Animals and body heat : how they survive

Leo Garnier

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Most living beings emit body heat. That heat allows organs to function. But some cold-blooded animals function differently. How do these survive?

In the animal and human kingdoms, body heat is an indication of life. Heat preserves our organs and allows our bodies to function. The cold hurts us because it slows down our metabolism, to a point where it can kill us (hypothermia).

The different types of body heat conservation are very in depth. As such, we will not get too much into detail, for the sake of keeping this article readable.

Humans and hot-blooded animals

High body temperature is one of the most important factors of survival. But we’re so used to heating and comfort that we forgot how important it is for life. Things haven’t changed in the animal kingdom though.

Organisms such as humans, that maintain a constant body heat, are usually called endotherms.

An example of endothermy. Ostrich maintain their body heat at around 12°c.
An example of endothermy.

These organisms produce their own body heat through the consumption of energy. Our own body temperature is 37°C, and it is kept that way by burning calories. But the heat that our body emits can be impaired by excessive cold or heat, and in these cases, we have to find ways to regulate it. Either by taking shelter or using water to cool ourselves off.

This is what we usually refer to as “hot blooded”. Animals and humans with a high body temperature that will be warm to the touch. The appellation “hot-blooded” simply comes from the fact that our blood, like our entire body, remains at a high temperature.

A shift too important in body heat can kill us. An excessive cold will stop the function of the vital organs that will go comatose, and excessive heat will do the opposite, sending the organs into an “overdrive” state that will be unsustainable for the body.

Cold-blooded animals

But not everything in the kingdom of life emits heat. You probably know it already, but some animals are known for being “cold-blooded”. These are often called ectotherms. These animals, unlike us endotherms, do not produce their own body heat. They’re like cold moving statues and are cold to the touch.

Snakes can withstand extreme heat thanks to their cold by temperature.
Snakes can withstand extreme heat thanks to their cold by temperature.

Let’s take snakes as an example. They do not emit any heat and tend to live in extremely warm environments. These include, but are not limited to, deserts, rainforests, tropical jungles… The absence of body heat allows them to survive temperatures that would otherwise be too extreme.

But to get that body heat during normal temperatures, they have to stay in the sun as much as possible. This, in turn, makes them vulnerable to predators. (This is why snakes have generally intimidating appearances and camouflaged scales: they blend into the environment or scare predators away.) They’re also extremely vulnerable to cold temperature.

Chameleons, lizards, iguanas… The majority of reptiles are cold-blooded and use external sources of heat to function.

This adaptation method has several pros & cons: since these organisms don’t need to burn calories to sustain themselves, they rarely need to eat. Most reptiles can go unfed for several weeks.
On the other hand, endothermy makes organisms “slow”. Despite having scary reaction times in case of danger, endotherms are usually quite slow in their movements, which makes them vulnerable.

The absence of heat in their bodies reduces their physical reactions, which makes them easy prey. Reptiles are especially weak at night, and they usually hide in burrows at that time.

The inbetweeners

Poikilothermia is the third biggest category of body heat regulation. Poikilotherms are animals that change their body temperature during certain times of the year. This category includes certain types of reptiles and batrachians such as frogs. Frogs can regulate the temperature of their body according to the place where they are.

Hibernating animals are the clearest example of poikilothermia. Animals such as bears will hibernate for long periods of time. During these periods, their body heat can drop down to the negatives. Requiring almost no food at all, this fascinating process allows these animals to survive only by sleeping in a comatose-like state for months.

Bears can survive the cold months of winter by lowering their own body temperature.
Bears can survive the cold months of winter by lowering their own body temperature.

There are many important factors to the survival of living beings, but one of them is always constant: heat means life to all living species. Life can slow itself down, almost coming to a stop during extreme colds, but will always return along with the heat.

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Leo Garnier