How Scorpion Tails Do the Bend and Twist

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At a Los Angeles nail salon, Elle Woods introduced the bend and the snapshot to a nail designer named Paulette: a foolproof way to grab someone’s attention and the only move that makes an 83 percent return on a dinner invite at least in the universe of “Legally Blonde” films.

Now let the Scorpio and its infamous tail introduce you to the bend and twist: perhaps an even better way to get someone’s attention. If you are an insect, you can also expect an invitation to dinner (with you on the menu).

A scorpion’s tail segments can move in many ways: bend up and down, twist left and right, and bend and twist at the same time. A new three-dimensional reconstruction of this aggressive body part shows a special joint that is unique in the animal kingdom and enables the tail to be bent and twisted. The research, which describes a structure familiar to many Scorpio biologists but never officially described, was published in the Journal of the Royal Society Interface on Wednesday.

“Nobody has looked at the structure that allows this deadly weapon to move so precisely in space,” said Alice Günther, doctoral student at the University of Rostock in Germany and author of the paper.

“This study does an excellent job of examining the complexities of something we all observed but never quantified,” said Lauren Esposito, curator of arachnology at the California Academy of Sciences who was not involved in the research.

Scorpios have been scurrying around the earth with a flexible, segmented body part called a metasoma for around 435 million years. This area is commonly known as the scorpion’s tail, but technically it’s not a real tail as it doesn’t extend beyond the anus (it contains the anus), according to Arie van der Meijden, biologist at the Research Center for Biodiversity and Genetic Resources in Portugal. who was not involved in the research.

But we call them tails, and scorpions use them for everything important to an arthropod: killing, mating, digging, dropping, and defending. Some lustful scorpions perform courtship rituals in which they tap and club their tails, while other scorpions scratch their spines against their bodies to make a scratchy sound that scares off predators, said Dr. Esposito, noting that “they have this incredible freedom of movement and flexibility”. that’s amazing. “

Dr. van der Meijden repeated this opinion. “If you try to wrestle with a scorpion, which I often do, they can almost turn their tail and stab you in all directions,” he said.

The tail becomes even more amazing when you consider that it is an extension of the Scorpion’s segmented body. Unlike a pig’s flourish or a raccoon’s striped feather duster, a scorpion’s tail also contains the bowel and ventral nerve cord of the arthropod, the invertebrate equivalent of the human spinal cord. So while a scorpion’s tail is doing the bend and twist, it is also moving solid waste towards its anus so it can pass through its tail.

Dr. Esposito sees the tail as an “ingenious solution to restricted body parts and mechanics,” but they admitted that the Scorpio’s defecation logistics are “kind of bizarre”.

After identifying the unknown joint in 16 species of scorpion, the researchers selected a female Mesobuthus gibbosus, a camel-colored scorpion slightly shorter than a crayon, as the tail model. They scanned the scorpion’s metasoma with some form of CT imaging and put the scans together to reconstruct the tail in three dimensions. Then they printed jumbo-sized 3-D versions of each of the segments to test the range of motion in real life.

A scorpion’s tail is essentially a tube made up of five barrel-shaped segments that encircle the intestines. The reconstruction revealed that the first four segments are connected to each other and to the middle part of the scorpion’s body by a previously undescribed joint. The rear end of each barrel has an opening in which the front end of the next segment can sit, twist and turn. Dr. Günther compares it to a ball joint, only that there is no pan. In the case of a scorpion tail, there is only the ball, i.e. the round edge of the joint.

The lack of an outlet allows the segments of the tail to bend up and down and turn left and right, as well as bend and turn at the same time. A scorpion bends its tail like we could bend a finger, said Dr. van der Meijden and demonstrated with his finger on a Zoom call. But it can also twist its tail like a chain, he said, flinching as he personally demonstrated a person’s inability to twist a finger.

The researchers called this type of joint a “sliding roller pair” because the segments slide when twisted and roll when bent.

But that key question – whether the joint slides against its connecting segment or rolls like a wheel – remains unanswered, said Dr. van der Meijden. “When you roll, the position of the joint changes,” he said. “And sliding would wear the joint more.” van der Meijden said this question could be easily answered by taking a close-up video of a live scorpion.

The fifth, last segment in a scorpion’s tail is narrower than the rest and can only be bent, not twisted. But the rest of the tail is so good at bending and twisting that twisting the last segment would be superfluous, the authors write.

Of the more than 2,000 species of scorpion known to science, many have very different tail types. Some, like the flat rock scorpion, have long and thin tails like ziti-like features. Others, like the aptly named fat-tailed scorpion, have more trash in their trunks. But many probably know the same trick: bending and twisting.