Mobile Ad-hoc NETwork (MANET) is a collection of wireless mobile nodes which are connected in dynamic manner and these nodes acts as routers and communicate to each other. Due to this dynamic nature of MANET's, routing in MANET is extremely challenging, as it has limited bandwidth and power energy. MANET nodes operating on battery try to pursue the energy efficiency heuristically by reducing the energy they consumed. This paper reviews some on-demand routing algorithm for mobile, multi-hop ad-hoc networks. The algorithms are based on swarm intelligence and especially on the ant colony based meta heuristic.