Why Do Animals Fast?

Hendro Kusumo Eko Prasetyo Moro, S.Si., M.Sc.

Lecturer at Biology Education Department UAD


Semantically, the word fasting means preventing. The word is generally meant to prevent from drinking, eating, and speaking unnecessary things. Fasting is beneficial for the body, spirit, and social relations. Fasting is not only done by muslims only but also done by other religion believers even by animals. For muslims Ramadhan is the fasting month full of blessings. Then why do animals fast?

According to some sources, elephants, cats, and dogs fast when they are seriously hurt, whereas horses and cows fast when they are sick. Spiders and chicks fast as they are infant as an adaptation process. Salmon, penguins, swans, sea bulls, and seals fast to improve the quality of their sperms and eggs to preduce healthy young generation (Anonymous, 2010; Dadan, 2016). Every animal follows a fasting cycle of which the period varies.

According to Sparks (1983) there is a term hibernation, which can be associated with fasting. During hibernation period some animals sleep for months in the winter. Hibernation reduces animals’ temperature up to 1 degree above the environmental temperature, reduces heart’s beat up to 2% and reduces the oxygen consumption up to 3% (Campbelll, et al.2004). Furthermore, bears, seals, caterpillars, penguins, bats, mice, hedgehog, lizards, flies, bees, insects, and woodchuck fast in their own ways.

Some animals fast for days or for months. Some do estivation or sleep during the summer. This is done due to the rarity of food and prevention of dehydration. The animals doing fasting includes crocodiles, snakes, frogs, dragonflies, aardvarks, lemurs, snails, lungfish, crabs, and slugs. They also fast for different periods of time ranging from days to six years as slugs do (Hickman et. al., 2012). They do fasting for different reasons. They can bear hunger and thirst for months.

Some animals fast under certain conditions. Snakes fast after consuming preys and keep them in their intestines especially when the preys are larger than their bodies. This is because the snakes need much time to digest the preys. They fast for 2 up to 3 weeks. During the fasting snakes do nothing and hide. Sometimes they changes their skins. Fasting makes it easy to change the skins. The raise of temperature because of fasting help them change their skins. At this moment snakes become ‘patient’ not aggressive. After fasting their characteristics and temperament change drastically as the previous characteristics and temperament.

The same case happens to man. Most people return to previous characteristics and temperament after fasting but a few people can retain the characteristics and temperament as they fast.