 on an optimum route to food sources, while maintaining back-up routes that can be used in the case of overcrowding or other obstacles. Ants use a method of communication called stigmergy, in which each ant modifies its local environment by laying down a chemical trail of pheromones and other ants respond to these modifications in such a way that the global behaviour of the colony becomes coordinated. Because the pheromone is volatile, and the intensity decays naturally with time, short, fast and often used routes will have a higher pheromone intensity than long, slow, blocked or abandoned routes, and will therefore be more often used and reinforced. Adaptation and improvement of existing routes, as well as the discovery of new routes, arises as a result of a degree of randomness inherent in the process. Some key elements of MANET routing algorithms inspired by this biological system are summarised in Table 14-1. While some ant colony inspired routing algorithms use either reactive or proactive strategies alone to gather information, combining these two approaches, and adding stochastic routing, results in a system that more closely mimics biological ant behaviour. It remains a challenge to minimise the bandwidth overhead used by the route sensing ant-agents, but algorithms that explicitly imitate aspects of ant behaviour may prove to be a key enabler for large-scale mesh networking. Leading Edge Wireless Networking Technologies Table 14-1: Features of Ant Colony Inspired MANET Routing Algorithms Routing feature Description Pheromone tables A table of routing information maintained in each node of the mesh, which indicates the "goodness" of the link to each of its neighbours in terms of data packet delivery time and number of hops to a destination. Reactive routing Software agents, unsurprisingly called ants, are generated information gathering to update pheromone tables in response to events such as a new station joining the mesh or the failure of a previously reliable route. Typically a "forward ant" seeks out 