Termite colonies

From David Attenborough's Life on Earth (p. 100):

Termites construct some of the greatest of all insect buildings. A termite fortress, walled, buttressed, and castellated, may contain ten tons of mud and stand three or four times as tall as a man. Several million inhabitants, busily running their errands within, can cause overheating and produce a foul oxygen-poor atmosphere so ventilation is of the greatest importance. Around the margins of the hill, the termites construct tall, thin-walled chimneys which stand out from the sides like ribs. No insects live inside these huge smooth-walled ducts. Their only function is ventilation. As the sun warms their walls, the air inside becomes hotter than that in the centre of the nest. It rises, drawing exhausted air from the central galleries and the deeper parts of the hill, creating a circulation. The thin, external walls of the chimneys are porous and so oxygen from the outside atmosphere diffuses in. The air, thus refreshed, rises to the top of the nest and then circulates back down other passageways. In very hot weather, the workers descend tunnels that go deep into the ground to the water table. Each returns carrying a crop full of water with which it wets the walls of the main part of the nest. The heat evaporates the water and this also lowers the temperature. By such devices, the worker termites manage to keep a very even temperature inside the nest.