If you've ever visited California's Mono Lake, the shallow lake that's three times saltier than the ocean, you may have seen flies crawling into the lake only to emerge from it perfectly dry — without needing to shake off, even a little bit.
So just how do these flies stay so dry after their salty dip?
According to a study published in the Proceedings of the National Academy of Sciences, it has to do with hair, wax and bubbles.
An inhospitable lake
Lake Mono is beautiful but it's a deadly body of water for many organisms. (Photo: Ron Reiring/flickr)
Mono Lake, which is about 13 miles outside Yosemite National Park, isn't for the faint of heart. In addition to its salty contents, the lake is filled with borax and sodium carbonate, which is basically laundry detergent. The combination of these ingredients gives Mono Lake a slippery and sudsy feel. It also means the lake is deadly for many organisms, including insects. After all, insects get wet and weighed down in a swimming pool, so Mono Lake should be a death sentence for its resident alkali flies (Ephydra hians).
But the opposite is true. In addition to being a hot spot for algae, bacteria, brine shrimp and various water fowl, the alkali fly loves breeding and feeding along the shores of this difficult environment. While the birds like to feast on the plentiful flies, the flies eat the algae, both as larvae and as adults. This is a good deal for the flies since there aren't any predators for them to avoid while they're underwater. Except, you know, that they're underwater and shouldn't be able to get to the surface.
When the alkali flies dive into the lake, an air bubble forms around them, supplying them with protection and oxygen. The flies are able to skitter along the lake's bed for about 15 minutes, reaching depths of 25 feet. Once there, the flies can feast as much as they want and even lay their eggs. After they're done, they pop out of the water, well-fed and completely dry.
Such a feat would be a death sentence for any other insect. They would never be able to survive under the water, let alone escape from it.
The best waterproofing ever
To figure out how the alkali flies were able to dive and escape, researchers at Caltech glued individual flies to tungsten rods and dunked the flies into water, using a motor to raise and lower them into the tank. The researchers measured the amount of force the flies exerted when entering and exiting the water. They found that the flies use force up to 18 times their body weight to enter the water, gripping the surface with their feet. When they're leaving, the flies are essentially pushed out of the water.
Figuring out that the flies were pretty strong and determined helped the researchers, but they also wanted to know how the lake itself influenced this behavior. To that end, they dipped more flies into more tanks, this time mixing up the solutions' pH and other compounds. The sodium carbonate turned out to be the chemical that would drown most other insects by layering the flies' bodies (which carry a positive charge) with negatively charged carbonate ions, essentially soaking all flies. Unless they were alkali flies.
All flies have hairs on their bodies that, with a waxy coating, help them be somewhat water repellent. Alkali flies differ from their cousins and even closer relatives in that they are exceptionally hairy and waxy. The combination of these two enhanced traits make alkali flies superhydrophobic. The flies part the water around them, knocking away those pesky negatively charged carbonate ions that would drown lesser flies and creating that cool air bubble. That air bubble, by the way, doesn't surround the flies' eyes, so they're able to see the water clearly, without any distortion.
The wax is likely the key to the whole trick. When researchers washed away the wax, the alkali flies were unable to stay dry in Mono Lake's waters. Knowing the compounds that the flies use to be so hydrophobic could be a boon to making other things water-resistant, including electronics and roads.