Snakes possess lungs, but their respiratory anatomy and breathing mechanics differ significantly from those of mammals. This specialized system is an adaptation that allows them to thrive despite their elongated, limbless body form and predatory feeding habits. Understanding snake respiration requires looking beyond the familiar mammalian diaphragm to a system built for survival under physical constraints. It is fundamental to maintaining life functions, especially when their bodies are compressed during movement, hunting, or consuming large prey.
Specialized Respiratory Anatomy
The internal arrangement of a snake’s breathing organs relates directly to its long, narrow body shape. Most snakes possess only one functional lung—the right lung—which extends as a single, elongated organ down the body cavity. The left lung is typically reduced or completely absent to accommodate the body’s tubular form.
This single lung is functionally divided into two regions. The anterior vascular lung features a honeycomb-like network of tissue rich in capillaries where gas exchange takes place. The posterior saccular lung is a thin-walled, avascular membrane that acts like an air reservoir or bellows.
The saccular lung does not participate in gas exchange but allows air to be stored and moved efficiently through the vascular lung, especially when the snake is physically constrained. Snakes lack a diaphragm, the muscle that drives breathing in mammals, requiring them to rely on a different mechanism to move air.
The Mechanics of Air Exchange
Air exchange is accomplished through the movement of the ribs and the connecting intercostal muscles. These muscles change the volume of the body cavity. During inhalation, the intercostal muscles contract, pulling the ribs outward and forward to expand the body wall.
This expansion lowers the pressure inside the lung, causing air to rush in. Exhalation is generally passive, occurring when the intercostal muscles relax and the body wall elasticity returns the ribs to their resting position. Other body muscles can also assist in forcing air out.
The saccular lung assists by acting as a pump to move air through the vascular region. Contracting its walls pushes stored air forward into the gas-exchanging area, ensuring continuous airflow. Snakes have a slower metabolic rate than mammals, allowing them to sustain life with a less frequent, rib-driven breathing cycle.
Breathing While Constricting or Swallowing Prey
A snake’s predatory behaviors often involve intense physical compression that would suffocate a mammal, necessitating specialized respiratory workarounds. When a constrictor snake wraps its body around prey, the pressure immobilizes the ribs required for normal breathing. The solution is modular respiration, where the snake shifts the point of ventilation along its body.
If one section of the ribs is immobilized by constriction, the snake activates the intercostal muscles in a different, uncompressed section to draw breath. This allows localized rib movement and lung ventilation to continue uninterrupted in areas not involved in squeezing the prey.
When swallowing a large meal, the prey item can block the throat and obstruct the airway. To overcome this, the snake utilizes its highly mobile glottis, the opening to the trachea. The glottis is located on the floor of the mouth.
As the snake engulfs its meal, it extends this tubular glottis forward, past the food mass, creating a temporary snorkel. This allows the snake to take in air at the front of the mouth, even while the throat is full. This ability to maintain an open airway while consuming prey that can take hours to swallow is a defining adaptation.