Flies in a Californian lake have abandoned the air for the water.
The “diving flies” of Lake Mono can crawl underwater without even getting wet.
Now scientists have discovered how these insects are able to survive underwater and remain dry.
The flies are incredibly repellent to water; so repellent that a protective bubble of air forms around their bodies when they enter the water.
They also have clawed feet that they can use to anchor themselves to the bottom of the lake.
This strange behaviour was described by the novelist Mark Twain in his travel memoirs, but has never before been understood.
"You can hold them under water as long as you please – they do not mind it,” wrote Twain.
“They pop up to the surface as dry as a patent office report.”
Plunging underwater is “a death sentence” to most insects, said Professor Michael Dickinson, a fly researcher at the California Institute of Technology and one of the study’s co-authors.
Lake Mono in particular doesn’t seem like an attractive place to live. It’s highly alkaline and three times saltier than the ocean.
Despite this, its conditions have proved appealing to these unusual insects.
The hostile conditions mean that there aren’t any predators living in the lake that could eat the flies, but plenty of bacteria for them to feed on.
"It's just a killer gig. There's nothing underwater to eat you and you have all the food you want,” said Professor Dickinson.
The flies’ eyes are left uncovered by the bubble, allowing them to search for prey without any distortion.
The chemical composition of the lake should actually make it more difficult for insects to enter it, as negatively charged ions in the water are attracted to positive charges found on insect skin.
What Professor Dickinson and his collaborator Dr Floris van Breugel found was a particularly thick covering of hairs on the diving flies. This hair was coated with water-repellent wax that gave them their aquatic abilities.
The scientists are interested in the applications such a wax might have in materials science, but also in the neurobiology underlying a fly’s decision to live in a lake.
“It is such an incredibly weird thing for a fly to deliberately crawl underwater," said Professor Dickinson.
