Fungus-harvesting termites Odontotermies obesus build one– to two-meter-high fluted mounds above their subterranean nests. As the termites construct these cathedral-like, porous clay structures, they build passages within that are subsequently traveled for further construction and repair. These conduits are also thought to regulate microclimate in the nest below—but until recently, how they control temperature, moisture, and respiratory gas exchange remained unknown.
To investigate this phenomenon, Hunter King, Samuel Ocko, and Lakshminarayanan Mahadevan at Harvard University first built a highly sensitive probe to measure carbon dioxide, humidity, and temperature inside the mound—and to gather the data quickly. Termites are known to attack foreign objects often within moments. “They’ll gunk the probe up with mud, saliva, and sometimes they’ll fry themselves trying,” said Mahadevan. Probes were inserted at various locations (base, top, middle, inside) of inhabited mounds, and at different times during the day and night. The same measurements were also taken from an abandoned mound.
The researchers found that the architecture of the mound enables the structure to function like a giant lung, inhaling and exhaling once every 24-hour period. During the day, warm air travels through conduits up the sides of the mound, pushing cooler air down through more central chimneys. At night, this convection cell reverses course to keep the nest warm. The porosity of the mound allows for carbon dioxide exchange with the environment as the air moves past the exterior walls.
An understanding of termite mound ventilation could lead to more efficient management of human buildings. Mahadevan says the mound works like an engine, using temperature oscillations to do the work of moving air. “It is possible, at a reasonable scale, to use environmental fluctuations to get work out of [a structure].” He hopes engineers might be able to learn some lessons from his team’s study of mound ventilation for efficient building design, and in the meantime take advantage of the thermal gradients in existing buildings to power ventilation. He wonders, “Could it be as easy as the coordinated opening and closing of windows and doors throughout the day?” (PNAS)