Social animals display a wide range of behavioural defences against infectious diseases, some of which inherently increase social contacts with infectious individuals (e.g., mutual grooming), while others decrease them (e.g., social exclusion). These defences often rely on the detection of infectious individuals, but this can be achieved in several ways that are difficult to differentiate. Here, we combine non-pathogenic immune challenges with automated tracking in colonies of the clonal raider ant to ask whether ants can detect the immune status of their social partners and to quantify their behavioural responses to this perceived infection risk. We first show that a key behavioural response elicited by live pathogens (allogrooming) can be qualitatively recapitulated by immune challenges alone. Automated scoring of interactions between all colony members reveals that this behavioural response increases the network centrality of immune-challenged individuals through a general increase in physical contacts. These results show that ants can detect the immune status of their nestmates and respond with a general “caring” strategy, rather than avoidance, towards social partners that are perceived to be infectious. Finally, we find no evidence that changes in cuticular hydrocarbon profiles drive these behavioural effects.

Survival of individuals was scored manually. Grooming received by focal ants was manually scored from video recordings using BORIS software 5.1.0. Other behavioural metrics were calculated from automatedly tracked trajectories of all ants recorded with the tracking software anTraX. Mass spectra of cuticular hydrocarbons were acquired and analysed with the software ChemStation G1701AA v. A.03.00.