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There are brushed jumping spiders, they can maintain a certain posture in the air, stabilize their bodies before landing, and land smoothly.
Text/Guan Zhi
Manga/Eun Yu Zhen
My field of study, called comparative biomechanics, specializes in the physics behind non-human biological motion, often working with experts in different fields. Due to differences in professional backgrounds, the communication process creates many divergences, part of which comes from the definition of rigor.
There's a story that on a British train, three scientists, biologists, physicists and mathematicians, were sitting together on a british train who were about to attend a science gathering. At this time the train passed through a grassland, and outside the window there was a black sheep grazing. The biologist spoke first, and he excitedly said, "It turns out that the British sheep are black!" The physicist frowned and said, "You biologists are really not rigorous, you can only say that the British sheep, this one is only black." And then the mathematicians also frowned and said, "You physicists are really not rigorous, you can only say that the British sheep, this one, this side is black."
This joke is a vivid presentation of the scenes I will encounter in the course of my research, and since I have a biological background, I am usually the one who makes jokes. A large part of the study of biology in the aspect of animal behavior is based on observation. In describing behavior, biologists often add subjective speculation that is sometimes not entirely correct. An interesting example is why a jumping spider pulls a silk thread at the beginning of the jump when jumping?
The arachnid family is a family of spiders, and most species in this taxon do not form webs, but rely on jumping to catch prey. Probably because their jumping to flies has the tendency of a tiger to pounce on a rabbit, they are also called fly tigers. Biologists have found that although the jumping spider is less likely to form webs, it still produces spider silk in its abdomen. The spider will tap the ground with the end of its abdomen before jumping, attaching a silk strip, and when it jumps up, the abdomen will always pull the silk, just like the Spider-Man in the movie swinging in the New York building. If the spider does not jump to its intended target and falls out of the air, the silk can be allowed to hang in the air, and the spider can pull the silk back to its original position, or rappel to the ground. Therefore, biologists call this silk a safety wire, like a safety rope used when climbing rocks.
Marvel Spider-Man (Marvel Spider-Man vol.4 #1封面)
However, biomechanics with a strong physical background have questioned this claim. From a human point of view, falling from a position dozens of times higher than one's own body is of course a terrible thing. However, the body of the jumping spider is small and light, and the air resistance has a great impact on it, and the terminal speed of the fall should not be fast, even if it falls from a high altitude, it may not be injured. Is it possible that this wire actually has other functions?
The first person to study this problem was a high school student, Chen Yongkang. When he was in Taichung First High School, he was very interested in the behavior of jumping spiders, so he asked Dr. Kairong Ji, who teaches in the Department of Physics at Chung Hsing University, to direct the research. Dr. Kai-Yung Ji is a special topic advisory professor at my university, and together we have collaborated to discover the fastest known speed of biological motion. Unfortunately, when Chen Yongkang entered the laboratory, I was still in junior high school and did not have the opportunity to meet. Many of the things that jumped spider research were later heard by Teacher Ji. Chen Yongkang and Ji Kairong and others used a common jumping spider on campus, Hasarius adansoni, as experimental subjects, and raised 27 jumping spiders in the laboratory. He then designed an indoor jumping platform for the spider and used a high-speed camera to record the jumping process of Anderson's fly tiger. Interestingly, he found that 5 of the jumping spiders did not draw wire from the starting point when jumping. In this way, there is a control group, and the effect of drawing or not on the jumping movement of the spider can be compared. After comparing the films that jumped between the two, the research team discovered an important function of this silk thread: balance.
balance! This is a popular project in the field of biomechanics. Don't look at how easily we humans can balance when walking, running, or jumping, for robots, balance is very difficult, especially jumping. Once the opposite direction of the force is not through the centroid when jumping, the body will rotate in the air, and it is difficult to land smoothly. A similar thing happened to the jumping spider observed by Chen Yongkang and others in the laboratory, where the spider without brushing would lose its balance in the air and finally fall on the target. In contrast, there are brushed jumping spiders, they can maintain a certain posture in the air, stabilize their bodies before landing, and land smoothly.
