Dragonflies the size of hawks once ruled the prehistoric sky

Around 300 million years ago, the sky belonged to Meganisoptera—giant dragonflies with wingspans reaching nearly two and a half feet. These werent just large bugs; they were apex predators the size of modern birds of prey, capable of snatching small amphibians right out of the mud.

This nightmare-fuel biology was possible because Earth’s atmosphere was roughly 35% oxygen, compared to just 21% today. Insects don’t have lungs; they breathe through tiny tubes called tracheae that rely on passive diffusion. In a high-oxygen world, that gas could penetrate much deeper into their tissues, fueling massive bodies that would literally suffocate in our current air.

As oxygen levels eventually dropped, these giants couldn't keep up with their own metabolic demands and shrank to the sizes we see today. It serves as a reminder that the very chemistry of the air dictates the physical limits of every living thing on the planet.