Pack hunting spiders are found in places other than your nightmares. While most spiders enjoy a solitary life, 20 of the approximately 50,000 known species of spiders live in colonies. One type , Anelosimus eximius, It lives in very large colonies of up to 1,000 individual spiders that work together to build webs spanning several metres. When they fall prey to their web, these social networks spiders They coordinate and attack their victim together, allowing them to take down much larger prey than they would if they hunted alone. Until now, the way these spiders carry out such coordinated attacks has been a mystery.
The study found that spiders use the vibrations in their massive webs to choreograph the choreography of a synchronized swarming process.
“The remarkable thing is that there is no leadership role among these spiders,” said Raphael Janson, a researcher at the Center for Research in Animal Cognition (CRCA) at the University of Toulouse in France and senior author of a new study on social spiders. . Instead, the entire spider colony coordinates its attack with each individual receiving the same information.
When attacking the colony, the spiders descend on their prey by synchronizing two phases of movement: approaching the struggling victim and standing still. This allows spiders to time their approach so that they each strike at once.
Using both field observations and computer simulations of this coordinated attack, Jenson’s team learned that the attack was directed almost entirely by vibrations in the shared web.
“When the prey falls into the web, it causes the spiders to move,” Jenson told Live Science. “But after a while, they all stopped for a few milliseconds before they started moving again.”
By luring spiders with a dead fly attached to the end of a vibration generator, the researchers showed that the hunting behavior was, in fact, the result of the struggle of helpless prey. However, this did not explain the coordinated movements of the colony.
For this, the scientists needed a computer model. The models revealed that while the vibrations of the prey might trigger the initial movement, it was the vibrations induced by the spider colony that enabled the predators to coordinate their attack. When each spider felt the vibrations from the prey, they began to walk. But the steps of hundreds of spiders meeting on a struggling insect also send vibrations through the web’s fibers, muffled sounds of a trapped meal.
“It’s a bit like when you’re in a room with people talking,” Jenson said. For a spider, every step you take makes a noise. Then they have to stop moving so they can listen to the prey, to make sure they are still going in the right direction.
The quieter the prey that is struggling, the more difficult it is for the spiders to coordinate stop-and-go movements. When the researchers vibrated the web and then removed the lure, the colony responded by moving toward the prey, but then each spider had to stop moving to “listen” for telltale signs of confusion. Scientists discovered that if the prey was vibrating intensely, the colony did not need to calm down, so it was less synchronized.
This study was published March 7 in the journal Proceedings of the National Academy of Sciences.
Originally published on Live Science.
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