— Robotics researchers have studied robots that can follow the trails laid by other robots. We, on the other hand, study robots that leave trails in the terrain to cover closed terrain once or repeatedly. How to design such ant robots has so far been studied only theoretically for gross robot simplifications. In this paper, we describe for the first time how to build physical ant robots that cover terrain. We show that a modified version of node counting can model the behavior of the ant robots and report on first experiments that we performed to understand their behavior better. These experiments confirm that our ant robots indeed cover terrain robustly even if the trails are of uneven quality, the ant robots are moved without realizing this, or some trails are destroyed. Finally, we report the results of a large-scale experiment where ten simulated ant robots covered a factory floor of 25 by 25 meters repeatedly over 85 hours without any ant robots getting stuck.