Large body sizes have evolved structures to facilitate resource transport. Like unitary organisms, social insect colonies must transport information and resources. Colonies with more individuals may experience transport challenges similar to large-bodied organisms. In ant colonies, transport occurs in the nest, which may consist of structures that facilitate movement. We examine three attributes of nests that might have evolved to mitigate transport challenges related to colony size: (1) subdivision-nests of species with large colonies are more subdivided to reduce crowd viscosity; (2) branching-nest tunnels increase branching in species with large colonies to reduce travel distances; and (3) shortcuts-nests of species with large colonies have cross-linking tunnels to connect distant parts of the nest and create alternative routes. We test these hypotheses by comparing nest structures of species with different colony sizes in phylogenetically controlled meta-analyses. Our findings support the hypothesis that nest subdivision and branching evolved to mitigate transport challenges related to colony size. Nests of species with large colonies contain more chambers and branching tunnels. The similarity in how ant nests and bodies of unitary organisms have evolved in response to increasing size suggests common solutions across taxa and levels of biological organization.

Large body sizes have evolved structures to facilitate resource transport. Like unitary organisms, social insect colonies must transport information and resources, and colonies with more individuals may experience transport challenges similar to large-bodied organisms. In ant colonies, transport occurs in the nest, which may consist of structures that facilitate movement. We examine three attributes of nest structures that could mitigate transport challenges related to colony size: (1) subdivision - nests of species with large colonies are more subdivided to reduce viscosity of large crowds; (2) branching - nest tunnels increase branching in species with large colonies to reduce travel distances; and (3) short-cuts – nests of species with large colonies have cross-linking tunnels to connect distant parts of the nest and create alternative routes. We test these hypotheses by comparing nest structures of species with different colony sizes in phylogenetically controlled meta-analyses. Our findings support the subdivision and branching hypotheses. The nests of species with large colonies contain more, but not larger, chambers and reduce travel distances by increasing branching frequency. The similarity in how ant nests and the bodies of unitary organisms respond to increasing size suggests structural solutions that are common across levels of biological organization.