Instead of slacking off like people in big groups, these ants double their pulling power by splitting roles — some anchoring while others pull. Scientists call it a “force ratchet,” a strategy that makes their chains stronger with each new member.

Ant Teams Defy Age-Old Problem

Weaver ants appear to have cracked a teamwork challenge that has troubled people for centuries: when human groups get larger, individuals usually put in less effort. New findings reported in Current Biology reveal that weaver ants do the opposite, with each ant becoming stronger as the group expands.

This decline in human effort was first described by French engineer Max Ringelmann in 1913. In experiments measuring students pulling ropes, he discovered that although the total pulling force increased as more participants joined, the individual effort from each person decreased.

Ringelmann’s observation has since been seen in countless settings, from office committees to sports teams. Yet according to behavioral ecologist Madelyne Stewardson of Macquarie University, who led the recent study, weaver ants improve their cooperative nest-building as more members join the effort.

Outperforming the Ringelmann Effect

“Each individual ant almost doubled their pulling force as team size increased – they actually get better at working together as the group gets bigger,” says Ms. Stewardson.

The research shows that these ants form highly efficient teams where individuals increase, rather than decrease, their contributions as the group expands.

Weaver ants (Oecophylla smaragdina) are small, tree-dwelling insects that live in tropical regions of Africa, Asia, and Australia. They are famous for constructing aerial nests by linking their bodies into chains to fold leaves and fastening them together with silk produced by their larvae.

Measuring Ant Power in Action

Stewardson and behavioral ecologist and supervising co-author Dr. Chris Reid from Macquarie’s School of Natural Sciences worked with an international team to measure and analyze the force different-sized ant teams could apply while building their nests.

The researchers set up experiments enticing weaver ant colonies to form pulling chains to move an artificial leaf connected to a force meter.

“The ants split their work into two jobs: some actively pull while others act like anchors to store that pulling force,” says Stewardson.

How the Force Ratchet Works

Co-lead author Dr. Daniele Carlesso from the University of Konstanz and Max Planck Institute of Animal Behavior in Germany, who was a PhD student at Macquarie during the research, says the team developed a theory called the ‘force ratchet’ to hypothesize how this works.

“The job each ant performs depends on its position in the chain,” says Dr. Carlesso. “Ants at the back of chains stretch out their bodies to resist and store the pulling force, while ants at the front keep actively pulling.”

“No one has looked into using a similar method as that used by the ants in order to generate force in swarms of multi-legged robots, but we plan to do this.”

Dr. David Labonte from Imperial College London, co-author on the paper, says the team found this method was key to increasing the contribution per individual as the team got bigger.

“Longer chains of ants have more grip on the ground than single ants, so they can better resist the force of the leaf pulling back,” says Dr. Labonte.

“The long chains effectively store the pulling force from individual ants in friction — together, the team seems to work like a ratchet.”

From Ant Hills to Robotics Labs

Dr. Reid says apart from delivering a fascinating insight into the natural world, the discovery could also help scientists design better robot teams.

When working in teams, current robots can only output the same force they do when alone, achieving at best a linear increase in force output. Weaver ants show there’s potential for much more.

“No one has looked into using a similar method as that used by the ants in order to generate force in swarms of multi-legged robots, but we plan to do this,” says Dr. Reid.

Related work has already shown that robots with more legs on the ground, inspired by millipedes, can perform better on complex terrain.

“Programming robots to adopt ant-inspired cooperative strategies, like the force ratchet, could allow teams of autonomous robots to work together more efficiently, accomplishing more than the sum of their individual efforts,” says Dr. Reid.