Data from: Who needs 'lazy' workers? Inactive workers act as a 'reserve' labor force replacing active workers, but inactive workers are not replaced when they are removed

Social insect colonies are highly successful, self-organized complex systems. Surprisingly however, most social insect colonies contain large numbers of highly inactive workers. Although this may seem inefficient, it may be that inactive workers actually contribute to colony function. Indeed, the most commonly proposed explanation for inactive workers is that they form a ‘reserve’ labor force that becomes active when needed, thus helping mitigate the effects of colony workload fluctuations or worker loss. Thus, it may be that inactive workers facilitate colony flexibility and resilience. However, this idea has not been empirically confirmed. Here we test whether colonies of Temnothorax rugatulus ants replace highly active (spending large proportions of time on specific tasks) or highly inactive (spending large proportions of time completely immobile) workers when they are experimentally removed. We show that colonies maintained pre-removal activity levels even after active workers were removed, and that previously inactive workers became active subsequent to the removal of active workers. Conversely, when inactive workers were removed, inactivity levels decreased and remained lower post-removal. Thus, colonies seem to have mechanisms for maintaining a certain number of active workers, but not a set number of inactive workers. The rapid replacement (within 1 week) of active workers suggests that the tasks they perform, mainly foraging and brood care, are necessary for colony function on short timescales. Conversely, the lack of replacement of inactive workers even 2 weeks after their removal suggests that any potential functions they have, including being a ‘reserve’, are less important, or auxiliary, and do not need immediate recovery. Thus, inactive workers act as a reserve labor force and may still play a role as food stores for the colony, but a role in facilitating colony-wide communication is unlikely. Our results are consistent with the often cited, but never yet empirically supported hypothesis that inactive workers act as a pool of ‘reserve’ labor that may allow colonies to quickly take advantage of novel resources and to mitigate worker loss.

群居昆虫群落是一类高度成功的自组织复杂系统。不过令人意外的是，绝大多数群居昆虫群落中都存在大量高度不活跃的工蚁。尽管这看似低效，但实际上不活跃的工蚁或许对群落功能有着贡献。目前针对不活跃工蚁最主流的解释为：它们构成了一支“储备”劳动力，在有需求时便可被激活，从而帮助缓解群落工作负荷波动或工蚁损失带来的影响。由此可见，不活跃工蚁或许能提升群落的灵活性与恢复力。但这一假说尚未得到实验验证。本研究通过实验移除特定工蚁，以此检验红凹细胸蚁（Temnothorax rugatulus）群落是否会补充被移除的高活跃度（即大量时间用于特定任务）或低活跃度（即大量时间完全静止）工蚁。实验结果显示：即便移除了高活跃度工蚁，群落仍能维持移除前的活动水平，且此前不活跃的工蚁会在高活跃度工蚁被移除后转为活跃状态。反之，当移除不活跃工蚁后，群落的不活跃水平会下降，并在移除后维持在较低水平。由此可见，群落似乎拥有维持固定数量活跃工蚁的机制，但并不维持固定数量的不活跃工蚁。高活跃度工蚁会在1周内得到快速补充，这表明它们所承担的觅食、育幼等主要任务，在短时间尺度上对群落功能而言是不可或缺的。反之，即便在移除不活跃工蚁两周后，群落也未对其进行补充，这说明不活跃工蚁的任何潜在功能（包括作为储备劳动力）都相对次要或仅具辅助作用，无需立刻得到补充。综上，不活跃工蚁虽可作为储备劳动力，且可能承担群落食物储存的功能，但不太可能在群落整体通讯中发挥作用。本研究结果与长期被引用却从未得到实验验证的假说相符：即不活跃工蚁构成了“储备”劳动力库，可帮助群落快速利用新型资源，并缓解工蚁损失带来的影响。