Mound-building macrotermites construct vertical mounds out of soil, saliva, and dung, with some mounds in Africa measuring up to several meters high. While mound structure can vary among termite species, the mounds generally resemble chimneys, with some mounds having large vents while others lack large openings but have porous walls. Inside these mounds, worker termites can dig a complex array of tunnels of various sizes. The termites themselves live in nests below ground in colonies that can contain up to a million individuals.
The most recent published research on termite mounds suggests that they function much like mammalian lungs and act as accessory organs for gas exchange in the underground nests. It was previously thought that termite mounds functioned to continuously maintain the nest’s internal temperature within a narrow range in the face of extreme outside temperature fluctuations, but research on the mound-building termite Macrotermes michaelseni is expanding our understanding of mound function. During the day, changes in internal nest temperature are less extreme than changes in outside temperature, but over the course of a year, nest temperature does vary and closely follows the temperature of the surrounding soil. The soil has a large thermal capacity, meaning it can absorb or lose large amounts of heat energy before experiencing any changes in temperature. In a way, the soil around the termite nest acts as a “buffer” against daily changes in outside temperature.
Termite researchers are actively studying mounds to understand precisely how mound structure facilitates gas exchange in the underground colony. It appears that a mound’s structure enables it to harness wind energy from the unsteady, dynamic airflows outside the mound. Rather than generating continuous airflow through the mound, this wind energy likely promotes mixing between air in the mound and air in the nest, ultimately facilitating gas exchange in the nest. This growing understanding of macrotermite mound structure and function could inspire new biomimetic technologies in energy-saving climate control systems.
For more detailed information on how a termite mound can function like a lung, check out this video.
“The macrotermitine termites build some of the most spectacular animal-built structures on the planet. Some, like the mound of Macrotermes michaelseni…are dominant landscape features over much of southern Africa. These termites control a significant portion of the flows of carbon and water through arid savanna ecosystems. These remarkable structures are not the residence for the colony–very few termites actually are found in them. Rather, they are accessory organs of gas exchange, which serve the respiratory needs of the subterranean colony, located about a meter or two below the mound…Functionally, these mounds are devices for capturing wind energy to power active ventilation of the nest. They are adaptive structures, continually molded by the termites to maintain the nest atmosphere. This ability confers on the colony emergent homeostasis, the regulation of the nest environment by the collective activities of the inhabitants.” (Turner 2000)
“As it is in lungs, the colony’s respiratory function is dominated by a mixed-phase regime that is sandwiched between the subterranean structures (where natural convection dominates), and the upper parts and peripheral air spaces of the mound (where wind-driven forced convection dominates). By our best estimates, this mixed natural/forced convection regime occupies the lower parts of the chimney and the deeper parts of the mound reticulum .” (Turner and Soar 2008:222)
“…so-called pendelluft ventilation (literally, air pendulum) enhances gas exchange across the mixed-regime region of lungs through weakly-driven bulk flows of air between alveolar ducts and between the fine bronchi (Figure 7, [17, 18]). We believe there is a pendelluft in termite mounds as well, driven by an interaction between buoyant forces generated by the colony, slow transients in turbulent wind energy that penetrate to the lower chimney and subterranean tunnels and the rapid transients that drive flows in the superficial tunnels…The end result of these complicated interactions is a pendelluft that drives slow quasi-tidal air movements in the chimney and lower parts of the mound interior, enhancing exchange between the nest and mound .” (Turner and Soar 2008:222-223)
“In most building designs, walls are erected as barriers to isolate spaces: internal spaces from the outside world,internal spaces from one another and so forth. Yet spaces, if they are to be occupied and used, cannot be isolated. Resolving this paradox is what forces building designs to include infrastructure—windows, fans, ducts, air conditioning, heating etc—all essentially to undo what the erection of the walls did in the first place. In short, the paradox forces building design toward what we call the “building-as-machine” paradigm (BAM).
Living systems, which also are avid space-creators, resolve the paradox in a different way: by erecting walls that are not barriers but adaptive interfaces, where fluxes of matter and energy across the wall are not blocked but are managed by the wall itself [28, 29]. This is illustrated dramatically in the complex architecture of the interface that termites build—the mound—to manage the environment in their collectively constructed space—the nest .” (Turner and Soar 2008:225)