Recruitment and entropy decrease during trail formation by foraging ants.

Abstract

Social insects utilise a complex spatial orientation system mediated by chemical signals. This study investigated how the foraging behaviour of ants (Dorymyrmex thoracicus) varies depending on the quantity of an available resource using a feld experiment. Further, we demonstrated computationally that ant displacement is compatible with a model based on pheromone deposition. Our experiment tested how the resource size (large or small) and availability (one or two simultaneous patches) of resources ofered infuence the number of recruited ants (trafc fow) and the speed of trafc fow both moving towards a resource and returning to the colony. The results showed that the returning fow was higher than the going fow independent of resource. The trafc fow towards a single resource was higher than the fow for either of two simultaneous resources patches ofered; thus, multiple resources sources split the fow, regardless of the fact that resource size did not afect foraging choices. Our results indicated that the ants used an orientation mechanism that can be reproduced by a theoretical computer model. With our model, we showed that initially, the displacement of ants followed no clearly detectable pattern. However, with increasing levels of ant recruitment and consequent pheromone deposition on the most used trails, returning displacement revealed the formation of shorter and more organised trails. The model revealed key transition between periods of order and disorder that continued until the fow of information reached an organised state (Shannon entropy). This study highlights an exceptional mechanism of foraging optimisation in eusocial insects.