Ants’ survival and waste management in Myrmica rubra nests

Sociality increases risks of disease transmission as genetically related individuals live in a confined environment. Therefore, social insects developed specific defences against pathogens by showing hygienic behaviours such as the rejection of cadavers and other wastes. We investigated if the undertaking and waste management is actually an efficient way of increasing ants’ survival and of limiting pathogens transmission. First, we observed the survival curve of ant colonies that were prevented from rejecting their dead nestmates outside the nest. Colonies that were forced to keep their dead inside the nest showed increased mortality of both adults and larvae in comparison to control nests, confirming that undertaking is an effective way for improving colony’s survival. Then, we compared the rejection dynamics of single waste items (ant cadavers, preys and clay pellet) introduced into ant nests. Clay pellets were quickly rejected within 12 ± 4 minutes, cadavers were dumped outside after 139 ± 28 min and preys were eaten and rejected only after 17.3 ± 0.3 hours. Spatial localisation inside the nest also differs between different items, as most cadavers stayed far from ants’ aggregate and larvae while preys were long-eaten close to larvae and inside ants’ aggregate. These results show that cadavers and preys are managed differently before becoming contagious, thus preventing effectively pathogens transmission inside the nest.