How to swallow something bigger than your head
Swallowing success: Having a narrow body and small head, and no limbs and chewing teeth, snakes have to swallow their prey whole. Their success and huge diversity is partly due to their ability to swallow very large prey relative to their size. Most can eat up to 20% of their body weight in one sitting, some equal to or more than their own body weight!
How does a snake swallow something much bigger than its head? Several snake features allow this feat, equivalent to a human swallowing a whole watermelon.
Highly expandable mouth: A snake's jaws are only loosely joined to its skull by ligaments which are very strong--so the jaws act as one solid structure during the bite--but flexible enough so the structure can dislocate and expand greatly when it's time to swallow. Also, parts of their skulls are reduced, allowing more flexibility.
The quadrate bone (coloured orange) works like a double-jointed hinge. That is, the lower jaw dislocates from the upper jaw, allowing snakes to open their jaw up to 150 degrees (ours can open only 45 degrees). Also, the front portion of the lower jaws can separate, and the quadrate bone hinge allows the lower jaws to swing apart. The snake resets its jaws by yawning-like movements. Some snakes (e.g., blindsnakes) which cannot dislocate their jaws can eat only small prey.
How big a prey can a snake eat? It is the diameter of the prey and not its weight that limits their edibility to snakes. Some snakes can't open their mouths very wide because their skulls are more solidly fused together, e.g., blindsnakes which can only eat soft or thin prey like worms and insect larvae.
Vipers are able to open their mouths the widest and eat the heaviest prey relative to their weight. While a large python is only able to eat prey less than 50% its body weight, a viper may be able to eat one 150% of its weight! It is believed that because viper venom is so toxic, they can kill prey efficiently without having to have a solid bite like the constrictors. This means their jaws can be more loosely joined to the skull and thus they can expand their mouths wider. Using teeth to "walk" over prey: The right and left halves of the upper and lower jaws can move independently. To move the prey into the gullet, the snake moves the right side of its upper and lower jaws forwards, then the left side, in alternate movements, gripping the prey with its normal teeth. To give an analogy, it is as if you were lying on your belly and moving over an object on your elbows. Many snakes have a double row of teeth on the upper jaw (see diagram above) to help grip the prey as it "walks" over it.
Expandable skin and insides: The skin between around the mouth and neck is highly elastic. The gullet (oesophagus) is pleated allowing expansion. The gullet and stomach are almost the same diameter and have strong muscles to move prey into the body. Breathing even with its mouth stuffed with food: Unlike other animals, which have the opening to the trachea (glottis) deep inside the mouth, in most snakes, this can be protruded to the edge of the mouth. Although many snakes can hold their breath, it often takes a while for prey to get past the mouth, sometimes more than an hour.
Powerful digestive enzymes: Snake saliva not only eases swallowing by lubrication, but also contains powerful enzymes to break down tissues and even egg shells. But snakes generally cannot digest keratin (claws, hair) or chitin (arthropod exoskeleton). Many prey are covered with tough hide and if a snake relied solely on its digestive juices, it would take a long to time to get through to the nutrients. So this is speeded up by snake venom. Venom not only immobilises prey but also starts digesting the prey from the inside. A study showed that when a fer-de-lance (Bothrops asper) is deprived of its venom it took 12 days to digest a rat instead of the usual 2-3 days.
Other features: The skull is protected by a strong bony box to prevent struggling live prey from damaging the brain.
More about eating: To speed up digestion, snakes will raise their body temperature after swallowing prey. They do this by choosing warmer snoozing places (under a hot flat rock) or sticking out the body coil containing the prey into the sun. The ideal digestion temperature is 30 degrees C. If it falls below 10 degrees C, most snakes will regurgitate the prey as it cannot digest the prey before it rots. Because a snake is less mobile with large prey in its body, if it is disturbed while digesting, it may also regurgitate the prey. Hibernating snakes are nourished by their store of glycogen in their liver; if they don't eat enough before hibernation, they can starve to death in their slumber.
Snakes will usually swallow prey head first where this eases swallowing (direction of fur, limbs), but may swallow tail first for the same reason, eg. for crayfish. In the wild, snakes rarely fight over food (though they do fight over mates). It can be dangerous to steal each other's food: one captive snake swallowed another snake because they were both swallowing the same prey from either end. One snake got swallowed together with the prey.
More about snakes
- What are snakes?
- Are snakes cold?
- Why are snakes long?
- What do snakes eat? Do they drink?
- How do snakes swallow?
- How do snakes hunt?
- Why and how do snakes kill?
Snake predators and how do snakes protect themselves?
Snake mating, eggs and babies
Where are snakes found?
Fascinating snake adaptations to various habitats
Snake bites and first aid
Snakes in danger: role and conservation and snakes in human culture
Snake records: biggest, smallest, deadliest and more
- More snakes
- More animals
- General snake links and references
Further informations in german can be found here!