Snake Digestion: What a Snake Eats
Although snake species have different methods of finding and catching prey, all snakes eat in basically the same way. Their amazingly expandable jaws enable them to prey on animals of much larger size -- and swallow them whole. Whereas the upper jaw of a human is fused to the skull and therefore unable to move, a snake's upper jaw is attached to its braincase by muscles, ligaments and tendons, allowing it some front-to-back and side-to-side mobility. The upper jaw connects to the lower jaw by the quadrate bone, which works like a double-jointed hinge so the lower jaw can dislocate, allowing the mouth to open as wide as 150 degrees. Also, the bones that make up the sides of the jaws are not fused together at the front like the human chin, but instead are connected by muscle tissue, allowing the sides to separate and move independently of one another. All of this flexibility comes in handy when a snake encounters prey bigger than its head -- its head can stretch to accommodate it.
Once a snake is ready to eat, it opens its mouth wide and begins to "walk" its lower jaw over the prey as its backward-curving teeth grip the animal -- one side of the jaw pulls in while the other side moves forward for the next bite. The snake drenches the prey with saliva and eventually pulls it into the esophagus. From there, it uses its muscles to simultaneously crush the food and push it deeper into the digestive tract, where it is broken down for nutrients.
Even with all of these advantages, eating a live animal can be a challenge. Because of this, some snakes have developed the ability to inject venom into prey to kill or subdue the animal prior to eating it. Some venom even gives the digestion process a kick-start. Snakes with this effective tool must have an equally effect way of getting the poison into an animal's system: fangs.
At the front or back of their upper jaw, venomous snakes have two sharp teeth that are hollowed out to allow the poison to pass through. Once a snake strikes, inserting these teeth into its prey, venom is squeezed from a gland under each eye into the venom duct -- where it passes more glands that release compounds thought to make the venom more effective -- and out through the venom canal in the fangs.
In non-venomous, constrictor snakes, the teeth are stationary; in snakes with long (grooved) fangs, the teeth fold backward into the mouth when not in use -- otherwise, the snake would puncture the bottom of its own mouth.
Although the venomous snake species -- which make up only one fifth of all snakes -- each have their own special brew, the following are the three most important types of toxins found in snake venom:
- Neurotoxins - Affect the nervous system by seizing up the nerve centers, often causing breathing to cease
- Cardiotoxins - Deteriorate the muscles of the heart, causing it to stop beating
- Hemotoxins - Cause the blood vessels to rupture, resulting in widespread internal bleeding
Some venom may also include agglutinins, which make the blood clot, or anticoagulants, which make the blood thin. Most snake venom makes use of several of these compounds for a deadly combined effect. A few snakes squeeze the life out their prey in another way -- constriction. Once a snake has the animal firmly in the grip of its jaws, it loops its body in coils around the prey. When the animal exhales, letting the air out of its body cavity, the snake contracts its powerful system of muscles to tighten the coils, squeezing the body so that the animal cannot breathe in again. According to a Carnegie Mellon University study in 2002, depending on its size, a constrictor can apply 6 to 12 pounds of pressure per square inch. Although this pressure suffocates the prey by compressing the lungs, it can also have the same effect on the heart, speeding up death significantly.