouths prefer to escape or remain still when approached, and they rarely bite unless directly provoked or handled. Studies indicate cottonmouths often attempt to escape or use other threat displays, such as vibrating their tails or releasing musk, before biting. The white-mouth display is a primary component of this defensive repertoire, aiming to deter threats without expending venom.
Other Reasons for Opening the Mouth
While the defensive display is the most recognized reason, cottonmouths also open their mouths for other biological functions. One such behavior is general mouth gaping, sometimes referred to as “yawning.” This is not an indication of tiredness but helps the snake flex or realign its jaws. This jaw adjustment can occur before or after consuming prey, helping the snake prepare for or recover from a large meal.
Snakes also use mouth gaping to enhance their sensory perception. Opening their mouths allows their Jacobson’s organ, a chemosensory organ located in the roof of their mouth, better access to environmental cues. This helps them process chemical information from their surroundings, aiding in detecting prey or understanding their environment. While some reptiles may gape for thermoregulation, such as cooling down, evidence for cottonmouths using this behavior for temperature control is less documented compared to their defensive display or jaw adjustments.
Encountering a Cottonmouth
If you encounter a cottonmouth in its natural habitat, maintain a respectful distance. These snakes are not aggressive and prefer to be left alone. They will not chase people; perceived chasing is usually the snake trying to move towards cover or escape. Giving the snake ample space allows it to retreat without feeling the need to display defensively or bite.
Avoid attempting to handle, harass, or kill a cottonmouth. The majority of venomous snake bites occur when people try to interact with the snake. If you find one in an area where it poses a concern, such as on a porch, slowly back away and allow it to move on its own, or contact professional wildlife control. In the rare event of a bite, seek immediate medical attention and do not attempt to apply tourniquets or other home remedies.