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Lice don’t just thrive in the biomes of body hair and fur, they can also live in a place that seems like it should be bug-free: the oceans.

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If you go almost anywhere on Earth, you can find an insect. Seriously, there are ones living in Antartica's ice, others hanging out on lava flows in Hawaii. There is, however, one place that's pretty bug-free, the oceans. A few species live near the shore, and one can skate across the top of the water. But for reasons scientists don't really understand, insects have largely steered clear of the great blue sea.

Except we do know of one that does more than just splash around. The Elephant Seal Louse. It turns out a close cousin of the thing that plagues your hair in elementary school is also one of the hardiest creatures on Earth. These lice can ride elephant seals to depths of more than two kilometers. Down there, the lice need to deal with enormous pressure. 200 kilograms per square centimeter on their tiny bodies.

That exceeds what deep diving military submarines experience. And for a while, scientists weren't sure if the lice survived these dives or not. There are definitely living lice in elephant seal's coats, but those could have been picked up right after a seal came up from a dive. So to figure it out, researchers took lice from the flippers of seals in Argentina and brought them to a lab to put them through an epic ordeal.

They placed the lice in a bronze container and ramped up the pressure until it reached the equivalent of being under 2 kilometers of water. Then, they left it for 10 minutes. After releasing the critters, they closely examined them to see if any survived, and nearly all of them did! One louse was so hardy that it even survived a kind of lucky accident.

While setting up the equipment, a technician accidentally exposed a louse to the pressure equivalent of more than 4.5 kilometers of water, far deeper than any marine mammal has ever been seen diving. But hey, it made it! Biologists aren't sure what adaptations make these lice different from other insects, but they've got a few ideas.

All the species of lice that live on marine mammals are covered in tiny, hard scales, so that could provide a sort of armor to protect them from high pressures. Or it might just be that a louse isn't very compressible in the first place. If they're able to immobilize their digestive and breathing system somehow, there's not much else that can be crushed. And as far as how the lice breathe during those dives, there are some ideas there too.

Like maybe they can store a layer of air underneath their scales, or even get air from the water. Or they might just be really good at "holding their breath", in a sense, by slowing their metabolism down to use as little oxygen as possible. One way to find out would be to repeat the pressure experiment, but monitor how much oxygen from the water the lice consume.

Except that requires collecting loads of lice, which for some reason nobody's done yet. Still, if we can figure this out, the answers to questions like that might have implications far beyond elephant seal lice. After all, these are the only insects who can dive so deep into the ocean, so learning more about what makes them different could help scientists figure out why others won't or can't take the plunge.It's also just nice to know that way deep down there, elephant seals might be just as itchy as we are.

Earlier, we mentioned a scientist who exposed a louse to way too much pressure, and we feel for them. Mistakes happen all the time. In fact, that's a big theme in Brilliant's new Math History course. It follows the lives and research of some of history's biggest mathematicians, all of whom made some major mistakes.

The course covers everything from prime numbers to ancient patterns, and like all of Brilliant's courses, it's designed to be hands-on and easy to follow. So if you want to check it out, you can go to, and the first 200 people to sign up there will get 20 percent off their annual premium subscription.