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Written by | Seven Jun
Have you ever wondered why flies can wander the moon at will on smooth vertical surfaces, such as glass and lead heads? If fly legs can "suck" on the surface of an object, then why do they fly away easily when we reach out to hit it, seemingly completely ignoring this "stickiness"?
This question has only been reliably answered in the last 30 years. After reading this answer, although the small fist you swing at the flies will clench more tightly, you have to sigh at the skill of this king explosion they have.
Humans have always been interested in the fact that insects, especially flies, can fly over the wall, and the earliest academic research dates back to the 17th century.
No one would suspect that flies can "climb the tree" skill points on their feet. Researchers have also proposed various explanations for the skills of the fly's feet and feet, such as the particularly good grip of the fly's feet and feet, and the static electricity on the feet.
Small fruit flies can climb the vertical glass test tube wall at will. Image source: doi.org/10.1038/s42003-020-0995-0
In 1862, the British entomologist Tuffen West pointed out that the problem of fly feet and feet has been studied repeatedly, and many people think that this problem has been perfectly answered, and there is no longer any question worth exploring.
But things reversed in the 1980s. Past theories were refuted in 1983 by researcher Nigel E. Stork at the British Museum of Natural History. Stork found that the fly's "foot hair" and "foot sweat" were the key.
Yes, flies not only have foot hair, but also sweat on their feet. Please watch the beautiful and thick foot hair of the fly -
Hairy feet of flies under an electron microscope. Image credit: Stanislav Gorb
We must look at the problem comprehensively and dynamically --
As you can see in the picture, in fact, insects mainly rely on two kinds of "hairy hands and feet" body structure to achieve climbing, the first is the tarsal node of the foot (similar to human hands and feet), and the second is the hair on the foot (similar to the sweat hair on the hands and feet).
A pair of claw pads of moflies (round as 5). Image source: wikimedia
Specifically, the hairy feet of insects such as diptera, which have evolved to be new, resemble suction cups, a biological device called a pulvilli. They also have "foot hairs", or bristles, on their claw pads.
This foot hair is different from our foot hair, the fly's foot hair is stuck to your shovel, it looks like a smaller claw pad, and each foot hair of the fly is developed from an epidermal cell, which is very delicate.
Shovel-shaped foot hairs (bristles, light blue) are one of the key factors in the adsorption of fruit flies on vertical surfaces. Image credit: Hokkaido University of Education
Each claw pad is covered with about 30 matryoshka hairs, and the main purpose of growing so many foot hairs is to increase the contact area and thus increase the suction. But without the sweat of the feet, the fly's wall climbing skills would not be so strong.
Stork points out that the capillary phenomenon produced by the sweat of the fly's feet and the van der Waals force (the attraction of molecules and atoms when they are close together) can provide a huge suction force. If the flies are allowed to walk on the silicone for 15-30 minutes and let the silicone absorb the sweat of their feet, then they will not be able to walk on the smooth surface.
Image source: wikimedia
Therefore, when the fly walks, it will leave a trail of foot sweat and footprints. In 2015, researchers at the Universities of Osnabrück and Kiel in Germany found that fruit flies leave clear droplets of foot sweat where they walk, exactly the same shape as their foot hairs.
However, people do not know where the sweat of the flies' feet comes from. This question was not answered until 1998.
That year, Stanislav N. Gorb, a researcher at the Max Planck Institute in Germany, and colleagues used electron microscopy to discover the secret of fly hair. It turns out that this foot sweat does not flow from the claw pad, but from the tip of the foot hair (the end of the bristle). He speculated that when the fly's feet pressed against the surface, the foot sweat would automatically squeeze out like a hand sanitizer, and when the fly took off, the foot sweat would be partially recycled.
Interestingly, he found that when flies are walking, their foot hairs are relatively stationary on the surface of the object, and there is no sliding friction. That is, when the fly walks, it moves like a foot on a suction cup.
Gorb later discovered in 2006 that when it comes to eliminating stickiness, flies have three sets of movements: pushing, twisting, and pulling, just like humans pulling. Among them, the action of pulling a pull is the most labor-saving.
At this point, the problem of easy evasion of the fly's cornices has been answered: the fly's foot hair and foot sweat provide a strong adsorption parallel to the surface of the object. But because the capillary action and van der Waals force produced by foot hair and foot sweat need to be close to the surface of the object to work, the fly only needs to gently raise its legs, these two forces will automatically dissipate, and the stickiness will disappear. It turns out that the space dance steps of the flies' feet and feet come from this way.
If you still don't understand the toughness of the fly's feet, take a look at the effect of humans restoring the feet of the flies.
See, the fly's feet are used like this: if you pull along the surface of the object, it is difficult to pull apart; but if you make the force perpendicular to the surface of the object, a gentle lift can release it -
Image source: See watermark
This is the same type of foot hair made by the National Institute of Materials Research (NIMS) in 2020 by studying the formation process of Fruit Fly foot hairs.
The reason why they were able to create the same foot hair of the "hand rubbing boy" was because they carefully observed the development of the feet of the baby of drosophila melanogaster.
The feet of the drosophila (bristles) and its development process. Image source: See watermark
In fact, this extraordinary foot hair is produced in the process of metamorphosis of the baby fruit fly, and the formation of the foot hair takes only two steps: the epidermal cells to become the foot hair are continuously elongated, and then the protein (actin) accumulates on the top of the elongated cell to form a shovel. In this way, a cell develops into a foot hair.
Inspired by the development of fruit flies, they used low-grade materials to create a powerful tool that was as sticky as the feet of fruit flies: the foot hair was elongated nylon silk, the foot sweat was calcium alginate, and the two nylon wires were soaked in calcium alginate solution, pulled out, and the whole process could be conveniently carried out at room temperature.
The process of making the same foot hair of the fly is very simple, soaking two nylon wires in a calcium alginate solution and pulling them out. Image source: See watermark
According to their calculations, a shovel with a cross-sectional area of 9 square centimeters can lift a human weighing 60 kilograms, but as long as it is pulled in the right direction, the shovel can fall off with one key and can be used repeatedly.
To be honest, many of the sticky materials made by humans, such as stationery glue, are disposable, and can no longer be used after scraping off. However, the feet of flies are different, although their stickiness is very strong, they can repeatedly adhere to various surfaces and can easily fly away. If this bionic tool can achieve large-scale production, humans may be able to reduce a lot of garbage and pollution.
Flies: I have big eyes, furry and sticky, claws are more than the shape of the heart ♥️, "honey juice" is good to pick up.
Cover source: pixabay
Resources:
https://docs.qq.com/doc/DVGNGc3pQcW5DZnNT
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