Stigmergy, self-organization, and sorting in collective robotics

Many structures built by social insects are the outcome of a process of sel f-organization, in which the repeated actions of the insects interact over time with the changing physical environment to produce a characteristic end state. A major mediating factor is stigmergy, the elicitation of specific environment-changing behaviors by the sensory effects of local environmenta l changes produced by previous behavior. A typical task involving stigmergi c self-organization is brood sorting: Many ant species sort their brood so that items at similar stages of development are grouped together and separa ted from items at different stages of development. This article examines th e operation of stigmergy and self-organization in a homogeneous group of ph ysical robots, in the context of the task of clustering and sorting Frisbee s of two different types. Using a behavioral rule set simpler than any yet proposed for ant sorting, and having no capacity for spatial orientation or memory, the robots are able to achieve effective clustering and sorting sh owing all the signs of self-organization. It is argued that the success of this demonstration is crucially dependent on the exploitation of real-world physics, and that the use of simulation alone to investigate stigmergy may fail to reveal its power as an evolutionary option for collective life for ms.