Observations on activity of ants of the species Leptothorax acervorum show that ants within the nest are inactive for about 72% of their time (Franks et al., 1990. Bull. math. Biol., 52, 597-612). By examination of the activity of individual ants it is demonstrated that activity bouts of individuals are highly synchronized. The bursts of activity detected by Franks et al. occurred three to four times per hour. In this paper we develop a model to describe the phenomenon. As a result of the interdependence of the number of active ants within the nest and the high level of community activity some predictions are made, which are supported by experimental data in a quantitative way. In case of starvation the number of active ants will increase and no rhythms should occur. When proportionally more brood is present the rhythms should occur with a higher frequency. Eventually the rhythm breaks down and a stable equilibrium is reached.