Snakes can and do bite underwater, but the likelihood and mechanics depend highly on the species and the circumstances of the encounter. The ability to strike and envenomate prey or a threat while submerged demonstrates the evolutionary adaptability of these reptiles. Understanding the biological limitations and behavioral context helps demystify the risk associated with aquatic snakes.
The Physical Capacity for Submerged Biting
The primary challenge a snake faces when biting underwater is the density of the fluid, which is about 800 times greater than air, significantly impeding movement. This high drag means a snake’s strike velocity and accuracy are constrained compared to a strike on land. Aquatic foraging snakes have evolved specific head shapes that are proportionally narrower at the front than non-aquatic species, which helps reduce hydrodynamic drag during a forward strike.
A snake’s jaw structure, which includes loosely connected bones and an elastic ligament at the chin, allows for a wide gape maintained during an underwater strike. To prevent water from rushing into the lungs during an open-mouthed strike or while struggling with prey, the snake possesses a highly mobile, tubular structure called the glottis. This glottis, the opening to the trachea, can be extended forward and positioned against the side of the mouth, functioning like a biological snorkel to allow the snake to breathe air at the surface even while its mouth is submerged or full.
The physical strike is less about speed and more about efficiency in an aquatic environment. A fast strike underwater can create a bow wave of displaced water in front of the head, which can inadvertently push smaller prey items away from the snake’s mouth. Aquatic snakes often compensate by striking at prey from a very short distance, reducing the time the prey has to detect the pressure change and initiate an escape reflex.
Sea Snakes vs. Freshwater Species: A Behavioral Difference
The capacity for submerged biting varies significantly between fully marine species and semi-aquatic freshwater snakes. True sea snakes (Elapidae family) are fully adapted to ocean life and perform all feeding and mating entirely underwater. These venomous reptiles possess adaptations like flattened, paddle-like tails for efficient swimming and specialized salt glands beneath the tongue to excrete excess salt.
These marine species are efficient underwater hunters, relying on quick, predatory strikes on fish and eels. Conversely, semi-aquatic freshwater snakes, such as the cottonmouth (water moccasin) and various non-venomous water snakes, spend time both in and out of the water. Although capable of biting submerged, their underwater movements are less streamlined than their marine counterparts.
Freshwater species often hunt by ambush from the water’s edge or by seizing slow-moving prey. For humans, encounters with freshwater snakes are typically defensive actions triggered by a perceived threat, such as being closely approached or accidentally stepped on in shallow water. Sea snakes, despite their potent venom, are generally docile, and most bites occur when they are accidentally disturbed in fishing nets or stepped on by waders.
When and Why Submerged Bites Occur
A snake will only bite underwater for two primary reasons: to secure a meal or to defend itself from a perceived threat. Predatory strikes are typically quick, purposeful actions aimed at subduing prey like fish or eels. These bites are often efficient and focused on securing the animal.
Most human-snake encounters that result in a bite are defensive reactions. When a snake is surprised, cornered, or physically touched, it responds with a defensive strike. For example, a high percentage of sea snake bites occur on the lower limbs, suggesting the snake was accidentally stepped on or disturbed in its environment.
Defensive bites are not always the snake’s first reaction; they will often try to flee if given the opportunity. If escape is not possible, a snake may resort to a threat display before biting, as striking is costly in terms of energy and risk. The snake views the human not as a food source, but as a large, immediate danger that must be repelled.
Safety Measures and Encounter Avoidance
Caution in aquatic environments where snakes are common is the most effective way to prevent a submerged bite. Since most bites occur when a snake is accidentally disturbed, avoid walking through murky water where visibility is poor. If you cannot see the bottom, you risk stepping on a resting or camouflaged snake.
When wading or swimming near banks, logs, or thick vegetation, remember these areas are common resting and hunting spots for semi-aquatic species. Never attempt to handle, harass, or pick up any snake, even if it appears dead, as reflexes can sometimes remain active after death. Give any snake you encounter a wide berth and slowly move away to allow it space to escape.