Learned to dive in order to eat this bug.

For many small land animals, "scuba diving" is a very challenging project, not to mention "diving", just getting wet will become extremely embarrassing.

For example, for the Wang Xing people, the effect would be like this.

Hello, who are you? Picture: Sophie Gamand

What about cats? that's what happens.

Hello, can I help you? Picture: bored panda

So, what kind of situation is it for the bug?

Pest control warning! Pest control warning! Pest control warning!

A large number of bugs are infested, please evacuate the scene quickly!

At first glance, insects seem to be able to walk calmly on the surface of the water without getting wet. However, if you force them into the water, you will find that most insects will still get wet, trapped in the water and unable to break free, no better than your master Wang / Meow.

Of course, those bugs with their own paddling skills don't count. Picture: Pixabay

But! This kind of thing is a different story for Ephydra hians, a bug that lives on the banks of Lake Mono (Mono Lake).

Alkali flies from Mono Lake. Picture: Judy Gallagher / Flickr

Even Mark Twain, a great writer, lamented on the edge of Mono Lake 150 years ago: "you can put them in the water at will, no matter how long it takes, they don't care at all." they just feel proud of it. "the moment you release them in the water, they easily surface and come out drier than a newly released patent office document."

An alkali fly that floats leisurely to the surface after diving. Photo: Van, F. B.et al./Proceedings of the National Academy of Sciences (2017)

The Secret of Air diving suit

So, how on earth did these alkali flies become real-time "submarines" so that they could enter the water without getting wet?

If you look closely, the alkali fly will form an air bubble around its body and wings as it climbs into the water along the limestone, just like putting on a self-help "air diving suit" at the moment of entering the water. Most of the body will be wrapped in it, leaving only mouthparts for eating.

An alkali fly in an air diving suit. Photo: Van, F. B.et al./Proceedings of the National Academy of Sciences (2017)

After eating and drinking enough at the bottom of the water, it will release its claws from the limestone and let itself float. As soon as it reaches the surface, the "diving suit" automatically breaks and the alkali fly flies out of the water.

The diving skills of alkali flies can not help but make people envy, and how this humble little guy got the "air diving suit" has always been a mystery.

Alkaline fly that is diving in Mono Lake. Photo: Van, F. B.et al./Proceedings of the National Academy of Sciences (2017)

To solve the mystery, Professor Michael Dickinson of the California Institute of Technology led a team to follow in Mark Twain's footsteps and visited Mono Lake again, hoping to uncover the secret of the alkali fly air diving suit.

Mono Lake, beautiful but hidden opportunity. Picture: Vezoy / Wikipedia

Everything is a pot of lake water?

When they arrived at Mono Lake, they found that although the scenery was beautiful, the lake was alkaline, and only a few algae could survive, but the alkali fly seemed to live a carefree life here. ). After a survey, they decided to study the composition of the lake water and the body of the alkali fly.

Before the formal test begins, quantitative indicators and devices are needed to measure the "degree of wetness" of the subjects. It is conceivable that the more "wet" the subject is in the water, the more "muddy" it will be when it leaves the surface of the water, and the more work it will do.

To this end, Michael's team designed an ingenious device to fasten the insect to a stick and "press" it into the water, and then pull it out of the water (worm: too bad). In the process, optical sensors are used to measure the work required for insects to enter and leave the water, thus reflecting the degree of wetness of the subjects.

Device diagram and data examples for measuring the force required to enter and exit the water surface. Photo: Van, F. B.et al./Proceedings of the National Academy of Sciences (2017)

The Michael team first wanted to see what was so special about the Mono Lake water and whether there were any ingredients that kept the alkali flies from getting wet. However, they unexpectedly found that the lake water contained a large amount of Na2CO3, which was easier to "get wet" than other ordinary lakes. In the experiment, all kinds of flies similar to the length of alkali flies became so "wet" that it was difficult to escape after entering the water.

