Many snake species are surprisingly capable swimmers, an ability more widespread than commonly perceived. Snakes enter water for various reasons and exhibit different levels of proficiency, allowing them to thrive in diverse environments, from oceans to backyard ponds.
The Aquatic World of Snakes
Snakes can be categorized into three groups based on their aquatic lifestyle. Fully aquatic snakes, such as true sea snakes, have evolved specialized adaptations for life in marine environments. These include paddle-like tails, sealable nostrils on top of their heads, salt glands to excrete excess salt, and some exhibit cutaneous respiration, absorbing oxygen through their skin.
Other snakes are semi-aquatic, spending significant time in or near water but also moving on land. This group includes many North American water snakes (Nerodia) and cottonmouths (Agkistrodon piscivorus). Sea kraits (Laticauda spp.) are also semi-aquatic, returning to land to lay eggs, unlike true sea snakes that give birth to live young at sea. Garter snakes (Thamnophis spp.) are another common example, often found near ponds and streams.
Even many terrestrial snakes can swim when needed. Land-dwelling species like rat snakes and copperheads can readily enter water for various purposes. This capability allows them to navigate watery obstacles or or access new resources.
How Snakes Navigate Water
Snakes propel themselves through water primarily using lateral undulation, an S-shaped movement with their bodies. This serpentine motion pushes against the water, generating thrust. The flexibility of their long, muscular bodies allows for efficient aquatic movement.
Many aquatic species have physical adaptations for swimming. True sea snakes, for instance, have distinctly flattened, paddle-like tails that act like rudders for propulsion. Their bodies are often laterally compressed, aiding movement. Some sea snakes can even sense light with their tails, which may help them avoid predators.
Snakes also employ buoyancy control to navigate vertically. They use their single elongated lung, which extends nearly the entire length of their body, to adjust buoyancy, allowing them to float or dive. Some sea snakes can remain submerged for several hours, absorbing oxygen through their skin to supplement lung capacity.
Why Snakes Take to Water
Snakes venture into water for various reasons. A primary motivation is hunting, as many species prey on aquatic animals like fish, frogs, and salamanders. Water provides a rich hunting ground for these opportunistic predators.
Water also serves as an effective escape route from land-based predators. When threatened, snakes can quickly dive into water, using it as a refuge. Additionally, snakes may use waterways for migration, to travel to new habitats, find mates, or access dispersed resources.
Thermoregulation is another reason snakes enter water, as it helps manage their body temperature. On hot days, water offers a cooler environment, while basking on rocks or logs near water allows them to warm up. Some snakes may also soak in water to aid in the shedding process.
Identifying Common Swimming Snakes
Distinguishing between different swimming snakes is important, especially given the presence of venomous species. A key behavioral difference is how snakes float: venomous cottonmouths tend to swim buoyantly with much of their body visible, while non-venomous water snakes typically swim mostly submerged, showing only their head and back. However, this guideline is not always foolproof.
Cottonmouths, also known as water moccasins, have a thick, blocky head distinctly wider than their neck, giving it a triangular appearance due to venom glands. They possess vertical pupils and a dark stripe through the eye. When threatened, they may display the white interior of their mouth, giving them their common name.
Non-venomous water snakes, in contrast, have a more slender head that blends smoothly into their body and round pupils. Their bodies are also more slender and their tails longer and thinner than cottonmouths.
Garter snakes, common in many regions, are proficient swimmers, often keeping their heads above water with a wriggling motion. Sea snakes are easily identified by their flattened, oar-like tails and nostrils positioned dorsally on their snout.
Always maintain a safe distance from any snake. Observing snakes from afar is the safest approach, as identification can be challenging, and even non-venomous snakes can bite if provoked.