As builders go, termites don’t have many tools at their disposal — just their bodies, soil, and saliva. For guidance they have nothing to go on save variations in wind speed and direction and fluctuations in temperature as the sun rises and sets.
Despite such limitations, the insects have managed to develop structures that are efficiently ventilated, a challenge that’s still a struggle for human builders.
Led by L. Mahadevan, Lola England de Valpine Professor of Applied Mathematics, of Organismic and Evolutionary Biology, and of Physics, a team of researchers that included postdoctoral fellow Hunter King and MIT grad student Samuel Ocko has for the first time described in detail how termite mounds are ventilated. The study, described in an Aug. 31 paper in the Proceedings of the National Academy of Sciences, reveals that the structures act similarly to a lung, inhaling and exhaling once a day as they are heated and cooled.
“The direct measurements essentially overthrow the conventional wisdom of the field,” said Mahadevan. “The classic theory was that if you have wind blowing over the mounds, that changes the pressure, and can lead to suction of CO2 from the interior … but that was never directly measured.
“We measured wind velocity and direction inside the mounds at different locations. We measured temperature, CO2 concentrations … and found that temperature oscillations associated with day and night can be used to drive ventilation in a manner not dissimilar to a lung. So the mound ‘breathes’ once a day, so to speak.”
Mahadevan first got interested in termite mounds more than five years ago, during a visit to the National Centre for Biological Sciences in India. He was surprised to learn that many of the ideas about how the mounds functioned hadn’t been rigorously tested.
Working with Scott Turner, a professor at SUNY College of Environmental Science and Forestry and the author of a book that examines animal-built structures, Mahadevan, King, and Ocko assembled a plan aimed at finding more definitive answers.
“It occurred to us that the internal flow profiles predicted by different potential mechanisms qualitatively disagree with each other,” King said. “By measuring them directly, we could easily identify the right one. The hard part was figuring out how to sensitively measure these small flows in a confined space defended by glue-and-mud-excreting termites.”