Such problems can be solved by simulating the journeys of a swarm of trail-laying ants, Bonabeau's team suggests. Each 'virtual ant' marks the journey with a 'pheromone' that characterizes how short its tour was. Good routes become more attractive to other ants than poor routes. Simulating pheromone evaporation at a steady rate ensures that the colony does not get trapped onto mediocre solutions that prevent them from looking for better ones. ACO is currently being explored for planning petrol truck routes in Switzerland.
Ants generally move over open terrain.
Engineers are finding it useful to place their virtual foraging insects inside networks. This can help to identify, for example, the best way of routing signals through a communications network. The constant searching and feedback of the swarm makes this approach, 'Ant Colony Routing', highly flexible and responsive to changes such as removal or addition of channels to the network. British Telecom is exploring routing algorithms of this kind. One of the most intriguing applications of Swarm Intelligence is to the design of real robotic systems in which the robots are tiny devices that act collectively.