A mobile ad hoc network MANET is an autonomous collection of mobile users nodes that communicate over wireless links. Research interest in MANETs has been growing, and particularly the design of MANET routing protocols has gained a lot of significance. But constantly changing network topology, limited bandwidth and energy issues make the task of routing in MANETs a challenging one. Recently a new class of routing algorithms based on swarm intelligence has emerged. These algorithms are inspired from nature's self-organizing systems such as ant colonies, bird flocks and fish schools. The general characteristics of these biological systems which include their capability of self-organization, robustness, adaptation, self healing, and local decision making, make them a suitable source of inspiration for routing in MANETs. In this paper we provide a comprehensive overview of the nature inspired routing algorithms for mobile adhoc networks and compare them and also bring out their main merits and demerits.