The next time a bird craps on your car, say thank you. A little poop is a small price to pay to keep from having to fight off insects with wingspans of twenty-eight inches. Find out the evolutionary twists that kept people from having houseflies the size of kittens.


Humans need oxygen to survive. This is generally not such a hardship, although it makes undersea and space travel harder than they need to be. It would be a little harder, though, if the trade-off for being in an oxygenated world was having to bat away the kind of insects that were last seen in the King Kong remake. Before that, they were seen in the late Carboniferous and early Permian eras, roughly 300 million years ago. These flying insects had wingspans between twenty-two and thirty inches wide. Some ate smaller bugs. Some ripped or sucked parts out of larger creatures. None of them were the type of things that you would want to have to shoo away from your potato salad.

Traditionally, as oxygen levels went up, insects got bigger. Insects don't have lungs that can be pumped full of air. They have tiny breathing tubes scattered around their body, and rely on oxygen that they get through these thin straws. As oxygen levels go up, they can fuel bigger and bigger bodies, and insects get huge. Or at least they did.


The trend towards giant insects got stopped about 150 million years ago. Although oxygen levels in the atmosphere went up, insects got smaller. This is because birds had appeared on the scene. Although far more people recoil from an insect than from a sparrow, the latter is higher up the food chain.

Birds are sturdy, fast, agile, and deadly. And large insects were their easiest prey. Big flying bugs just didn't have the maneuverability they needed to outfly their hunters. They could breathe well enough, but they wouldn't be breathing for long. Since then, birds have been keeping the giant horrifying bug population under control for us. And they've been doing it while being far cuter than the insects. Hopefully, the next evolutionary leap forward will give us something that looks like a baby otter and preys only on spiders, and the world will, once again, be made a better place.

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Via PNAS.