Termites of the genus Macrotermes are renowned for the large accessory mounds they build. The mound is not the colony’s habitation, but an organ of gas exchange, built upwards through the surface boundary layer so that energy in wind may be captured to power ventilation of the subterranean nest. The mound is built by the upward transport of soil by worker termites from deep horizons, which offsets the roughly cubic meter of soil that erodes from the mound each year. This makes the Macrotermes mound a dynamic structure, which confers upon the mound its most remarkable property: its ability to act as an organ of homeostasis of the nest atmosphere. In the face of varying metabolic demands and environmental conditions, the composition of the atmosphere of Macrotermes nests appears to be actively regulated. This can only come about if the mound’s architecture can be adjusted to always bring wind-driven gas exchange into conformity with respiratory gas exchange of the colony. Such emergent homeostasis probably arises through distributions of respiratory gases within the mound acting as a “gaseous template” that guides the termites’ collective transport of soil, and hence the mound’s architecture. This emergence of extended physiology offers a general model for the emergence of physiology at multiple scales of organization.