M. Smithii nests in Puerto Rico, Costa Rica, and Trinidad

M. Smithii nests in Puerto Rico, Costa Rica, and Trinidad have a single entrance, though the close proximity to other nests in high colony-density areas may give the illusion of multiple entrances. M. Smithii nests consist of a mound excavated around an entrance roughly 1.2 mm in diameter. This leads to a vertical tunnel opening into the garden chamber at a depth of approximately 12.5 mm. M. Smithii maintain narrow tunnels (diameter of 1.3 mm) which do not allow two ants to pass each other in the tunnel (head size is approximately 0.7 mm for workers and 0.9 mm for queens). The tunnels also have a number of slightly larger sections (approximately 3.6 mm diameter) which would allow passing while also facilitating information exchange. Narrow tunnels are presumably easier (energetically cheaper) to construct and may also aide in leveling the humidity or temperature of the colony or preventing predatory intrusions.