| Stigmergy originated from the study of nest construction in termites and has been a model for self-organized systems. All current models of termite construction rely on this type of indirect communication between termites in the form of the chemical marking of work-product. We propose an excavation process that is governed solely by tactile interactions of termite excavators and patterns of traffic flow. Coptotermes formosanus Shiraki tunnels are bi-directional and radiate away from an origin. These vectors provide shared information that coordinates the labor of individuals. When excavation sites at the digging face of the tunnel tip were occupied by other termites, a queue of excavators awaiting access formed. Termites in queue responded to this delay by excavating soil from the tunnel wall. By examining excavation under conditions of high-flow and low-flow, we demonstrated that the rate of lateral excavation increased with queue length, a process we termed "digging pressure." This scales tunnel width to traffic flow.;The presence of a queue mediates branch formation. The likelihood that a depression became a branch was determined by competition between soil excavation enlarging it and deposition filling it in. When 3 mm by 3 mm depressions were positioned within a zone of tunnel near the tip, branches invariably formed, but when these depressions were further away from the tunnel tip, branches were less likely to form. Increasing the size of depressions did not greatly increase the likelihood of their becoming branches.;Coptotermes formosanus excavates through food sources in a process that results in the deposition of masticated food particles within tunnels in a manner previously shown for excavated soil. If soil Basidiomycota opportunistically invaded the microhabitat of fecal carton covered wood fragments along C. formosanus tunnels, then the basic mechanics of tunnel excavation through soil, when applied to a food source, serve as a preadaptation to evolution of the cultivation of fungi by termites. If, on the other hand, C. formosanus is exploiting fungi and fungal conditioned wood sequestered in tunnels, then a novel form of agriculture, perhaps the first to exist between fungus and insect, may be described. |
