This little guy is an alkali fly. Unlike most winged insects, it has the very unusual habit of laying eggs and foraging beneath the surface of the salt-filled Mono Lake of Yosemite National Park.
Mark Twain even wrote about this peculiar behavior in his 1872 memoir Roughing it, playfully noting: “You can hold them underwater as long as you please – they do not mind it – they are only proud of it. When you let them go, they pop up to the surface as dry as a patent office report.”
Biologists from Caltech have recently been re-studying these flies and discovered the unique adaptations that allow them to dive in the quite inhospitable environment of Mono Lake. Their study is published in the journal Proceedings of the National Academy of Sciences.
They discovered that the alkali fly makes a mini-submarine, creating a protective bubble of air around its body. Above water, alkali flies are fairly innocuous-looking hairy flies. As you can see in the photograph above, when submerged in water they are encased in a silky smooth air bubble.
The flies do this by covering themselves with a specialized wax that is super-effective at repelling the carbonate-rich water. They are 36 percent hairier than other species of fly, making it easier for air to get caught in a bubble around them. On top of that, they have large hooked feet that allow them to grip on to underwater rocks.
It’s important to remember that Mono Lake is also no ordinary lake. It’s three times saltier than the ocean, packed with sodium carbonate and borax, and has an extremely high pH. As such, no fish can survive there. The wax of the diving fly is especially well-equipped to deal with this slippery, super-alkaline water. Although a few insects use this method of “scuba diving”, no other flies could take a dunk in Mono Lake and live to tell the tale.
"It is such an incredibly weird thing for a fly to deliberately crawl underwater," study author Michael Dickinson pointed out, though he explained that the flies haven't evolved a new way of remaining dry, but instead just amped it up to a level unseen in most other insects.
"It's just a killer gig. There's nothing underwater to eat you and you have all the food you want. You've just got to dive in perhaps the most difficult water in which to stay dry on the planet," he shrugged.
Luckily for them, they figured it out. "It's amazing how the evolution of such small-scale physical and chemical changes can allow an animal to occupy an entirely new ecological niche."