Vibrational communication in the spatial organization of collective digging in the leaf-cutting ant Atta vollenweideri

Subterranean ant nests are structures that emerge from collective building. The mechanisms used by individual ant workers to coordinate their building behaviour are largely unknown. We discovered that isolated workers of the Chaco leaf-cutting ant Atta vollenweideri stridulate while excavating in soil, and we investigated the possibility that workers communicate via vibrational signals in the context of collective nest excavation. Workers were observed to stridulate at similar rates, not only while manipulating soil with their mandibles, but also several seconds before grabbing the material. The measured attenuation rate suggests a detectable signal range of less than 6 cm. When presented with stridulation signals in an experimental arena offering distinct locations to excavate, workers were more likely to dig close to the source than at an alternative site. The probability of a worker digging at a location increased with the intensity of the vibrational signals produced at this location. Group-level stridulatory activity was monitored in the context of nest enlargement, in which ants excavating a tunnel were allowed suddenly to break into an existing chamber. Recordings before and after having gained access to the chamber showed that workers stridulated while excavating, but gradually discontinued signal production when nest space was available. Our results indicate that beyond the previously described use of vibrational signals in the contexts of food recruitment and alarm communication, workers stridulate while engaged in nest digging and attract nestmates to join excavation activity at the same location, thus contributing to the spatial organization of collective nest building.