The Role of Anchor-Tipped Larval Hairs in the Organization of Ant Colonies

The spatial organization within a social insect colony is a key component of colony life. It influences individual interaction rates, resource distribution, and division of labor within the nest. Yet studies of social insect behavior are most often carried out in artificial constructions, which may change worker behavior and colony organization. We observed how workers of the ant Pheidole rhea organized brood in nests with deep chambers and textured walls that were designed to mimic their natural constructions more closely. Instead of clumping larvae into piles on the chamber floor, workers suspended fourth-instar larvae from the vertical walls and ceiling of each chamber while young larvae and pupae were clumped at the base. Fourth-instar larvae possess five rows of anchor-tipped hairs on their dorsal side, and we predicted that these hairs functioned to attach larvae to the nest walls. We gave larvae “haircuts,” where only the anchor-tipped hairs were removed, and then tested their ability to adhere to a textured surface raised to an angle of 90° and then 120° with respect to the horizontal plane. Larvae whose hairs had been clipped came unattached in almost all trials, while larvae whose hairs remained intact stayed attached. This confirmed that anchor-tipped hairs functioned to attach larvae to the walls of the nest. The presence of anchor-tipped hairs is widespread and has been documented in at least 22 genera from the ant subfamily Myrmicinae, including species that occur in a variety of environments and represent a broad range of nesting habits. Based on our results, it is likely that many species exhibit this larval hanging behavior, and this could impact colony characteristics such as spatial organization and the care of developing larvae by nurse workers.社会性昆虫种群的空间组织结构是种群生存的核心组成部分，其可影响巢内个体间的互动频率、资源分配模式与劳动分工体系。然而现有社会性昆虫行为研究大多依托人工构筑的巢箱开展，此类人工环境可能会改变工蚁的行为模式与种群的空间组织结构。本研究以雷氏大头蚁（Pheidole rhea）为研究对象，观察其工蚁在具有深巢室与纹理壁面的模拟天然筑巢环境的巢箱中，如何整理育幼个体。工蚁并未将幼虫堆放在巢室地面，而是将四龄幼虫悬挂于各巢室的垂直壁面与顶部；与此同时，低龄幼虫与蛹则被聚集于巢室底部。四龄幼虫的背部生有五排带有锚状尖端的刚毛，研究团队推测此类刚毛可帮助幼虫附着于巢壁之上。为此，我们对幼虫实施“修毛处理”——仅移除其锚状尖端的刚毛，随后测试幼虫在与水平面呈90°、再调整至120°的纹理表面上的附着能力。试验结果显示，刚毛被剪除的幼虫几乎全部脱落，而保留完整刚毛的幼虫则始终附着于表面。这证实了锚状尖端刚毛确实具备帮助幼虫附着于巢壁的功能。带有锚状尖端刚毛的特征分布广泛，目前已在蚁科切叶蚁亚科（Myrmicinae）的至少22个属中被记录，涵盖了多种生存环境与筑巢习性的类群。基于本研究结果，诸多蚁类物种或均存在此类幼虫悬挂行为，而该行为可能会对种群的空间组织结构、保育工蚁对发育中幼虫的抚育等种群特征产生影响。