Accuracy of leadership and control of the audience in the pavement ant Tetramorium caespitum

In the ant species Tetramorium caespitum, collective foraging relies on group mass communication in which successful scouts lay a recruitment trail but also guide a group of nestmates to the food source. We conducted experiments to understand how group leaders may improve the success of recruits in reaching the food source and whether they adjust their leading behaviour to their audience, that is, to the following response of recruits along the foraging journey. We characterized the trajectories of leaders by measuring their straightness, angular deviation, maximal amplitude and walking speed. Trajectometric values highlighted that a straight path coupled with a slow walking speed increased the probability of followers reaching the food whereas leaders that walked at higher speed and deviated far from the food-nest beeline were more likely to lose recruits. Leaders did not seem to heed their audience since they did not reduce their speed or their path sinuosity after the loss of a recruit along their outbound journey. Information transfer about food resources by T. caespitum leaders is thus targeted towards a restricted number of recruits but without the informed individuals exerting any control over the following response of their audience. We discuss strengths and weaknesses of group recruitment compared with simpler or more sophisticated forms of information sharing and we debate the status of group recruiters regarding the concept of leadership in animal groups.