Why Giant Bugs Once Roamed the Earth

Imagine a dragonfly the size of a seagull! You would have seen them 300 million years ago, as well as other B-movie sized insects. Why did they grow so large back then? A new theory says it's because of oxygen, which insects absorb through their surface area. Wilco Verberk of Plymouth University found that insect larvae are very sensitive to oxygen levels compared to adult insects -and there was a lot more oxygen present in the Carboniferous period.
It's likely the larvae of many ancient insects also passively absorbed oxygen from water and were not able to regulate their oxygen intake very well—a big danger when oxygen levels were so high.

One way to decrease the risk of oxygen toxicity would have been to grow bigger, since large larvae would absorb lower percentages of the gas, relative to their body sizes, than small larvae.

"If you grow larger, your surface area decreases relative to your volume," Verberk explained.

Read more about the study at National geographic News. Link

(Image credit: Ned M. Seidler, National Geographic)

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Was just going to say what Jessss just said. I heard about this theory, high atmospheric oxygen levels and large insect size, quite some time ago...
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