Snakes are reptiles, a group of vertebrates that primarily live on land. The confusion regarding their method of respiration often stems from the existence of aquatic species. The definitive answer to whether snakes have gills is no. Like all other reptiles, snakes use lungs to breathe. This means they must return to the surface to exchange gases with the atmosphere, even those that spend their lives in the water.
How Snakes Breathe
Snakes breathe using pulmonary respiration, drawing air into and expelling it from the lungs using muscle contractions. They lack a diaphragm, the large muscle found in mammals that separates the chest and abdomen. Instead, snakes rely on the muscles between their ribs to expand and contract the rib cage, facilitating inhalation and exhalation.
The internal anatomy of a snake’s respiratory system is adapted to its long, slender body shape. Most species possess only one fully functional lung, which is a single, elongated organ running down much of the body cavity. The left lung is typically greatly reduced or completely absent, appearing as a small, vestigial structure. In many snakes, the anterior section of this primary lung handles gas exchange, while the posterior part is a non-respiratory air sac used for air storage.
A specialized feature that allows snakes to consume very large prey without suffocating is the mobile glottis. This opening to the trachea, or windpipe, can be extended out of the mouth while the snake is actively swallowing. This allows the snake to continue drawing in air even when its mouth is stretched around a large meal. This adaptation is necessary because the digestion process can take a considerable amount of time.
Breathing Strategies for Aquatic Species
The question of gills often arises because some snakes, such as sea snakes and anacondas, are highly adapted to aquatic environments. These air-breathers manage prolonged submersion through a combination of behavioral and physiological adaptations. All aquatic species must eventually surface to breathe.
Sea snakes, for example, can dramatically reduce their metabolic rate while diving, which conserves stored oxygen. They also possess an exceptionally long lung that functions in gas exchange, acts as a large reservoir for air, and aids in buoyancy control. Some species can remain submerged for hours thanks to these internal adjustments.
A less common adaptation in some fully marine snakes is cutaneous respiration, or breathing through the skin. Although the primary method of oxygen uptake remains the lungs, certain sea snakes have highly vascularized skin that allows them to absorb a supplementary amount of dissolved oxygen directly from the water. In some species, this cutaneous gas exchange can account for up to 30% of their total oxygen demand while submerged. Certain species have even been found to have a modified network of blood vessels in their heads that functions similarly to a gill for local oxygen delivery to the brain.
Lungs Versus Gills: A Biological Difference
Lungs and gills represent two fundamentally different biological solutions for extracting oxygen. Lungs are internal organs specifically designed to extract oxygen from atmospheric air. They feature a large internal surface area of tiny sacs, called alveoli, where oxygen diffuses into the bloodstream. This system works efficiently because air contains a high concentration of oxygen.
Gills, conversely, are external or semi-external structures found in aquatic animals, like fish, adapted to extract dissolved oxygen from water. Water contains a much lower concentration of oxygen than air. Gills use a system of filaments and lamellae to maximize surface area, employing a highly efficient countercurrent exchange mechanism. This process ensures that oxygen is continually transferred from the water flowing over the gill surface into the blood flowing in the opposite direction.