How Do Snakes Swallow Large Prey? Jaws That Stretch

A skull built to stretch

Most animals, including people, have a tightly built skull and a lower jaw made of a single bone hinged directly to the skull. A snake’s head works very differently:

• The lower jaw is in two halves. In mammals the two sides of the lower jaw are fused at the chin. In snakes they are separate and joined only by an elastic ligament, so they can spread apart sideways to widen the mouth.
• There is an extra hinge. Each half of the lower jaw connects to the skull through a long, movable bone called the quadrate. This works like a second hinge, letting the back of the jaw swing outward and downward to open the gape far beyond what a simple hinge allows.
• The upper jaw bones move too. The bones that carry the upper teeth, along the edge of the mouth and on the roof of the mouth, are loosely attached to the braincase and can move forward, back and sideways independently.

Snakes are called “gape-limited” predators because the widest prey they can eat is set by how far this flexible skull can stretch, not by the size of their teeth or stomach. Large constrictors such as the reticulated python and the Burmese python have especially long quadrate bones and very wide gapes.

The “jaw walk”: how a snake pulls itself over its meal

A snake does not suck its food in or push it down with its throat at first. Instead it moves its head over the prey. The left and right sides of the jaws take turns: one side holds the prey while the other side lets go, slides forward and bites down again a little farther along. Then the sides swap.

Herpetologists sometimes call this the “pterygoid walk”, after one of the toothed bones on the roof of the mouth. With each step the snake inches its head over the prey, a bit like pulling a sock onto a foot. The sharp, backward-curving teeth make the process work: they slide easily forward but grip strongly against any movement backward, so the prey can only go one way.

Once the prey reaches the throat, the snake bends its neck and body in waves and uses powerful muscles to push the meal down toward the stomach. Large snakes usually swallow prey head first, so that legs, fur and feathers fold back neatly instead of catching.

Stretchy skin and no breastbone

Getting the prey past the jaws is only the first challenge. It must also travel through the body. Snakes have no breastbone, and their ribs are not joined at the front, so the ribs can spread apart as a large meal passes. The skin between the scales is soft and elastic and stretches so much that the scales of a full snake may stand well apart. For more on the skeleton that makes this possible, see do snakes have bones?

Breathing during a long meal

Swallowing a big animal can take an hour or more, and with its mouth crammed full a snake might seem to have no way to breathe. The answer is the glottis, the opening of the windpipe. In snakes it sits far forward on the floor of the mouth and can be pushed out beyond the edge of the prey, like a snorkel, so air can still flow in and out.

Constriction and swallowing also squash parts of the body. Research on boa constrictors published in 2022 showed that a snake can shift its breathing movements to a different section of its rib cage when one section is pressed by coils or filled by a meal. This flexible breathing may have been one key to the evolution of very large prey in snakes.

Myth: snakes unhinge or dislocate their jaws

It is often said that snakes “unhinge” or “dislocate” their jaws to eat. They do not. The joints never come apart. What looks like a dislocated jaw is the normal action of the loosely joined skull, the stretchy chin ligament and the swinging quadrate bones. When the meal is down, a snake often yawns widely a few times, which appears to settle the jaw bones back into their resting positions.

Records of huge meals

Giant pythons hold the records for large prey. Big reticulated pythons regularly eat wild pigs and deer, sometimes heavier than 60 kg (130 lb), and are thought to be able to swallow prey up to about their own weight. A 6.95 m (22 ft 10 in) python in Indonesian Borneo swallowed a 23 kg (51 lb) sun bear and took roughly ten weeks to digest it. Burmese pythons in Florida have eaten white-tailed deer and even alligators.

The smaller egg-eating snakes of Africa are just as remarkable. They swallow bird eggs about three times the width of their own heads, then crack them with bony spikes in the throat and spit out the shell. In rare cases large pythons also take very big prey such as people, as explained in can a snake eat a human?

What happens after a big meal

A large meal sets off dramatic changes inside a python. Studies of Burmese pythons have found that after eating, their metabolic rate can rise around 40-fold, the intestines grow larger, and the heart can increase in mass by about 40 percent within a few days, before everything shrinks back once digestion ends. A big snake may then go weeks or months before eating again; see how long can snakes go without eating?