Meeting Abstract
The subterranean nests of S. invicta fire ants are stunningly sophisticated. Nest construction is accomplished through the collective effort of multiple workers. Our laboratory experiments revealed that the workload distribution within excavating groups of S. invicta was unequal. That is, a disproportionally large amount of effort is accomplished by a few workers, while the least active workers contribute to less than 1% of the collective effort. To better understand the challenges and advantages of such a workload organization we built robotic diggers. Small groups of fully autonomous robots governed by environmental clues were set to excavate simulated cohesive soil. The collective behavior within the group was coordinated by one of two social protocols. In groups governed by the first protocol all robots contributed to excavation continuously and equally. In groups governed by the second protocol the workload was asymmetrically distributed among workers. The experiments showed that with an increase in the size of the excavating group the amount of interactions between workers within the tunnel grew and led to traffic jams. The jamming slowed excavation rates while it amplified nest excavation costs. The asymmetric workload distribution resulted in the reduction of jamming. The largest tested excavating group with asymmetric workload distribution showed on average 35% higher excavation rates at 2.2 times lower excavation costs as compared to the equal workload distribution. We hypothesize that the asymmetric workload distribution could be beneficial for task performance when the resources for the task (space in our experiments) are limited.
