Where did all the giant bugs go? You've probably seen paleoartists' depictions of dragonflies the size of kites,

ants the size of rats, millipedes, the length of Christmas trees, and so on and so forth,

and then you look around at the tiny creatures in the room with you, and you wonder,

what happened to the big bucks?

Bugs isn't the most technical term. It refers to insects, arregnids, and myriopods,

the last term meaning the highly segmented creatures we call millipedes and centipedes,

we'll talk more about today. Now, while there was a time when bugs could get absolutely huge,

as of late, nature seems to have disposed of the larger weight divisions for these animals.

Why? Well, there are a few ideas floating around this space, but I'll tell you the one I like.

I'm reading it from the insect physiologist John Harrison, although I think the idea predates him,

and it has to do with oxygen. Basically, bugs breathe passively through a bunch of tiny tubes

all over their body, rather than actively through lungs. Now, we know from observing animals in nature

that bigger bugs generally need more of these tiny tubes proportionately, implying that something

about them makes each tube increasingly inefficient at scale.

Now, a body needs space for more than just breathing tubes, and the theory goes that big bugs

are disadvantaged, selectively, by the need to make space for so many breathing apparatuses.

We also know that in the time period when bugs were biggest, Earth's atmosphere was about 35% oxygen, rather than the 21% we live with today.

And that's a massive difference. So it's certainly plausible that the reason bugs were once bigger than they are now is because

the higher oxygen content could support larger tube-breathing creatures.

Today, in our comparatively low-oxygen environment, animals without lungs generally struggle to

pack on size.

Every big bug today is only really big for a bug.

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