Negative feedback: ants choose unoccupied over occupied food sources and lay more pheromone to them

In order to make effective collective decisions, ants lay pheromone trails to lead nestmates to acceptable food sources. The strength of a trail informs other ants about the quality of a food source, allowing colonies to exploit the most profitable resources. However, recruiting too many ants to a single food source can lead to over-exploitation, queuing, and thus decreased food intake of the colony. The non-linear nature of pheromonal recruitment can also lead colonies to become trapped in suboptimal decisions, if the environment changes. Negative feedback systems can ameliorate these problems. We investigated a potential source of negative feedback: whether the presence of nestmates makes food sources more or less attractive. Lasius niger workers were trained to food sources of identical quality, scented with different odours. Ants fed alone at one odour. At the other odour ants fed either with other feeding nestmates, or with dummy ants (black cuticular hydrocarbon-coated glass beads...