Heuristic rules for cooperative transport in wood ant nest maintenance.

Collective behaviour in ants includes cooperative transport where individuals control behaviour relative to an object. Some species show efficient collective food transport because individuals share directional information. It is less clear how individuals coordinate in tasks, such as movement of nest material, where movement direction is unclear. Wood ants build nests from twigs and leaf litter that require constant maintenance. We provoked such maintenance by placing sticks over nest entrances which ants removed by walking backwards aligned to the stick. When ants cooperated, the second ant joined a moving stick more quickly and precisely than initial ants. Cooperation was further promoted by ants staying engaged for longer and making fewer grip adjustments when cooperation was effective. Although coordination was stochastic and imprecise, ants respond to local sensory feedback, with adjustments that promote cooperation. This suggests collective transport can emerge from simple and flexible sensorimotor heuristics.