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These Super-Hairy Flies Can 'Breathe' Underwater

An "external lung" allows these flies to flourish where almost no other creature can: California's Mono Lake.

Photos and Video: Floris van Breugel

We’re used to seeing flies all the time, probably throwing up on your plate of food or hovering around a garbage can, but how often do we see flies do something awe-inspiring like breathe underwater?

Mono Lake, California, is home to the bizarre and hairy alkali fly (Ephydra hians). Researchers have now found that these “diving” flies are able to withstand the lake’s highly alkaline waters, crawling into it to feed and lay eggs. The hair on their body helps to create a bubble of air around them, which acts as an external lung.

The research was conducted by Floris van Breugel, a National Geographic Society Committee for Exploration and Research grantee and postdoctoral candidate at the University of Washington. The National Geographic Society funded van Breugel to study the flies that inhabit Mono Lake. It’s the same species of flies, he says, that Mark Twain wrote about 150 years ago in his book Roughing It—“because they’re really just that entertaining to watch,” says van Breugel. (Watch flies eat a donut.)

The sheer number of flies that inhabit the lake’s shores is impressive. They are so densely packed that within an area about the size of a postcard, there could be over 2,000 flies. van Breugel estimates that in the height of the summer that could mean around 100 million alkali flies buzzing around Mono Lake.

Things really start to get interesting, though, when you take a closer look. “You can start to see them actually crawling underwater in little air bubbles,” he says.

Solving a Mystery

van Breugel and his team set out with the goal of understanding exactly how the alkali flies of Mono Lake are able to crawl into the water, which is three times saltier and much more alkaline than the ocean, without getting wet. The only known creatures that inhabit it year-round are photosynthetic algae and a species of tiny shrimp. The study was published on November 20 by Proceedings of the National Academy of Sciences.

The scientists built a sensor capable of measuring tiny forces and then dunked the alkali flies into a series of different solutions. They were surprised to find that more highly concentrated lake water made it easier for the flies to drown, as opposed to solutions with less salt and mineral content. The culprit turned out to be sodium carbonate, or washing soda. Not only is it an effective cleaning solution, but it has also historically been used to preprocess mummies in ancient Egypt.

The sodium carbonate makes it harder for alkali flies to stay dry, as water is more easily pulled into the spaces between their hairs. The hairy alkali flies’ evolutionary response has been to produce more hair—36% more than the other flies that the team tested it against, to be exact. The flies’ hairs are also coated in a special wax, which further helps to keep them dry. It’s the same concept as waxing your car, or your shoes, to make them more weather-repellent.

The Bigger Picture

“Because of these tiny adaptations, the alkali flies are able to occupy a niche that very few other animals can tolerate,” says van Breugel.

This hairy adaptation has led to significant global ecological effects, the scientist notes, as Mono Lake serves as a stopover point for over 2 million migrating birds each year. This includes 85 percent of all California gulls, which nest on islands in Mono Lake.

van Breugel’s findings are one example of how one small evolutionary change (even those the size of flies’ hairs) can have a big impact on an ecosystem and beyond.