Photo: The Importance of Balancing Silk when Jumping Spider Jumps (Manga/Eun Yu Zhen)
Experimental results show that whether the spider is drawn or not, it can jump out of similar height and distance, but the individuals with the wire show higher lag time, horizontal deceleration and balance. The difference between the two landing situations is the most obvious, the individual with the brush is the horizontal posture behind the head and feet, the average only 0.01 seconds can stand steady, while the individual without the brush is in the vertical position of the head and feet to fall to the ground, it takes an average of 0.05 seconds to stand firm. The price of drawing and stabilizing the body is to consume more mechanical energy. Jumping spiders without brushing are mainly affected by air resistance in the air, and lose 33% of their mechanical energy before landing. The brushed spider loses 76% of its mechanical energy due to the change of the elevation angle through the force applied to the silk thread, together with the effect of air resistance. Understanding this result from a biological point of view, it will be found that whether the jumping spider can land smoothly, which greatly affects the ability to prey, and the fall of the head and feet is obviously difficult to catch the prey. If the jumping spider is dodging predators, it takes 5 times the time to stand firm, and it may also be captured by predators.
This finding proposes a third mechanism for the balanced way animals jump. In the past, biomechanics classified jump balance into two types, namely the swing of the limbs and the swing of the tail, both of which rely on the principle of conservation of angular momentum, which generates angular momentum in the air through limb movement, and then makes the body axis produce the opposite angular momentum to maintain balance. The balance used by the jumping spider does not belong to either of these two, but pulls the ground through the spider silk, creating additional rotation, so that the spider does not need to swing its limbs sharply or evolve a thick tail.
Figure/Anderson fly tiger landing process (a) Individuals with pulled balance wires (b,c) Individuals without pulling balance wires (Chen et al. 2013)
The findings were published in 2013 in the Journal of the Royal Society Interface under the title "More than a safety line: jump-stabilizing silk of salticids.", link: https://doi.org/10.1098 /rsif.2013.0572。
The study has attracted the attention of both spider scientists and biomimetics and is currently cited 19 times (Google Academic statistics). This result broke the existing cognition of biologists, showing that the silk thread pulled by the jumping spider before taking off was not only for safety, but more importantly, it helped the jumping spider balance its body in the air, and greatly affected its predation rate and chance of escape. From the list of papers citing this study, it can be found that this biomechanical study inspired at least two research teams to design jumping robots. Here's a video released by one of the teams, whose jumping robots encountered an unbalanced problem in the air. After making a balance wire for the robot, it can land safely.
Video: Jumping Robot Inspired by Spider Balance Silk (Shield et al. 2015)
The last paragraph of this film is a jumping robot pulling a balance wire, and the picture stops abruptly at the moment of smooth landing. I think it's possible that the robot will bounce and flip next, so stopping here, it is likely that there will be a buffer mechanism when landing, but at least it can solve the problem of flipping in the air.
To my surprise, another study citing this paper was conducted on the International Space Station. The study originated in a campaign for the Space Station Experiment, where it was proposed to test whether jumping spiders could prey in microgravity, and was adopted by the organizers. So two jumping spiders were taken to the International Space Station, where one of the individuals successfully jumped up and captured a fruit fly floating in the air. Interestingly, it also had a brush before taking off and used this wire to return to the surface of the container after catching fruit flies. Although this behavior can not see whether the silk thread still plays a balanced role, it does make the security wire worthy of the name. Now that we have our own space station, I don't know when we can take the jumping spider up and jump again?
Photo: Jumping spider taken to the International Space Station for predation experiments (David 2016)
Citations:
Chen, Yung-Kang, et al. "More than a safety line: jump-stabilizing silk of salticids." Journal of The Royal Society Interface 10.87 (2013): 20130572.
Shield, Stacey, Callen Fisher, and Amir Patel. "A spider-inspired dragline enables aerial pitch righting in a mobile robot." 2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS). IEEE, 2015.
Hill, David E. "Jumping spiders in outer space (Araneae: Salticidae)." Peckhamia 146 (2016): 1-7.
Further reading:
Termites' ultra-high-speed bounce --- the fastest known speed of motion of a creature | Guan Guanzhi
Background: The author of this article, Guan Guanzhi, graduated from the Department of Entomology of Chung Hsing University in Taiwan and is currently studying Applied Economics at Chung Hsing University. The author authorized the debut of Voice of the Storm.
Editor-in-Charge: Sun Yuan