An Idiot’s Guide To Warm And Cold-Blooded Animals

I’m sure that they teach you the difference between warm and cold-blooded animals at school, right? I assume they do. However, for some of you, good folks at home school was a long time ago! So for those of you sat there scratching your head here is a simple explanation so you can impress…actually, nobody will be impressed.


Fundamentally the difference between being warm and cold-blooded is that if you are warm-blooded your internal temperature stays the same regardless of what the temperature outside is. You know, roughly speaking! I mean if you go swimming in the Arctic seas in a pair of speedos your core temperature is going to dip but in general, you will stay the same within a range of fluctuations. Cold-blooded animals do not regulate their own temperature and it is affected by their environment. But it’s far more complex than that.


Mammals are a classic example of warm-blooded animals. In order to maintain our inner temperature, we have developed several strategies. Firstly we eat a lot. Look at Panda bears that literally spend at least 10 hours a day feeding in order to maintain themselves. This food is a source of energy which our body uses to produce heat, but what if we get too hot? That is why mammals sweat to reduce their heat.

Reptiles and fish are examples of cold-blooded animals. When it is warm outside these animals will soak up the heat and raise their body temperature. When it gets cooler they may shiver, hibernate or brumate or simply move to a warmer area.

ectothermic vs. endothermic

Remember how I said it wasn’t as straight forward as you might think? Buckle up it’s about to get complicated. While at school we are taught animals are either warm or cold blooded they are actually divided up into a slightly more complex system. Animals can either regulate their own temperature or rely on external factors to regulate it. If they are able to self-regulate they are endothermic and if they need their environment they are ectothermic.

Poikilothermic vs. Homoeothermic

And to further complicate matters some animals are okay with having a varying core temperature. These animals are referred to as being Poikilothermic whereas some animals need a consistent core temperature and these are Homoeothermic. Is your brain hurting yet? Don’t worry we are past the hardest part…or are we?


Scientists used to assume that Dinosaurs were all cold-blooded killers stomping around in the hot Triassic sun. Well perhaps not. Given their size and other evidence scientists now believe they may have been mesotherms. This is a halfway house between being ectothermic and endothermic. So basically they got some of their heat from the environment but also had internal systems to regulate their body heat to an extent.

What this means

Well, temperature affects muscles. Because of this, creatures that rely on the environment for their heat will always be more sluggish when it is cold. However, having a system that regulates your temperature comes with a cost. We have to eat, a lot. Some mammals can’t go for more than a week or two without a meal whereas some ectotherms can wait up to a year to eat. So you may think that this gives cold-blooded animals an advantage, well not really. Because warm-blooded animals are always warm they can move at any time. An endotherm will nearly always outrun a similarly proportioned ectotherm because their muscles are just “good to go”. This also affects things like mating, conditions have to be right for cold-blooded animals to “get down” whereas warm-blooded animals can get jiggy whenever we want, but apparently not in the dairy aisle at Asda. That’s frowned upon.

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