Ant algorithms were rst proposed by Dorigo and colleagues [33, 40] as a multi-agent
approach to difcult combinatorial optimization problems such as the traveling sales- man problem (TSP) and the quadratic assignment problem (QAP). There is currently
much ongoing activity in the scientic community to extend and apply ant-based al- gorithms to many different discrete optimization problems [5, 21]. Recent applications
cover problems such as vehicle routing, sequential ordering, graph coloring, routing in
communications networks, and so on.