In order to avoid being eaten by their "wives", these male spiders have come up with all kinds of magical operations

In the laboratory of the School of Life Sciences of Hubei University, two spiders were hanging on the spider silk, so sweet... But the sweetness didn't last long. In an instant, the male spider broke free from his wife's arms at a speed of 90cm per second and flew freely into the air. The little spider also spun in the air, as if shouting: I didn't expect it, this is my escape route!

(Animated image) Source: Document 1

People who don't understand the situation clearly probably think that the male spider is an irresponsible scumbag... In fact, it is more of a scumbag trying to escape (although it is also a bit of a scumbag), because if it jumps away a second later, it might become the female spider's meal.

Part 1

Why did the spider run away?

Being eaten after mating is especially common among insects and arachnids. This behavior is called sexual cannibalism in biology. The behavior of the male mantis "dedicating" the female mantis in "Black Cat Sheriff" is sexual cannibalism.

The quotation marks are because it does not really want to offer itself as a tribute to the female mantis. (See the article "Childhood Shadow: Did the male mantis in "Black Cat Sheriff" really volunteer to be eaten?") Similarly, almost no spiders are willing to be food. Who would want to be eaten alive? For most creatures, the instinctive reaction of the body when encountering danger is to escape.

At this point, most spiders that can run have already run, and only those that can't are eaten. The spider in this article naturally doesn't want to be eaten, but it chooses a different way to escape: high-speed ejection.

Image of a mating spider, Image source: Reference 1

However, because the spider ejects too quickly, ordinary cameras can't capture any details, and the afterimages captured can't be studied at all. So scientists got a high-speed HD camera plus a macro camera, and only then did they capture the HD image of the male spider ejecting at the moment.

Spider ejection frame by frame decomposition Source: Reference 1

You can see that the one on top is a male and the one on the bottom is a female. During mating, the male spider's tibiotarsal joint remains folded and pressed against the female's abdomen, like a compressed spring.

At the moment of mating, the joints immediately release the hydraulic potential energy that has been accumulated for a long time, convert it into kinetic energy, and eject it at a speed ranging from 30cm/s to 90cm/s, with an average ejection speed of 65.9cm/s. The ejected spider will spin gracefully in the air, like an out-of-control flywheel, with a rotation speed of up to 175 times per second (I don’t know if the spider will feel dizzy).

The joints are in a compressed state during mating. Source: Reference 1

Sometimes, the female spider wants to eat the other halfway through mating. At this time, with its keen spider sense, the male spider will take the lead to bounce away, then climb back onto the female spider to continue mating. If there is danger, it will bounce away again and mate again, repeating this process over and over again until mating is complete, up to 6 rounds.

The study recorded a total of 155 matings, 152 of which ended with the male spider successfully ejecting and escaping. Only three unlucky spiders failed to eject in time and became food. It seems that the survival rate is quite high, at least 97.4% of the male spiders can survive.

But scientists would not let these spiders escape the hungry mouth of a female spider so easily. For the sake of science, the researchers pressed 30 mating male spiders on the female spider, so that they could not escape at all and were eaten immediately.

This step of the experiment is not meaningless, because it is to prove that the ejection behavior does indeed avoid "sexual cannibalism". If there is no ejection, the male spider will die.

Part 2

Why does the male spider launch itself out so quickly?

Such agile movements are attributed to the spider's legs' hydraulic joints, which are filled with hemolymph instead of motor oil. When movement is needed, the muscles on the dorsal and ventral sides of the spider's forebody contract, increasing the pressure and compressing the hemolymph for ejection. The power source of the entire hydraulic system is the spider's heart, which provides power for the circulation of hemolymph.

Spider joints source: Reference 1

Image source: Document 3

The hydraulic transmission system of spider legs is highly efficient, which allows the spider to live a happy life. Since the spider hydraulic shutdown is so useful, humans must apply it to their own technology. Foreign scientists have designed a driving structure "Smart Stick" that mimics the hydraulic joints of spiders, as shown below.

Source: Document 1

The one above may not be very similar, but the one below is a step closer. Because it is hollow inside, it is lighter than the previous drive system.

Image source: Document 2

In addition, there are many designs of bionic spider legs. But so far, no machine has perfectly imitated spider legs. If there is an unmanned vehicle that can use hydraulic system to eject 50 body positions in an instant like the dragon's spider, and can land safely without any damage, it will be an amazing super machine.

Part 3

In addition to ejection, male spiders have other escape strategies

In order to avoid being eaten, the male Long-Lobelia spider chose to slingshot, a cool-looking escape posture. Other male spiders may not use this trick.

For example, before mating, the park spider will give the female spider a gift, a delicious meal. When the female garden spider sees the food coming to her door, she will eat it first. The park spider takes advantage of the female spider's distraction and quickly gets the job done, greatly reducing the chance of being eaten.

A more beautiful garden spider. Image source: inaturalist

The strange spider is even more powerful. Before mating, the male spider will directly tie up the other spider with spider silk. After mating, the male spider can leave without any scruples, while the female spider has to spend a while to break free from the spider silk that binds her body.

The binding of the strange spider Source: Document 4

Animals in nature are always beyond human imagination. In addition to the various spiders mentioned above, there are countless ways to escape. In short, in order to avoid being eaten, male spiders have really evolved various magical operations. If I have to choose, I still think the escape posture of the Longxi spider is cooler.

References:

https://www.cell.com/current-biology/fulltext/S0960-9822(22)00485-7

Sheng Chuang. Research on fluid-solid coupling calculation and hydraulic transmission mechanism of spider foot[D]. Jilin University, 2018.

https://link.springer.com/chapter/10.1007/978-3-642-33989-9_34

https://royalsocietypublishing.org/doi/full/10.1098/rsbl.2015.0957

Produced by: Science Popularization China

Author: Su Chengning

Producer: China Science Expo

The article only represents the author's views and does not represent the position of China Science Expo

This article was first published in China Science Expo (kepubolan)

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