How termite mounds function to facilitate climate control is still only
partially understood. Recent experimental evidence in the mounds of
a single species, the south Asian termite Odontotermes obesus,
suggests that the daily oscillations of radiant heating associated with
diurnal insolation patterns drive convective flow within them. How
general this mechanism is remains unknown. To probe this, we
consider the mounds of the African termite Macrotermes michaelseni,
which thrives in a very different environment. By directly measuring air
velocities and temperatures within the mound, we see that the overall
mechanisms and patterns involved are similar to that in the south
Asian species. However, there are also some notable differences
between the physiology of these mounds associated with the
temporal variations in radiant heating patterns and CO2 dynamics.
Because of the difference between direct radiant heating driven by
the position of the sun in African conditions, and the more shaded
south Asian environments, we see changes in the convective flows
in the two types of mounds. Furthermore, we also see that the
south Asian mounds show a significant overturning of stratified gases,
once a day, while the African mounds have a relatively uniform
concentration of CO2. Overall, our observations show that despite
these differences, termite architectures can harness periodic solar
heating to drive ventilation inside them in very different environments,
functioning as an external lung, with clear implications for human
engineering.