What's going on at the entrance? A characterisation of the social interface in ant nests.

Nest entrances are key locations where information about environmental opportunities and constraints are shared between foragers and inner-nest workers. However, despite its functional value, we still lack a detailed characterisation of the interface between the nest and the environment. Here, we identified the social interface in the ant Myrmica rubra as being the population of ants that faced the nest entrance and that received significantly more contacts from returning foragers than other nearby ants. We also spatially delineated the entrance area that hosted the social interface, a 2-centimetre radius area from the nest openings, which influences the position, orientation, and behaviour of ants. Then, we studied the impact of additional entrances on this social interface as well as on the flow of foragers. The size of the social interface increased according to the number of open entrances through the progressive reorientation of the ants toward new openings. We also observed a significant, although less than proportional, increase in the flows of ants that were progressively distributed homogeneously between all open entrances. Thus, our work highlights the flexibility of both the social interface and the flow of foragers to changes in the numbers of passageways between the nest and the environment.