Across the forests and prairies of Asia, and vast savannahs of Africa, live secret societies of architects. They are masters of construction, their sophisticated and innovative green-energy designs perfectly capturing the current trend for environmentally friendly construction. And yet these architects don’t like to share their secrets: exactly how – and why – they build their towering constructions has until recently remained somewhat mysterious.
Who are these master builders? They are the mound-building termites. Although they resemble whitish brown grains of rice with big heads and hedge-trimmers for mouthparts, these insects are ecological heavy hitters. Termites control a significant portion of the flows of carbon and water through dry savannah ecosystems, says Scott Turner, a professor of biology at the State University of New York. “They can build anywhere there is grass and water.”
Scientists have wondered why termites build mounds that can be 30ft high
Part of the reason termite mounds are the focus of so much scientific attention is that the insects don’t really live inside them. They choose instead to build their nests – which can be home to thousands or even millions of individuals – in the ground below the mound. In fact, they only travel into the mounds to repair them and defend the city below from invading ant armies and other threats.
For decades, scientists have wondered why termites go to all the trouble of building mounds that, for some species, can be 30ft (9.1m) high. There have been hypotheses, but in recent years, new science has debunked some of them. Engineers, biologists, and architects that study termites are now developing a new theory to explain the spectacular mounds – and their findings may help revolutionise the way we construct our own buildings.
Like us, termites build an environment that suits them rather than adapting to their environment. They sometimes live in arid regions that would dry out their bodies, for instance: their mounds help counteract the problem by maintaining an environment that is cool and humid.
The humidity isn’t just important to the termites. The termites make a living farming a fungus (Termitomyces) on structures known as fungus cones. The fungus helps breakdown dead plant and woody material into more digestible and nutritious food for the termites, and they in turn help maintain the environment for the fungus. It’s a mutually beneficial arrangement.
The mound is like a physiological extension of the termites themselves: a giant lung
There’s a lot of hustle and bustle in the termite nest, and both the fungi and the termites produce a lot of carbon dioxide. The problem, says Hunter King, a postdoctoral student at Harvard University, is that eventually they need to get rid of it.
Though there has been previous research investigating how carbon dioxide is swapped for oxygen in the mound, King says that in those studies, nobody measured the flows directly.
That’s why King, along with colleague Samuel Ocko from the Massachusetts Institute of Technology and supervisor Lakshminarayanan Mahadevan from Harvard University designed a study that would allow them to directly measure temperature, carbon dioxide and humidity in the mounds of Odontotermes obesus termites.
Turns out, it’s tricky to take gas measurements within a termite mound.
It’s a lot of work to build a mound, and so naturally, termites go to great lengths to make sure it has solid defences. It’s that defence system – like a state of the art burglar alarm – that makes measurements inside so difficult to take.
“You have about five minutes before they attack,” says Hunter, who with Ocko designed a probe sensitive enough to record the information they needed before the termite repair team came and smeared it with sticky mud blobs. Not only did the probe need to record data quickly, it also needed to be affordable enough to replace and repair after the termites gunked it up many, many times over.
Though some sensors were lost, the team gathered the information they needed. What they found dispelled previously held ideas that the mound functioned like a kind of passive air conditioner. In fact, it appears that one of the most important functions of the mound is gas exchange. The mound is like a physiological extension of the termites themselves: a giant lung.
The nest is actually constructed to prevent the kind of large air flows through it
King and the team found that the architecture of the mound inhales and exhales over a 24-hour period. During the day, the outer tunnels of the mound are heated more rapidly than the deeper tunnels and chimneys, pushing air up the outside and down the middle. This creates a circular current that reverses at night as the outer walls lose heat more quickly. As the air flows through the mound, carbon dioxide is flushed outside through tiny holes in the mounds exterior walls, and oxygen enters the mound the same way.
The termites are using the natural daily temperature cycles to do the work of ventilating the mound for them – essentially creating a type of engine that requires no energy input from the termites themselves. This was one of the most inspiring findings of the project for King, who says that it appears one of the primary functions of the mound is to facilitate the exchange of carbon dioxide and oxygen, as opposed to regulating temperature.
