“Water beetles have been breathing underwater since before the dinosaurs existed,” said Crystal Maier, an entomologist at The Field Museum in Chicago. “It has evolved at least 10 times across the insect tree of life.”

How do they do it? Surface tension — that cohesive force between liquid molecules, attracting them to each other over molecules that they don’t share as many properties with, like the molecules in the air. Those liquid molecules create a film, and for a tiny animal like a beetle, that film behaves differently than it does for humans or other large animals. KQED’s Deep Look explains more:

If you’re a bug the size of a paperclip, in other words, surface tension makes a difference. Harnessing it, some aquatic beetles carry the oxygen they need underwater in the form of a temporary bubble, sort of like a natural scuba tank. Others encase themselves in a layer of air and draw oxygen from it their whole lives.

“It’s a pretty successful group of insects. They’re on every continent, except Antarctica,” said Cheryl Barr, collection manger emeritus at the Essig Museum of Entomology at UC Berkeley.

A related must-read: How Insects Breathe by Aatish Bhatia and Robert Krulwich at Noticing.co, complete with animated illustrations by Eleanor Lutz.

Watch more surface tension videos, including SciFri’s Stroke Of The Water Strider and PhysicsGirl’s seven surface tension experiments you can try.

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