Dr. Floris van Breugel uncovers the secret of how Mono Lake’s alkali flies scuba dive while staying dry
Research completed this summer at Mono Lake and published this Fall in the Proceedings of the National Academy of Sciences has the potential to offer engineers new insight into the development of hydrophobic materials.
Dr. Floris van Breugel, a post-doctoral researcher at the University of Washington, discovered this summer just how Mono Lake’s characteristic alkali flies scuba dive under the lake’s surface by creating a bubble of air that surrounds their bodies and allows them to remain submerged for up to 15 minutes at a time.
Van Breugel has a background in engineering and studies biomechanics, or the way that animals coordinate their limbs to accomplish tasks such as decelerating mid-flight to land on a small surface. He is particularly interested in how flies manage to make complex decisions and perform extraordinary physical tasks to obtain food despite their miniscule brains. In his studies, van Breugel found that Mono Lake’s alkali flies exerted a force 18 times their body weight to plunge their bodies into the lake. He set out last year to figure out how they do this.
Van Breugel compared the performance of other alkali flies with Mono Lake’s flies in similar environments (similar species exist at Utah’s Great Salt Lake), and found that the flies at Mono Lake were 36 percent hairier than their relatives. Van Breugel also discovered that their bodies are coated in the same water-repelling hydrocarbon found in beeswax.
Mono Lake’s water is rich in sodium carbonate, which van Breugel described as “a very strong version of baking soda.” Van Breugel discovered this summer that the presence of sodium carbonate in water makes it stickier. It clings to foreign surfaces more readily than fresh water does, and it is better at permeating waterproof materials as a result.
The presence of sodium carbonate in the water at Mono Lake creates a slightly negative charge at the lake’s surface. When an object like a fly or a piece of clothing comes into contact with that surface, positively charged molecules on the fly are attracted to negatively charged molecules in the water. “This pulls the lake water close to the surface of the fly,” said van Breugel.
Mono Lake’s alkali flies, unlike fruit flies, have a waxy, paraffin-like coat that repels the negatively charged molecules at the lake’s surface. As they submerge themselves (head first), the waxy cuticle that surrounds them repels the water, creating a bubble of air that encases the fly as it moves into the depths of the lake. In order to submerge themselves, the flies have to muster more force than is generated by their waxy cuticle’s repulsion of the lake water.
This adaptation to form an air bubble allows the flies to lay their eggs and feed on algae below the surface of Mono Lake, out of reach of predatory migrating seabirds. The lake is fishless, and van Breugel said the flies are an essential part of the global food chain. “All of the nearly two million migratory birds that stay at Mono Lake for a week or so during the year feed on the alkali fly,” said van Breugel. “As you can see, these flies are a very important part of the global ecosystem.”