hi dr ferox! speculative biology question for you: is it possible for an alien species to exist that has an exoskeleton but is warm-blooded? (i’m thinking around human-size, perhaps a little smaller) i couldn’t find any examples on earth (honeybees can cool themselves actively or huddle for warmth but that’s as close as earth-creatures get) but i’m curious as to whether it’s even theoretically possible for a world-building project i’m working on involving an insectoid/humanoid species.

drferox:

It’s certainly theoretically possible to have a species which is endothermic and has an exoskeleton. You can find species of fish with scales that are endothermic, an as body mass increases the more difficulty that species will have cooling off.

Also note pangolins which have kertin scales that could look an awful lot like an exoskeleton, and they are endotherms too.

The question I would be asking is whether this species only has an exoskeleton, or whether it also has an endoskeleton. Because when you scale up, I think beyond a meter or so from memory, an exoskeleton may not be enough support on its own. You will also need vertebrate-style lungs and a circulatory system rather than an insect-like haemolymph as passive diffusion will not remain adequate as the creatures get larger, even in a high oxygen environment.

Seahorses are ectothermic and are technically vertebrates, but they may be worth looking into, as their skeletal structure also functions as something almost like an exoskeleton. They feel armored to the touch, their skeleton protects them extremely well. 

Also, arthropleura was a prehistoric millipede-like creature that could get over six feet long. Still an arthropod, essentially just a giant bug, but that size is possible. They lived in a much more oxygen-rich environment, though. 

So, as mentioned above, you’re probably going to need to give them some form of lungs. If you want to stick to a buglike idea, you could have them breathe through slits in their sides that lead to lungs.