Spider Societies: Huddling Together Makes Spiders Bolder and Better at Hunting

Adult spiders huddling with their young in a nest. Noa Pinter-Wollman

Almost all spiders, big or small, are solitary critters. But some, like the Stegodyphus dumicola, live in bustling communities. They build vast nests together and hunt in groups.

Scientists investigating these spiders have unraveled some of the mysteries of their miniature societies. Watching traits like boldness and shyness develop revealed a fluid world of changing personalities and group dynamics.

"Most mathematical or computational models of animal collective behavior assume that all the individuals...have the same traits and follow the same rules of interaction," study author Edmund Hunt, who performed the study while at University of California, Los Angeles, told Newsweek. But in reality, he explained, individual animals can be highly influential within their social groups.

Just a single bold S. dumicola spider can improve its entire community's hunting skills. "Somehow that individual is a catalyst for effective group behavior…but what happens to the group if that important, keystone individual is lost?" Hunt, who now works at the University of Bristol, said.

To answer the question, Hunt and colleagues collected social spiders from roadside trees in South Africa and studied their behavior over six and a half weeks. They reported their results in the journal Proceedings of the Royal Society B: Biological Sciences.

The researchers measured the creatures' boldness regularly by simulating the approach of a bird with small puffs of air. In response, the critters tucked in their legs and stopped moving. The bolder the spider, Hunt explained, the quicker it would start to walk again.

The team compared how boldness changed in groups initially made up of all shy spiders, all bold spiders and a mixed group with all but one shy spiders. Over six weeks, the team tested the creatures' boldness and mapped their interactions with each other: the way spiders huddled together.

Researchers discovered these social interactions appeared to boost boldness—particularly in those spiders that huddled with daring neighbors. But boldness itself didn't make spiders more likely form interactions.

Two weeks into the experiment, the average boldness within each group was the same. Social interactions appeared to influence boldness so much that the artificial societies began to look like those you would find in nature.

Overall boldness decreased over time, which researchers think suggests the personality trait doesn't last that long within a group. Nonetheless, the creatures pick it up from each other remarkably quickly. "The individual trait shapes the group dynamics, but then the group can shape individual traits," Hunt said. "Collective behavior is not a purely 'bottom up' phenomenon."

These dynamics, the team think, offer a crucial way for groups that lose their powerful keystones to create further daring leaders. Being able to adapt to adversity, after all, is vital for a group's success. "Evolution by natural selection tends to produce animal groups that are robust to the knocks of an inhospitable world," he explained.

But don't worry if you find the prospect of increasingly bold groups of spiders terrifying. Their group dynamics seem "exquisitely balanced," Hunt said. It's important for the spiders to have a shy members, as well as bold, in their miniature societies. "Shyer individuals fulfil important functions too, like shared rearing of the young spiderlings. Like human beings, a good balance of personality types in a group makes their miniature society effective."