euro-pravda.org.ua

Spiders maintain their running speed even when they lose two legs.

Some arthropods shed body parts, most commonly limbs, as a means of escaping predators. In biology, this process is known as autotomy. For instance, spiders can detach one or more of their legs, but they regenerate them during molting. A team of American arachnologists wondered how these creatures move after losing their limbs. For the first time, the researchers utilized machine learning to analyze spider movements and discovered that they do not relearn how to run; instead, they adjust their gait, enabling them to return to normal running.
Пауки сохраняют свою скорость, даже если у них отнимают две ноги.

Many animals, particularly arthropods and some vertebrates, possess a "superpower." They can spontaneously shed a part of their body when their life is at stake. When attacked by a predator, these animals "sacrifice" an unnecessary limb, which distracts the opponent and provides an opportunity to escape. This ability is known as “autotomy” — a common strategy in the animal kingdom.

Autotomy is especially frequently observed in spiders, which during this process can discard one or two legs (they have eight in total). However, the lost legs regenerate after molting — for instance, young individuals can regrow them in just one to two months.

Before their limbs regrow, spiders need to move around, hunt for food, and escape from predators. Previous studies have noted that losing limbs can slow down a spider's movement, which in turn affects their survival. Experts have debated for decades how arthropods compensate for the loss of legs and whether regeneration impacts their movement.

The question was explored by a team of arachnologists from the United States led by Suzanne Kane (Suzanne Kane) from Haverford College in Pennsylvania. The researchers studied how arthropods adapt their gait immediately after autotomy and during the molting period. The findings of the researchers are presented on the electronic archive website for scientific articles and preprints in biology, bioRxiv.org.

For their experiments, Kane and her colleagues selected young tarantulas of the species Davus pentaloris, raised in captivity and yet to lose any limbs. These creatures are found in Central America, primarily in Mexico and Guatemala.

Initially, the researchers filmed how the eight-legged spiders run on a flat surface using a high-speed camera. They then prompted each spider to discard two legs and repeated the filming immediately after the "amputation" and again after a day.

To induce the spiders to shed specific limbs, the researchers first "sedated" the animals by lowering the ambient temperature, then glued two selected legs to a piece of cardboard. When the spiders "woke up," the scientists lightly brushed them with a fine paintbrush, creating a stimulus that provoked the arthropods into autotomy.

To clarify, spiders do not sleep in the same way mammals do, but their activity is greatly influenced by the surrounding temperature. When the temperature drops, the spiders' metabolism slows down, resulting in reduced mobility: they become less active and sometimes nearly immobile, resembling a sleep or hibernation state. This is not a full "sleep," but rather an adaptive response that allows them to conserve energy in cold conditions.

Before the autotomy, the test animals ran at a speed of about 0.38 meters per second on all eight legs. After losing two limbs, they almost immediately returned to their previous performance levels. It turned out that even without two legs, the spiders run as fast as they did before.

Davus pentaloris

Video analysis showed that the arthropods redistributed the load onto the remaining limbs and altered the synchronization of their movements. For instance, they began placing their legs in the areas where the amputated legs used to be and adjusted their stride for greater stability. In other words, the animals instantly restructured their gait: the remaining six legs moved in a new manner, taking the place of the lost ones. This allowed them to maintain speed and stability.

After the "amputation," the spiders spread their remaining legs wider and turned their bodies 11-15 degrees relative to their direction of movement. This helped evenly distribute the load and maintain stability.

However, the main discovery was the instantaneous change in gait. Previously, scientists believed that after losing two legs, spiders switched to a "truncated tetrapod" gait (using four legs) or a "modified tripod" gait (using three pairs of legs). Machine learning, analyzing thousands of video frames, revealed that spiders combine both options, smoothly transitioning between them, with adaptation occurring instantly.

“Interestingly, after losing a limb, spiders do not relearn how to run — their nervous system immediately finds the optimal solution,” explained Kane.

The discovery by American arachnologists highlighted the incredible flexibility of spider nervous systems. Such adaptive skills may attract the interest of robotics engineers. They could develop machines that, like spiders, can quickly "reprogram" their movements after malfunctions. This is especially crucial for systems operating in extreme conditions — from disaster zones to other planets.