“Recent studies have shown that stigmergy is not necessary to explain concerted construction: Green et al. showed that worker aggregation rather than the previously suspected presence of cementation pheromone localized excavation work sites in termites, and Bruce found no behavioural response to freshly excavated soil that would contain a digging pheromone were it an organizing factor in excavation in leafcutter ants. Eciton army ants, which self-assemble into bridges to cross trail gaps, gauge the necessity to reinforce or leave these structures based purely on the rate of physical contact with passing workers with no evidence of stigmergic processes.”

Source : Infrastructure construction without information exchange: the trail clearing mechanism in Atta leafcutter ants | Proceedings of the Royal Society B: Biological Sciences