Meeting Abstract
S. invicta red imported fire ants (RIFA) construct complex subterranean nests. Nest construction is a collective effort emerging from interactions of individual workers with each other and the environment. We studied the distribution of the work load in small groups of RIFA during nest construction. In laboratory experiments, groups of thirty labeled RIFA were challenged to excavate nests in transparent containers filled with simulated soil of d=0.24 mm grain size and wetness W (W =0.01 or W=0.1 by mass). The excavation process was recorded continuously over 48 hours. The video data were analyzed to determine which ants participated in the excavation process and the proportion of the workload corresponding to each individual. We found that group members did not contribute to excavation equally. Aggressive diggers performed up to 50% of the total number of group excavations, while the contribution of less active individuals was sometimes less than 1%. We used Gini coefficient, G, derived from Lorenz curve to describe the inequality of work load distribution in groups of digging RIFA. We found that the average value of G was 0.74 (maximum value of G = 1) and was not affected by soil wetness W (p=0.21). Although the contribution of individuals to excavation varied with time, G did not vary with time G (p=0.31). The high values of G suggest that aggressive diggers were present in all experiments. We posit that an asymmetry of workload distribution is an important component of the organization of nest excavation and could function to reduce tunnel crowding.
