Stigmergy
Termites build elaborate mounds without blueprints or leaders. Each agent follows simple local rules: pick up dirt where pheromone is low, deposit it where pheromone is high. Through this indirect coordination --- stigmergy --- order emerges from noise, and scattered particles coalesce into organized structures.
About this lab
Stigmergy, a term coined by French zoologist Pierre-Paul Grasse in 1959, describes a mechanism of indirect coordination in which the trace left by an action in the environment stimulates subsequent actions. In termite colonies, workers deposit soil pellets impregnated with pheromones. Other termites, sensing high pheromone concentrations, are stimulated to deposit their own pellets nearby. This positive feedback loop causes scattered material to aggregate into pillars, arches, and eventually the complex architecture of a termite mound --- all without any blueprint or central coordinator.
The key insight is that information resides in the environment, not in the agents. Each termite follows only local rules: wander randomly, pick up material from areas of low concentration, and drop material where concentration is high. The pheromone field serves as a shared, spatially distributed memory. As pheromones decay over time, unused sites fade while active sites strengthen, creating a dynamic balance between exploration and exploitation that shapes the final structure.
Stigmergy appears throughout nature and technology. Ant trail pheromones, wasp nest construction, and slime mold networks all rely on environment-mediated coordination. In computer science, ant colony optimization algorithms use virtual pheromones to solve combinatorial problems like the traveling salesman problem. This simulation implements the core mechanism: agents randomly walk on a grid, picking up and depositing particles based on local pheromone concentrations, demonstrating how complex spatial patterns emerge from purely decentralized, local interactions.