Spatio-temporal patterns of preys and wastes moved by ants within the nests

Living in society in a restricted and confined nest implies important organisational issues. Ants have to control food supply for the whole colony as well as nest defence but they also have to manage everyday life tasks such as waste rejection. Within the nest, ants are faced with different items that have to be used or rejected regarding colony needs. We study whether they can discriminate between three types of items (building material, nestmate cadaver or prey) and accordingly adapt the spatio-temporal distribution of these items. Therefore, we used colonies of the ant Myrmica rubra settled in a 2-dimensional space and introduced different items in the nest centre. We show that each item triggers a specific cascade of behaviour. We observed important differences in rejection time: building items were removed within a few minutes and cadavers after a few hours while preys could be kept in the nest for a day or more. Furthermore, the movement of items by ants leads to specific spatio-temporal patterns. Building items were removed with a straight trajectory from the centre to the exit of the nest. Ant cadavers that could bear pathogens showed a trajectory avoiding and moving away from larvae that are potentially more sensitive to diseases. The moving of preys headed an oscillating pattern: these items were alternatively taken on larvae for consumption and then moved away from them, until final rejection. This specific pattern may be due to the coupled effects of groups of ants acting alternatively to feed larvae and reject waste. In the case of cadavers and building items, only undertaking ants may be active. These results suggest that each ant is able to discriminate and interact with each other leading at the collective level to a complex cascade of behaviour.