School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA School of Biology, Georgia Institute of Technology, Atlanta, GA 30332, USA
J Exp Biol. 2014 Jun 15;217(Pt 12):2089-100. doi: 10.1242/jeb.093021.
To overcome obstacles and survive harsh environments, fire ants link their bodies together to form self-assemblages such as rafts, bridges and bivouacs. Such structures are examples of self-assembling and self-healing materials, as ants can quickly create and break links with one another in response to changes in their environment. Because ants are opaque, the arrangement of the ants within these three-dimensional networks was previously unknown. In this experimental study, we applied micro-scale computed tomography, or micro-CT, to visualize the connectivity, arrangement and orientation of ants within an assemblage. We identified active and geometric mechanisms that ants use to obtain favorable packing properties with respect to well-studied packing of inert objects such as cylinders. Ants use their legs to push against their neighbors, doubling their spacing relative to random packing of cylinders. These legs also permit active control of their orientation, an ability ants use to arrange themselves perpendicularly rather than in parallel. Lastly, we found an important role of ant polymorphism in promoting self-aggregation: a large distribution of ant sizes permits small ants to fit between the legs of larger ants, a phenomenon that increases the number of average connections per ant. These combined mechanisms lead to low packing fraction and high connectivity, which increase raft buoyancy and strength during flash floods.
为了克服障碍和在恶劣环境中生存，火蚁将它们的身体连接在一起，形成自组装体，如筏子、桥梁和营地。这些结构是自组装和自修复材料的例子，因为蚂蚁可以根据环境的变化快速地相互创建和断开连接。由于蚂蚁是不透明的，因此这些三维网络中蚂蚁的排列方式以前是未知的。在这项实验研究中，我们应用微尺度计算机断层扫描（micro-CT）来可视化组装体中蚂蚁的连通性、排列和方向。我们确定了蚂蚁用来获得有利的堆积特性的主动和几何机制，这些特性与惰性物体（如圆柱体）的良好堆积研究有关。蚂蚁用它们的腿推挤它们的邻居，使它们之间的间隔相对于圆柱体的随机堆积增加一倍。这些腿还允许它们主动控制自己的方向，蚂蚁利用这种能力将自己垂直排列，而不是平行排列。最后，我们发现蚂蚁多态性在促进自聚集方面起着重要作用：蚂蚁大小的广泛分布允许小蚂蚁在大蚂蚁的腿之间穿梭，这种现象增加了每只蚂蚁的平均连接数。这些综合机制导致了低堆积分数和高连通性，从而在洪水期间增加了筏子的浮力和强度。
