At a Los Angeles nail salon, Elle Woods introduced a nail technician named Paulette in the bend and snap: a foolproof method of getting someone’s attention, and the only move that yields an 83 percent return on a dinner invitation, at least in the universe of the’ Legally Blonde’ movies.
Now let the scorpion and its infamous tail introduce you to the bend and turn: perhaps an even better method of getting someone’s attention. If you are an insect, you can also expect a dinner invitation (with you on the menu).
The segments of a scorpion’s tail can move in many ways: bending up and down, twisting left and right, and bending and twisting at the same time. A new three-dimensional reconstruction of this aggressive body part reveals a special joint unique to the animal kingdom that allows for the bending and twisting of the tail. The study, which describes a structure many scorpion biologists were familiar with but never formally described, was published Wednesday in The Journal of the Royal Society Interface.
“No one has looked at the structure that makes this deadly weapon move so precisely in space,” said Alice Günther, a graduate student at the University of Rostock in Germany and author of the article.
“This study does a great job of really digging into the complexity of something that we’ve all observed but never quantified,” said Lauren Esposito, the curator of arachnology at the California Academy of Sciences, who was not involved in the study.
Scorpions have been for about 435 million years on Earth with a flexible, segmented body part called a metasoma. This area is commonly referred to as the scorpion’s tail, but technically it’s not a true tail because it doesn’t extend past the anus (rather, it contains the anus), according to Arie van der Meijden, a biologist at the Research Center in Biodiversity and Genetic Resources in Portugal. who was not involved in the investigation.
But we call them tails, and scorpions use them for everything important to an arthropod: killing, mating, digging, defecating and defending themselves. Some lusty scorpions engage in courtship rituals that involve patting and clubbing their tails, while other scorpions scrape their stingers against their bodies to create a rasping sound that deters predators, said Dr. Esposito, noting that “they have this incredible range of motion and flexibility that’s pretty amazing.”
dr. van der Meijden repeated that feeling. “If you try to wrestle with a scorpion, which I often do, they can almost twist their tails and sting 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 curlicue or a raccoon’s striped feather duster, a scorpion’s tail also contains the arthropod gut and ventral nerve cord, the invertebrate equivalent of a human spinal cord. So as a scorpion’s tail bends and twists, it also moves solid waste up its anus so it can poop through its tail.
dr. Esposito sees the tail as an “ingenious solution to limited body parts and mechanics,” but they admitted the scorpion’s stool logistics are “kind of bizarre.”
After identifying the unknown joint in 16 species of scorpions, the researchers selected a female Mesobuthus gibbosus, a camel-colored scorpion slightly shorter than a colored pencil, as a tail model. They scanned the scorpion’s metasome using a form of CT imaging and assembled the scans to reconstruct the tail in three dimensions. They then printed jumbo-sized 3D versions of each of the segments to test the real-life range of motion.
A scorpion’s tail is essentially a tube formed by five barrel-shaped segments that enclose the gut. The reconstruction showed that the first four segments are connected to each other and the middle part of the scorpion’s body via a previously undescribed joint. The back of each barrel has an opening where the front of the next segment can sit, twist and turn. dr. Günther compares it to a ball joint, only there is no socket. In a scorpion tail, there is only the ball, that is, the rounded edge of the joint.
The lack of a socket allows the segments of the tail to bend up and down and twist left and right, bending and twisting at the same time. A scorpion bends its tail as we would a finger, said Dr van der Meijden, demonstrating with his finger on a Zoom call. But it can also twist its tail like a chain, he said, wincing when he personally demonstrated that a human is incapable of twisting a finger.
The researchers called this joint a “sliding-rolling pair” because the segments shift during rotation and could roll during bending.
But this important question — whether the joint slides against the connecting segment or rolls like a wheel — remains unanswered, said Dr. van der Meiden. “When you roll, the position of the joint changes,” he said. “And sliding would put more wear on the joint.” dr. van der Meijden said this question could easily be 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 bend, not twist. But the rest of the tail is so good at bending and twisting that twisting the last segment would be unnecessary, the authors write.
Of the more than 2,000 species of scorpions known to science, many have vastly different tail types. Some, like the flat rock scorpion, have long and thin tails like trains of ziti. Others, like the aptly named fattail scorpion, have more junk in their trunks. But many probably know the same trick: bend and twist.