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

TL;DR

This study demonstrates that ants can exhibit Braess's paradox, where choosing the shortest path leads to slower overall travel, due to collective exploration-exploitation dynamics rather than selfish behavior.

Contribution

The paper provides experimental evidence and a quantitative model showing that cooperative ant colonies can display Braess's paradox without individual selfishness.

Findings

Ant colonies favor the shortest path even when it slows the colony.

A model explains how evolutionary forces can lead to suboptimal global states.

The paradox arises from exploration-exploitation trade-offs in collective behavior.

Abstract

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.