How Long Can Snakes Go Without Eating? Snake Fasting Explained

Why snakes need so little food

Mammals and birds are endotherms: they turn food into heat to keep a constant body temperature, and that costs a lot. A mouse has to eat a large share of its body weight every day. Snakes are ectotherms that take their warmth from the sun and their surroundings. At rest, a snake uses only a small fraction of the energy that a mammal of the same weight needs.

Body shape and lifestyle help too. Many snakes spend most of their time motionless, coiled in shelter or lying in ambush. They do not chew, so they swallow prey whole, and one big meal can supply a large amount of energy. A python that eats a deer or a pig is taking in a meal that may weigh as much as half of its own body weight, or occasionally more. To see how a snake gets such large prey down, read how do snakes swallow large prey?.

How long different snakes can go without eating

Feeding frequency follows hunting style. Snakes that actively search for small prey eat often, while ambush hunters that wait for big prey eat rarely and can fast for long periods.

These are general patterns, not exact limits. Young snakes grow quickly and need to eat more often than adults. A snake’s body condition at the start of a fast, the temperature around it and whether it is breeding all change how long it can last.

The Burmese python: master of feast and famine

The Burmese python has become the classic animal for studying fasting. In its native range in Asia, it typically eats every month or two, but it can fast for many months, and individuals have been reported going about 18 months without food.

Between meals, its digestive system is shut down to save energy. The stomach shrinks and stops making acid, and the intestines lose much of their mass. After a big meal, everything switches on within hours. In studies led by physiologist Stephen Secor, the python’s intestines roughly doubled in mass within a day or two, and its oxygen use rose to many times the resting level, in the largest meals more than 40 times. The heart’s main pumping chamber can grow by about 40 percent within a few days to deliver the extra blood that digestion needs. A study published in Science in 2011 linked this heart growth to fatty acids that flood the python’s blood after it eats.

After roughly one to two weeks, digestion is complete, and the organs shrink back to their fasting size. The snake has turned a single meal into energy reserves that can carry it through the months ahead.

What happens inside a fasting snake

Researchers have tested snakes’ limits in the laboratory. In a 2007 study, Marshall McCue kept snakes of three species without food for 168 days, about five and a half months. The snakes survived by combining two strategies: they lowered their metabolic rate, in some cases by more than half, and they drew carefully on stored fat and then protein. Some even kept growing in length while losing weight.

Snakes store fat in bands along the inside of the body cavity and in the tail. During a long fast, they use this fat first. Only late in starvation do they start breaking down muscle and other proteins, which marks the real danger zone.

Seasonal and natural fasts

In the wild, long fasts are a normal part of a snake’s year, not just an emergency response.

• Winter brumation. Snakes in Europe, Canada and the northern US stop eating for four to eight months while they wait out the cold in dens. Learn more in do snakes hibernate?.
• Breeding. Males of many species stop feeding while they search for mates, and female pythons usually do not eat during the two to three months they spend coiled around their eggs.
• Shedding. Snakes often refuse food for days to a couple of weeks before shedding their skin, when the old skin clouds their eyes.
• Dry seasons and food shortages. Where prey is seasonal, snakes simply wait, sometimes for months.

Records and limits

Large pythons hold the records for fasting. Besides the Burmese python, the reticulated python, the world’s longest snake, can go many months without a meal after eating a large animal. Reports of snakes surviving two years or more without food exist, but they are mostly anecdotal and hard to verify.

There is an important limit: water. Snakes can survive far longer without food than without water, because they lose moisture through breathing and their skin. In the wild, many snakes drink from puddles, dew or rain, and lack of water is usually the more urgent threat.

Myths and facts

Myth: snakes eat only once a year. Very few snakes eat that rarely by choice. Most eat several to many times a year, and only large ambush hunters sometimes go a year between meals.

Myth: a snake that is not eating is starving. Fasting is normal for snakes in winter, during breeding and before shedding, and healthy snakes are built to handle it.

Fact: some snakes get by on very little. Large pythons and some vipers may survive on just a few big meals a year, a lifestyle no mammal of similar size could manage.