Dynamics of nest excavation and nest size regulation of Lasius niger (Hymenoptera : Formicidae)

The adaptation of nest size to its population is one of the most common pro cesses, but little is known about the dynamics nest-building and -enlarging in social context. Furthermore, the mechanisms involved remain totally ign ored. We present here the first results of such dynamics in the context of Lasius niger's nest excavation. We find, with an artificial but standardize d method, a strong positive correlation between the number of ants and the final nest volume as well as the digging rate. Both grow almost proportiona lly to population. When the number of individuals is artificially increased (even slightly) in a nest, its dimension is systematically adjusted in the same way as initial excavation. In this process, digging acts as a negativ e feedback that controls nest enlargement. Experiments revealed that this n egative control is due directly to the volume of the nest as well as the ph ysiological or behavioral modification of ants after digging. Finally, ampl ification of activity was observed during the enlargement phase, suggesting the possible implication of self-organized processes in the volume control mechanism.