While most spiders live a solitary life, Anelosimus eximius knows there is strength in numbers.
The arachnids, native to the tropical forests of French Guiana, spin basket-shaped webs that can reach the size of a small house. When prey is ensnared in their massive web, thousands of quarter-inch-long spiders descend in a synchronized attack. Working as a group, the spiders can take down prey like moths and grasshoppers hundreds of times their size.
Of the roughly 50,000 known spider species known to science, only a handful opt to live and hunt in groups, and little is known about their coordinated behavior. New research published in Proceedings of the National Academy of Sciences reveals that the spiders use vibrations in their massive web to coordinate their kills. Notably, the spiders decide whether they attack prey based on the vibrations from the prey, and vibrations from other spiders in the colony, reports Maggie Galloway for Popular Science.
To learn more about how the species hunts, researchers tested the webs of two colonies of Anelosimus eximius. The team mimicked the action of prey getting entangled by creating different vibration patterns on the web, and filmed the spiders’ reactions. When scientists slowed the video down, they found that the spiders would occasionally stop, then start again in synchrony as they approached a meal.
"When the prey falls in the web, this triggers the movement of the spiders," says study author Raphaël Jeanson, an ethologist at the Center for Integrative Biology in Toulouse, says to Live Science’s Cameron Duke. "But after a while, they all stop for a few milliseconds before they start moving again."
Jeanson and his colleagues hypothesized that if too many spiders are moving toward prey at once, it might produce too many vibrations and drown out the weak signal from the struggling meal. By synchronizing their start and stop times as they approach the prey, the spiders are better able to sense the trapped insect.
When they analyzed the result of their vibration test with a computer model, the team found the spiders were better at catching prey with their red-light–green-light approach than if they did not move in synchrony. The researchers also found that spiders needed to synchronize to sense smaller prey items in the web. But when the meal was instead a large, thrashing insect, the arachnids didn’t need to harmonize to sense it.
“It’s like in a room with people who are chatting,” says Jeanson to Jason Bittel for National Geographic. “If there is just a small, very faint noise, everybody needs to be quiet to hear it. But if there is a big explosion, you don’t need to be silent to detect it.”