Snakes often spark questions about their relationship with water, particularly whether they can breathe underwater. While they cannot, many species have developed remarkable adaptations to thrive in aquatic environments.
The Truth About Underwater Breathing
Snakes, like all reptiles, are air-breathing vertebrates equipped with lungs, not gills. They cannot extract dissolved oxygen from water. Their respiration relies on atmospheric oxygen, which they take in through their nostrils. When submerged, snakes must hold their breath.
A snake’s respiratory system features a single functional, elongated lung in most species, though some, like boas and pythons, have two. Unlike mammals, snakes lack a diaphragm and instead use muscles between their ribs to expand and contract their lungs for breathing. The front part of their lung is where gas exchange occurs, while the rear portion often functions as an air sac, storing air for periods when breathing is difficult or impossible.
How Snakes Adapt to Aquatic Environments
Many species exhibit specialized adaptations that allow them to spend extended periods submerged. A primary adaptation is their ability to hold their breath for considerable durations, often for several minutes, or even hours for some aquatic species. Their elongated lung, particularly the air sac portion, can serve as an oxygen reservoir, helping them conserve oxygen during dives. Some aquatic species also possess a larger, more functional left lung which can aid in hydrostatic purposes, helping them control buoyancy in water.
Snakes can also slow their metabolic rate, a process known as bradycardia, which reduces their oxygen demand and extends their underwater time. Their nostrils are often positioned dorsally (on top of the snout) and can be sealed with specialized valves to prevent water from entering during submersion. Additionally, an adaptation found in many aquatic snakes, particularly sea snakes, is cutaneous respiration. This involves absorbing some oxygen directly from the water through their skin. While not sufficient for all their oxygen needs, this skin breathing can supplement lung respiration and contribute significantly, sometimes up to 25-33% of their oxygen requirements, allowing for prolonged dives.
Diverse Aquatic Lifestyles of Snakes
Snakes demonstrate a wide range of aquatic lifestyles, from those that occasionally enter water to highly specialized marine species. True sea snakes, belonging to the subfamily Hydrophiinae, are extensively adapted for life entirely in marine environments. They possess paddle-like tails and often have laterally compressed bodies, which enhance their swimming efficiency. Their nostrils are typically located high on the snout and have valves to seal them underwater. Many sea snakes also have specialized salt glands, often located under or around the tongue sheath, to excrete excess salt ingested from seawater. These adaptations allow them to stay submerged for several hours, with some species observed remaining underwater for up to two hours on a single breath, supplemented by cutaneous respiration.
In contrast, freshwater aquatic snakes, such as various species of water snakes (genus Nerodia), are common in rivers, lakes, ponds, and marshes. They are excellent swimmers, spending considerable time in water for hunting and evading predators, but are not as specialized for prolonged submersion as true sea snakes. These snakes typically surface more frequently to breathe and may bask on rocks or branches near the water’s edge. Their streamlined bodies and scales reduce friction, aiding efficient movement through water. They primarily feed on fish and amphibians, using their aquatic skills to capture prey.