Having robots form mobile ad hoc networks is a promising approach when deploying robot swarms in environments lacking global communication and navigation infrastructures. We propose a decentralised controller that enables robot swarms to form mobile ad hoc networks between multiple locations of interest. The controller is designed to minimise the length of the established networks, helping to reduce the number of robots required for the network, and the costs associated with communication and navigation along the network. Through physics-based simulations and real-robot experiments, we demonstrate that the controller yields networks that are significantly shorter in length than centrally computed optimal starlike trees, and that compare reasonably well with centrally computed minimal-length networks (i.e. Steiner trees). Moreover, robots not required for maintaining the network become available for performing tasks at the locations of interest. The findings could pave the way for energy-efficient deployment of robot swarms in a range of environments from underground to outer space.