The wet degree of all kinds of flies, the smaller the Recovered Work, the "wetter" (alkali flies in the red box). Photo: Van, F. B.et al./Proceedings of the National Academy of Sciences (2017)

The kelp fly also capsized in the water. Photo: Van, F. B.et al./Proceedings of the National Academy of Sciences (2017)

It seems that the lake water can only be "unhelpful" and has no practical effect, and the core technology must be mastered by the alkali fly itself.

The more bristles, the more waterproof?

You can't see the difference with the naked eye, so you can zoom in and look at it.

So the researchers used a scanning electron microscope to take a high-definition picture of other flies, including alkali flies. They found that the surface of alkali flies was covered with the densest bristles than other flies.

Can "good hair volume" be the reason why alkali flies are not afraid to get wet?

Subsequent analysis found that flies with more bristles were less wet. However, this seems to be only one of the factors that make alkali flies "not wet". Although alkali flies have the highest setae density, they are only 15% more than kelp flies (Fucellia rufitibia), but their waterproof effect is much better than kelp flies.

The microstructure of the surface of various flies (the surface of the alkali fly in the red frame has dense bristles). Photo: Van, F. B.et al./Proceedings of the National Academy of Sciences (2017)

So, is there any other reason?

The team then became interested in the intimate "armor" with glossy surface of alkali fly bristles-they analyzed the chemical composition of this layer of armor using gas chromatography / mass spectrometry (GCMS) and found that most of them were 25 alkanes and 27 alkanes, which are different from other flies.

Is this the real answer that alkali flies don't get wet?

The eager research team soaked the alkali flies in hexane and washed all these long straight-chain alkanes before experimenting. Sure enough, the unarmored alkali flies lost their usual demeanour in the water of Mono Lake. After entering the water, they got wet like other flies.

The surface of alkali fly is mainly covered with straight-chain 25 alkane and 27 alkane. Photo: Van, F. B.et al./Proceedings of the National Academy of Sciences (2017)

Thanks to alkane armor!

Why long straight-chain alkanes "armor" can help alkali flies waterproof?

In fact, there are two main states when the liquid comes into contact with the rough surface: the first state is the Wenzel state: the surface gap is filled with liquid, which makes the whole solid surface very wet (similar to your master). The second state is the Cassie-Baxter state: the gap on the rough surface is filled with gas, similar to the "gas diving suit" of the alkali fly.

The surface of alkali fly is mainly covered with straight-chain 25 alkane and 27 alkane. Photo: Van, F. B.et al./Proceedings of the National Academy of Sciences (2017)

Which kind of state appears after solid-liquid contact depends on the charge interaction of the contact surface and other factors. For example, in the lake water with high concentration of sodium carbonate, the electrostatic attraction between the body surface of most insects and the lake water is strong, showing the first state, resulting in wet body; while the dense bristles and long straight-chain alkane armor on the surface of alkali flies effectively reduce the electrostatic attraction between the surface of alkali flies and lake water, thus showing the second state, giving alkali flies this layer of "air diving suit".

This cool way of diving is actually evolved by alkali flies to adapt to the extreme environment. If its mechanism is understood, it can also provide ideas for the development of new hydrophobic materials.

Nothing can stop the alkali fly from going into the water to find food!

The power of foodie is infinite! Picture: Floris van Breugel / NPL

Research tidbits

During the investigation of Mono Lake, the researchers stumbled upon a strange phenomenon-as long as they stood close to the edge of the lake, some alkali flies on the nearby lake lost their ability to "not wet" and were trapped after entering the water.

At first, they also wondered whether the alkali flies were afraid of people being scared. It was not until they saw the effect of hexane baths on alkali flies that they thought it might have been caused by their own oil-containing sunscreen.

Because of the hot weather, sunscreen drips into nearby lakes with sweat, bringing some oil into the lake and dissolving straight-chain alkanes from alkali flies, eventually causing them to get wet.

Alkali flies show innocence. Picture: Floris van Breugel / NPL

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