This is a conclusion that fits with Scott Turner’s previous work, says King. Turner discovered that in the termite species Macrotermes michaelseni – found throughout most of Southern Africa – the mounds and nest are two very distinct air spaces. “The nest is actually constructed to prevent the kind of large air flows through it. It makes the air safer in the underground nest,” says Turner. So previous theories that the mound was designed primarily to control nest temperature are not quite right.
King has just returned from Africa, where his probes battled the termites in the mounds of the species Turner studies. His data remains to be explored, but he suspects that his new results may confirm the lung theory in another species. As for whether this newly discovered engineering feat might have human applications, “I’m hopeful that the thing we’ve described is useful to somebody,” says King.
In the meantime, Rupert Soar, an engineer and professor at Nottingham Trent University, UK, and one of King’s collaborators, says the study provides a wealth of areas to build from. “[The mound] is losing heat far faster into space at night than it is gaining during the day from the sun beating down on it. I just thought that was amazing.”
If we could do that with buildings, we’ve really cracked it – we’ve done something that people haven’t been able to do for generations
Soar is interested in the role that the tiny holes in the exterior walls play in dispersing carbon dioxide. He explains that right now, when we seek to control the internal environments of our office towers, homes and shopping malls, we need to use powered fans, pumps and other ventilation systems to maintain the internal environment.
“The termites have created this specially structured skin that allows the free exchange of carbon dioxide and oxygen, but conserves this temperature and moisture regime that they need inside. If we could do that with buildings, we’ve really cracked it – we’ve done something that people haven’t been able to do for generations,” says Soar.
Imagine not having to pay the energy bills for those whirring fans and chugging ventilation systems! It’s insights like these that continue to inspire Soar to look to termites for creative engineering solutions.
As of late his work is focused on the fungus cone, a structure resembling brain coral located deep within the nest. The cone is made up of the comb-like structures on which termites garden the fungus. In collaboration with Turner, Soar discovered that as the fungus grows, its surface becomes covered with a “hyphal mat” of tiny hair-like cilia. “What we’ve discovered is that this fungus cone has an ability to clamp the humidity levels inside the termite mound, at a very specific level.”
Soar says that if we are able to understand how this mechanism works, people might develop materials that could be used to control and regulate excess humidity within a building. It could be another technology that further reduces the energy our buildings need to suck from the grid.
It could be a technology that reduces the energy our buildings need to suck from the grid
But the real breakthrough, says Soar, would be in understanding how the mounds are built in the first place.
With hundreds of thousands of termites running about, how do they coordinate their efforts to build mounds at a scale so much larger than themselves? Is there a tiny sergeant barking orders that only termites can hear?
It turns out there is no head engineer or master architect directing the masses, says Judith Korb, a professor at the University of Regensburg, Germany. She studies the evolution of cooperation in termites and other species. “What you really have is self organisation.”
What this means, says Korb, is that each individual is pre-programmed to carry out a certain behaviour. She says mound-building looks like this: a termite will grab one soil particle, mix it with water and saliva and cement it in place. The next termite will come along and put their soil blob down next to the one previous, and this continues until eventually a wall is built. However, soon there are too many termites walking around with soil blobs, and this results in a termite traffic jam.
At that point, termites give up and just drop their blobs where they are. Then another termite blob-drops next to them, beginning another structure. Eventually walls and tunnels connect, and at some point, a mound almost magically appears.
The mechanism by which this building chaos eventually becomes a magnificent mound is not well understood. Some have wondered if termites emit a building pheromone that helps them organise.
Perhaps termites are not just master builders, but master plumbers too
But Soar thinks the answer might be simpler than that. He wonders if termites have a genetically ingrained sensitivity to moisture that helps them do everything from building to maintaining the mound. For example, he says that when building, termites will only lay down their soil particle next to another that has a very specific moisture content. Otherwise, they move on.
Could moisture act like a central computer system, providing termites with information about everything from where to lay a soil blob when building, to how stuffy the mound is, and to how much ventilation is going through it? Imagine a scenario where a termite senses the mound is too dry, and goes to look for a hole to repair, or a wall to thicken.
Soar says it’s very early days in the development of his theory, but it’s exciting to think that something as simple as moisture could have repercussions throughout the mound. Perhaps termites are not just master builders, but master plumbers too.
Regardless, it’s certain termites have much more to teach us – particularly as we continue our efforts to better harness the power of the sun and wind to construct the buildings of the future.