A Mobile Ad hoc Network (MANET) is a collection of autonomous self-organized nodes. They use wireless mediu m for co mmunicat ion, thus two nodes can communicate directly if and only if they are within each other"s transmission radius in a mu lti-hop fashion. Many conventional routing algorithms have been proposed for MANETs. An emerg ing area that has recently captured much attention in network routing researches is Swarm Intelligence (SI). Besides conventional approaches, many new researches have proposed the adoption of Swarm Intelligence for MANET routing. Swarm Intelligence (SI) refers to complex behaviors that arise fro m very simp le individual behaviors and interactions, which is often observed in nature, especially among social insects such as ants, bees, fishes etc. Although each individual has little intelligence and simp ly follows basic rules using local in formation obtained fro m the environ ment. Ants routing resembles basic mechanisms fro m distributed Swarm Intelligence (SI) in b iological systems and turns out to become an interesting solution where routing is a problem. Ants based routing is gaining more popularity because of its adaptive and dynamic nature. A nu mber of Swarm Intelligence (SI) based algorithms were p roposed by researchers. In this paper, we study bio-inspired routing protocols for MANETs.