[Anonymouse]

Originally Posted by patrickp

I thought all insects respire through spiracles in their abdomens (and maybe thoraxes)?

This is the reason insects can never get very big.

They do indeed breathe via spiracles, but that's not the reason for the size limitation, about 12". Their breathing process is a form of diffusion, and if the insect were any bigger it simply wouldn't work. Mind you, even a stick insect is a bit worrisome when it's 12" long.

And as for those dragonflies millions of years ago - if birds had been around then, those monsters could've picked 'em off! Even today's dragonflies are intimidating - you know, those about 4 or 5 inches long? Imagine one of those a foot long! Scary or what?

Did you know dragonflies can fly backwards?