The Ministry of Economy and Finance website's glossary of everyday economic terms includes the term Ringelmann effect. It refers to the psychological phenomenon in which individual contribution to performance decreases as more people participate in a group. It is a phenomenon proven by French agricultural engineer Maximilien Ringelmann in 1913 through tug-of-war experiments.
Ants are different. Although they live socially like humans, there are no free-riding members in tug-of-war. In humans, as a group grows, individual responsibility is dispersed and expectations of others arise, but ants faithfully perform their unique roles within the group, so when they form a group, both the group and the individuals become stronger.
◇showing superpowers when rolling leaves to build nests
Chris Reid and his research team at Macquarie University in Australia reported on the 13th in the international journal Current Biology that while human individual contribution decreases as more people participate, weaver ants increase individual strength as the group grows.
Weaver ants are distributed from African tropical regions to islands in the South Pacific. These tree-dwelling ants roll leaves and fasten the edges with silk produced by their larvae to make nests. Because they roll leaves much larger than themselves, cooperation among many ants is necessary. Reid said weaver ants can pull leaves much more strongly when working in groups than when working alone.
The research team collected six weaver ant (Oecophylla smaragdina) colonies of up to 5,000 individuals in northeastern Australia. When given leaf-shaped paper, they began rolling it as they do in nature. Thin wires were attached to the leaves. The wires were connected to force-measuring devices to measure the force the ants exerted. Ants pulled with a force about 60 times their body weight. But when moving as a group, each ant exerted a force equivalent to 103 times its body weight. In a group they become super ants.
Ringelmann discovered through tug-of-war experiments that people do less work as group size increases. Think of the tug-of-war in the Netflix drama Squid Game. More people mean greater strength, but free riders also appear. This is explained as a failure in motivation or role coordination.
Ants are known as an exception to the Ringelmann effect. For example, army ants carrying food in tropical forests can support more weight per individual when working together. This phenomenon is called "superefficiency." However, previous studies measured the collective strength of ants but did not measure the force exerted by individual ants as in this study.
◇showing superefficiency by faithfully performing individual roles
David Labonte, a co-author of the paper and professor at Imperial College London (ICL), proposed the hypothesis that the chains ants form when rolling leaves act like a ratchet that causes the chain to turn to one side. He said the ant chain works like a ratchet because each ant performs pulling motions and foot movements suited to its role.
First, one ant grabs the edge of the leaf, bends its legs, and pulls hard to start the leaf-rolling. The second ant grabs the waist of the first ant and straightens its legs to hold firmly. At this time, adhesive substances are secreted from the soles of the feet so the legs can stick firmly to the surface. This allows the front ant not to slip and to exert more force.
The adhesive force of the soles acts as an anchor that fixes the ratchet so the front ant does not slip and can exert a bit more force. When a third ant joins at the back of the chain, it assumes a fixed posture like an anchor, allowing the first two ants to exert greater force than when they work alone.
Recently, footage was released showing four-legged robots cooperating to pull heavy objects. It is not yet known whether the robots have overcome the Ringelmann effect. The researchers said the ants' soles that stick well to the ground and leg movements matched to roles improve the efficiency of ant groups and that this finding could help design and coordinate swarms of cooperative robots.
References
Current Biology(2025), DOI: https://doi.org/10.1016/j.cub.2025.07.038