Ventilation of termite mounds: New results require a new model

Abstract

In 1955, Luscher proposed a ventilation mechanism for cathedral-shaped termite mounds to exchange respiratory gases. This mechanism was generally accepted, although it had never been tested critically. We tested this mechanism by investigating temperatures, CO2 concentrations, and air currents in and around two types of Macrotermes bellicosus mounds: Cathedral-shaped mounds with many ridges and thin walls located in the savanna and dome-shaped mounds without ridges and with thick walls in the forest. These two mound shapes have two different mechanisms of ventilation, depending on the environmental 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 nest temperatures and produces a temperature gradient in the peripheral air channels with decreased temperatures at the top of the mound. This temperature gradient leads to convection currents with air rising inside the air channels of the ridges to the top of the mound, meanwhile exchanging CO2. In contrast, in the savanna during the night and generally in the forest, the temperatures inside the air channels are lower than those of the central nest, 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. Therefore, our data do not support Luscher's proposed mechanism.