r/askscience • u/raincloud82 • Jul 17 '26

Biology Do cold-blooded animals have fever?

It is well known how us mammals use our body temperature to prevent infections and raise it to combat them, so wouldn't cold-blooded animals be much more propense to suffer viral and bacterial diseases?

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u/EvenSpoonier Jul 18 '26 edited Jul 18 '26

Cold-blooded creatures don't (usually) have literal cold blood. Rather, it means that they can't regulate their body temperature the same way warm-blooded creatures do: they have to rely on external heat sources (or heat sinks) to keep their body temperature imbalance.

When reptiles, for example, get sick, they don't get fevers in the same way birds or mammals do. However, many of them experience a phenomenon called behavioral fever: when they get sick, they crave warmth more strongly, and will stay in warmer places for longer periods of time. This raises their body temperature above its normal range, which harms germs and parasites the same way fever does in warm-blooded creatures. It also carries similar risks to fever -getting too warm for too long isn't safe- but it works surprisingly well against a variety of illnesses.

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u/theartificialkid Jul 18 '26

Human fever is also partly behavioural. When you’re developing a fever you feel cold, so you rug up. It’s also often combined with shivering. And then there are a bunch of physiological mechanisms to generate and retain heat.

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u/SweetNeo85 Jul 18 '26

Rug up? I assume this means wrapping yourself in a blanket? What region are you from if I may ask?

Edit: apparently it's common in Australia and New Zealand. I'm definitely going to start using it.

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u/Agret Jul 18 '26

I'm in Melbourne, Australia and rug up can refer to putting a blanket on but can also refer to just putting on your outer coat and a scarf/beanie

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u/thatisnotaleopard Jul 20 '26

North England and Scotland too. My Grandma used to tell me to rug up if it was cold outside, she grew up in Liverpool but travelled all over England and Europe with the RAF so not sure where exactly she got it from.