Stigmergy in action — ants find shortest paths via pheromone trails. Click to add food.
Ant colonies solve the shortest-path problem without central coordination. Each ant deposits pheromone proportional to path quality; shorter paths accumulate more pheromone per unit time, creating a positive feedback loop — stigmergy.
Ant colony optimization (ACO, Dorigo 1992) solves NP-hard combinatorial problems by mimicking stigmergy — indirect coordination through environment modification. The pheromone intensity on each path encodes collective memory of path quality without any individual ant understanding the global picture.