Who are the ‘lazy’ ants? Inter-worker variation gives insight into potential functions of inactivity

Social insect colonies are commonly thought of as highly organized and efficient complex systems. And yet, social insects are also known to have high levels of worker inactivity. Not only is inactivity common, but a subset of workers effectively ‘specialize’ on inactivity, suggesting that inactivity does not result from constraints shared by all workers, such as a physiological need for rest. Some studies have tested potential links between inactivity and worker reproduction, worker age/ontogeny, and food storage, but very little is still known about adaptive functions or costs associated with this behavior. Here we concurrently test five separate but non-exclusive hypotheses for worker inactivity using behavioral, physiological, and morphological differences between inactive workers and their nestmates. Our data show that inactive workers have larger bodies, greater corpulence, limited task repertoires, spatial fidelity zones, and interactions with nestmates, suggesting that inactivity may be linked to slow pace-of-life, age polytheism, and acting as food stores. Simultaneous functions of inactivity may explain the difficulty in finding a simple answer to this complex question.