2017-11-22 11:10:04
Trilobites: The Scuba Diving Flies of California’s Mono Lake

11:10, November 22 57 0

Most people visit Mono Lake in California for the Dr. Seuss-esque towers called tufas. But to experience the truly bizarre, look for the scuba diving alkali flies.

A hundred years ago, the peculiar behavior of these insects charmed Mark Twain, who wrote in his travel memoir, “Roughing It,” that you could hold the flies underwater and they’d pop back up, alive and “dry as a patent office report.”

For most insects, water is a death trap. “Flies just do not crawl under water. It’s just a stupid thing to do,” said Michael Dickinson, who studies flies at the California Institute of Technology.

In water, they inevitably become fish bait or can’t escape or emerge too wet to function. But in Mono Lake’s salty waters, the fly species Ephydra hians is an exception.

Determined to find out how the flies accomplished this feat, Dr. Dickinson teamed up with Floris van Breugel, who now studies fly and mosquito behavior at the University of Washington, Seattle. They published their discoveries in the Proceedings of the National Academy of Sciences on Monday.

The fly’s secret to staying dry is an air bubble — a tight, flexible, silvery sheath that the fly dons like a “a superhero costume,” said Dr. Dickinson.

Its body — hairier and waxier than that of other flies and insects — repels water, forming a bubble around itself as it dives. In a way, the fly carries the dry sky down with it.

The bubble does not cover its red eyes, allowing the fly an undistorted view through the water. It walks along the tufa without becoming too buoyant by clinging on with elongated claws.

These adaptations are particularly impressive in Mono Lake, where the water is also extraordinary.

The hypersaline conditions make it inhospitable to fish, but very hospitable to brine shrimp, algae and bacteria. Underwater, the alkali flies feast on algae and lay eggs free from competition and predators.

But the flies first had to adapt to the lake’s chemistry. Containing borax and sodium carbonate, the water is better for washing laundry than swimming or inhabiting. It’s slippery, greasy, thick and “particularly wet,” said Dr. Dickinson.

The sodium carbonate carries an electric charge to the water’s surface. There it seeks an opposing charge — perhaps your body, if you happen to be swimming there. The water sticks to the spaces between hairs better than seawater or freshwater would.

That’s a problem for other insects, the researchers found. Many have waxy or greasy hairs fine for repelling dew or rain, but inadequate for Mono Lake’s sticky water.

With high speed cameras and a few calculations, Dr. Dickinson and his colleagues found it was their extra hair and body wax that allowed alkali flies to repel the water and form their bubbles.

“Mono Lake flies are like hipsters in Brooklyn,” said Dr. Dickinson. “They’re especially hairy, and they slather up with really good skin lotion.”

On the surface, the fly pushes its head under water, then its feet. Air trapped around the body closes into a bubble as the insect submerges, and within milliseconds, it’s walking underwater. It can stay under about 15 minutes.

When the bubble rises and touches the surface, it fuses with the air above the lake, creating a dimple that flattens out, slingshotting the fly upward and depositing it on the surface.

If you head to Mono Lake, especially in the summer, you can see the flies yourself. From afar, you’ll notice a writhing brown carpet of them at the shore.

If you disturb them, the flies will escape in an undulating wave. Head off-trail toward the tufa towers emerging from the water, and look underwater near the shore. There, flies use calcium carbonate rubble as a boat ramp to enter the water.

Just when you’re ready to give up, you’ll notice one, two, then hundreds of flies doing their own version of scuba diving. Enjoy.