After Hundreds of Years, We’ve Finally Figured Out How These Flies Can Swim Underwater

Alkali flies have been a fixture of Mono Lake, California for hundreds of years, but scientists only recently unravelled the secret of their aquatic abilities.

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Jul 17 2018, 2:00pm

Image: Screengrab/YouTube

There are aquatic insects that can live on, or partially in, water. But diving under the surface for extended periods of time is a rare skill. One creature with this strange ability, the alkali flies found in Mono Lake, California, only recently had the source of its diving skills revealed thanks to researchers at the California Institute of Technology.

The secret to their swimming success? Hairy, greasy bodies.

“I had seen [the flies before], but it's not really until you start looking for it that you see that they're in fact kind of all over the place, crawling underwater inside these little bubbles,” Floris Van Breugel, a biology research associate at the University of Washington and lead author of the 2017 study, told Motherboard’s podcast Science Solved It.

Tiny alkali flies are typically 6 millimeters long—about half the width of your pinkie. They live in huge swarms around Mono Lake, an ancient, highly alkaline terminal lake east of Yosemite National Park. For hundreds of years, these flies have been observed diving into the lake, creating a tight air bubble around their bodies, and swimming through the water, where they lay their eggs and feed on algae.

“More than two hundred years ago at least, the native Americans that lived in that area, the Kucadikadi tribe, used to harvest the pupae of these flies, as an important food source,” Van Breugel told me. “Their name Kucadikadi actually means ‘fly eaters,’ and they even traded those [pupae] across the Sierra Nevada so they were a pretty desirable food source, even for other tribes.”

Even Mark Twain was charmed by the strange bugs when he visited Mono Lake in the 1860s. Later, in his travel book Roughin’ It, Twain recounted his experience seeing the flies for the first time.

“You can hold them underwater as long as you please—they do not mind it—they are only proud of it,” Twain wrote. “When you let them go, they pop up to the surface as dry as a patent office report.”

But very little research had been done on the flies until recently when Van Breugel and his coauthor, CalTech bioengineering professor Michael Dickenson, decided to take a look. To crack the case, they gathered samples of the flies and brought them back to the lab, where they glued them to the end of tiny tungsten rods, and dunked them into various kinds of water: pure H2O, acidic water, and alkaline water like the kind in Mono Lake. Using a microsensor, they were able to measure the force required for the flies to break the surface of the water and form their “scuba suit” air bubbles.

They found that highly alkaline water actually made it even more difficult for the bubble to form, but the flies are covered in enough waxy, hydrocarbon-coated hairs that allow them to form their air bubble in even extreme environments. As the flies breach the surface of the water, the tiny pockets of air between the hairs are forced together by the pressure and form the bubble.

“You can kind of think of it as a dry suit, or a superhero costume that the flies wear as they crawl into the water,” Floris said.

Understanding the flies is helpful for completing a picture of the Mono Lake ecosystem, which is a vital pitstop for millions of migratory birds.

“From the birds perspective, they are these super essential resources during their migration and breeding,” Dickenson told Science Solved It. “It's just one of these places where you can see those connections very clearly. And I find that very rewarding, because the world's a complicated place.”

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