When asked if ants rest or if they work untiringly all day long, most people would probably respond that they had no idea. In fact, when watching the bustling life of an ant hill it is hard to imagine that ants take a rest from now and then. However, biologists discovered that ants rest quite a large fraction of their time. Surprisingly, not only single ants show alternate phases of resting and being active, but whole ant colonies exhibit synchronized activity phases that result from self-organization. Inspired by this self-synchronization behaviour of ant colonies, we develop a mechanism for self-synchronized duty-cycling in mobile sensor networks. In addition, we equip sensor nodes with energy harvesting capabilities such as, for example, solar cells. We show that the self-synchronization mechanism can be made adaptive depending on the available energy.