Did you know...

…that Namibian termite mounds act like solar-powered air cons?

Large termite mounds created by the genus Macrotermes are common in Africa. In Namibia, such mounds created by the species Macrotermes michaelseni, can be easily seen all the way towards Etosha, as here in this image just 10 km north-west of Otjiwarongo. Within the galleries of the mounds, the termites grow a special fungus (named Termitomyces) which helps them to digest most of the cellulose of the collected litter.

There are several Macrotermes species in Namibia such as M. michaelseni, M. subhyalinus, and M. vitrialatus in the northern half of the country but with M. natalensis and its low mounds also a species stretching towards the south. A particularly well studied species is Macrotermes michaelseni, which builds the typical mounds with a conical base and a tall vertically-oriented spire. These mounds have usually sizes between 1-3 m and the spire tends to tilt slightly northward towards the sun’s average zenith. Previously, it has been assumed that the temperature circulation within the mounds is primarily driven by external wind breezes. Now, these mounds have been thoroughly examined by American scientists in the area near Otjiwarongo (Ocko et al. 2017), finding out that the internal air currents are driven by solar power. Since the mounds are located in the southern hemisphere, the northern part of the mound receives much more direct sunlight and especially during winter, may be around 5°C warmer than its south-facing surface. During the course of the day the sun-heated surface zone moves across the mound from dawn to dusk and thereby generates temperature gradients that drive the air flow. These daily temperature oscillations cause the air flow to reverse twice per day. At midday air in the hotter periphery of the mound moves upwards but inside the cooler center downwards, while at night this flow direction switches because the outer periphery cools down more quickly than the center of the mound. From this point of view and as the authors of the study conclude, the termite mounds function as an externally driven, solar-powered lung that regulates the climate of the colony.