A little ant is walking on the sandy soil of Arizona looking for food. The food is meant for feeding the brood which is taken care of by other ants in the colony. Different ants have different tasks in the colony, and the ant we are following is going out of the nest every day in the search for food. The amazing aspect of ant colonies is that such a complex organization structure exists that is not controlled by the queen or a small group of bureaucratic ants. There is also no plan or to-do lists ants are following. No, the complexity of the ant colony is emerging out of the local interactions of ants. The ant we observe is following a trail of pheromones, indicating that other ants of the colony have found food nearby and dropped the pheromones on their way back to the nest. The use of pheromones is therefore a way of ants to communicate to others “follow my trail” and you may find food. The pheromone trail will evaporate at a certain speed, and will therefore only be of limited use. If other ants will not follow this trail, bring back food and add pheromones to the trail, the trail will disappear. But when the trail is enhanced by successful use of others, a highway of ants may emerge. On such a highway, we see one lane of ants empty handed following the pheromone signal, and the other lane of ants bringing food back to the nest.

There is an enormous diversity of ant-species, who have all have some differences in their social organization. Some ant-species have ant-colonies consisting of ants with different physical appearance dependent on their role in the colony: workers, foragers, soldiers, etc. In other ant-species, ants have all similar physical appearance and can switch roles. For example, when some foraging ants are killed by an ant-eater, the colony will experience a reduction of food being delivered by foraging ants, which is a signal for some ants to leave their caring for the brood role to a foraging role.

Ants change the environment which subsequently changes the behavior of other hands. This indirect influence of agents via the change of the environment is called stigmergy. Another example of stigmergy is the digital trails we develop when we interact with websites. By buying books, renting dvds or listening to music files we leave information “pheromones”. We get recommendations of other books, dvds or music that people “like you” also bought, rented or listen to. These stigmergic interactions can lead to a reinforcement of choices. Popular movies on featured on youtube tend to get even more viewers. If we want to understand how certain books, movies or songs become so popular, we need to look into the various ways choices are influenced and reinforced by others.