Udipta Chakraborti | Searcharxiv

arXiv2026

Braess's paradox in tandem-running ants: When shortest path is not the quickest

Braess's paradox -- where adding network capacity increases travel time -- is typically attributed to selfish agents. Although eusocial colonies maximize collective fitness, we find experimentally that \emph{Diacamma indicum} ants exhibit this paradox: Leaders favour the shortest path even when it slows the colony. We present a quantitative model of the exploration-exploitation trade-off, demonstrating that evolutionary forces selecting for shortest-path identification can force suboptimal global states. This proves the paradox can emerge in highly cooperative systems without individual selfishness.

physics.bio-ph↗

arXiv2025

A game played by tandem-running ants: Hint of procedural rationality

Navigation through narrow passages during colony relocation by the tandem-running ants, $\textit{Diacamma}$ $\textit{indicum}$, is a tour de force of biological traffic coordination. Even on one-lane paths, the ants tactfully manage a bidirectional flow: Informed individuals (termed leaders) guide nest-mates (termed followers) from a suboptimal nest to a new optimal nest, and then return to recruit additional followers. We propose that encounters between the ants moving in opposite directions can be modelled within the framework of game theory leading to an understanding of the mechanism behind observed behaviours. Our experiments reveal that, upon encountering a tandem pair (a leader and its follower) on a narrow path, the returning leader reverses her direction and proceeds toward the new nest again as if she becomes the leader guiding a follower. This observed behaviour is consistent with game-theoretic predictions, provided the assumption of perfect rationality is relaxed in favour of bounded rationality -- specifically, procedural rationality. In other words, the experimental outcomes are consistent with sampling equilibrium but not with Nash equilibrium. Our work, which strives to induct the essence of behavioural game theory into the world of ants, is first ever report of realizing sampling equilibrium in scenarios not involving human players.

nlin.AO↗