Ventilation of termite mounds: new results require a new model

In 1955, Luscher proposed a ventilation mechanism for cathedral-shaped term ite mounds to exchange respiratory gases. This mechanism was generally acce pted, although it had never been tested critically. We tested this mechanis m by investigating temperatures, CO2 concentrations, and air currents in an d around two types of Macrotermes bellicosus mounds: cathedral-shaped mound s with many ridges and thin walls located in the savanna and dome-shaped mo unds without ridges and with thick wails in the forest. These two mound sha pes have two different mechanisms of ventilation, depending on the environm ental temperature. In the savanna during the day, sun heats the air in the peripheral air channels inside the ridges of the mound above the central ne st temperatures and produces a temperature gradient in the peripheral air c hannels with decreased temperatures at the top of the mound. This temperatu re gradient leads to convection currents with air rising inside the air cha nnels of the ridges to the top of the mound, meanwhile exchanging CO2. In c ontrast, in the savanna during the night and generally in the forest, the t emperatures inside the air channels are lower than those of the central nes t, and no air currents rising upward inside the air channels were detected. The CO2 concentrations in the air channels of savanna mounds at night and forest mounds in general were higher than during the day in the savanna. Th erefore, our data do not support Luscher's proposed mechanism.