Building Castles on the Ground: Conversations Between Ecologists and Engineers

The architectural feats of termites and their farming capabilities have been admired by biologists, engineers and architects and have inspired writers including early natural historians. South India is endowed with termite mud castles; their seeming impregnability threw up intellectual challenges, initiating conversations between biologists and engineers. The biologists were interested in how termites kept their farmed basidiomycete fungus free from parasites and discovered experimentally that termites can sniff out parasitic ascomycete fungi, proceed to anoint them with broad-spectrum fungicides and bury them resulting in mortality-yielding anoxia. High levels of humidity and carbon dioxide inside soil nests are conducive to the growth of parasitic fungi whose density is likely actively supressed by eradication of incipient foci of parasite growth by the termite farmers. The engineers were interested in how the mound acquired its strength, stability and longevity while allowing gas exchange. They discovered that the safety factor of termite mounds is very high, that termite-manipulated soil achieves great strength and weathering resistance, that termites manipulate the water content of soil between its plastic and liquid limits and that mounds have a more porous exterior shell and a less porous core. Dialogues between biologists and engineers have enabled insights into the bio-engineering aspects of animal-built architecture. The natural biological constraints of the termite builders (e.g. size, load-carrying ability in relation to particle grain size, caste) and available material (red soil containing organic matter) in the presence of water have been realistically incorporated into modelling the greenhouses that harbour termites and their crops.