Termite air-conditioning

Termites are amazing little critters. They are tiny, even by insect standards, yet they build towers as high as 7 meters to house colonies that can consist of several million animals. They even cultivate their own food inside these termite mounts, which are constructed from a mix of soil and plant materials glued together using termite excrement and saliva. This mix becomes rock hard and protects the insects from most outside threats.

But living in a fortress without windows has its downsides, too: One challenge for the termites is getting enough fresh air into the intricate system of tunnels they inhabit. There have been various theories on how fresh air gets into the mounts but a news study published in this month’s #link:http://www.pnas.org/content/early/2015/08/25/1423242112:Proceedings of the National Academy of Sciences (PNAS)# has recorded what actually happens inside the mounts and revealed that the mounts ventilate themselves thanks solely to their ingenious design.

The team studied a number of different termite mounts in India, some of them inhabited, some abandoned. They took day and nighttime temperature readings, blew air over the mounts, covered them with tarps, used custom-designed probes and even tested suction using vacuum cleaners. In the end they concluded that the key to the ventilation was the internal structure of the mounts.

At their core, large chimneys run from the bottom, where the bulk of the colony lives, to the top. These chimneys are surrounded by thick walls but also connected to smaller tunnels and conduits. The outer walls of the mount, however, while also strong, are not air tight and allow for the exchange of gases.

When the sun shines on the termite mount during the day, the mount’s surface and thus the air inside the cavities that lie close to its surface heat up faster than the air in the chimneys, which are insulated by the thicker, inner walls.

“What you get is a convection cell,” explains L. Mahadevan, Professor of Applied Mathematics, of Organismic and Evolutionary Biology, and of Physics at Harvard University and one of the authors. “The warm air can’t move through the walls quickly enough, but it has to go somewhere, and the only possibility is for it to go down into the interior through the central chimney. At night, as the exterior cools, the airflow reverses, and it pulls the air up from the central part of the mound.”

So the air flows through the mount in one direction during the day and in the other at night, creating a natural air-conditioning system that works all by itself. Pretty smart for an animal this small.