Why termites build such enormous skyscrapers

Why termites build such enormous skyscrapers

There is a new theory to explain why termites build such tall mounds – and it suggests architects could take inspiration from the tiny insects

  • By Niki Wilson

10 December 2015

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.


Collective Mind in the Mound: How Do Termites Build Their Huge Structures?

Termites move a fourth of a metric ton of dirt to build mounds that can reach 17 feet (5 meters) and higher.

PUBLISHED August 1, 2014

For the past 26 years, J. Scott Turner has filled termite mounds with propane, scanned them with lasers, and stuffed them with plaster. He has fed microscopic beads to termites, given the insects fluorescent green water, and even tried to turn termite behavior into a video game.

A professor of animal physiology at the SUNY College of Environmental Science and Forestry in Syracuse, this rangy intellectual MacGyver does it all in search of clues to a biological mystery: How do tiny termites build such spectacular structures?

A single termite can be barely bigger than the moon of a fingernail, its semi-transparent exoskeleton as vulnerable to sunlight as to being crushed by a child in flip-flops. But in groups of a million or two, termites are formidable architects, building mounds that can reach 17 feet (5 meters) and higher. The 33 pounds (15 kilograms) or so of termites in a typical mound will, in an average year, move a fourth of a metric ton (about 550 pounds) of soil and several tons of water.

The termites also “farm” a symbiotic fungus that occupies eight times more of the nest than the insects do. And some termites eat as much grass each year as an 880-pound (400-kilogram) cow.

Like ants, bees, and other social insects, termites live in societies where the collective power of the colony far outstrips that of the individual. Being part of a super-organism gives the tiny termite superpowers. But a termite mound is like a construction site without a foreman—no one termite is in charge of the project. Is there a “collective plan” encoded in the collective mind of the colony? That question has obsessed Turner for years.

In addition to experimenting in the mounds, Turner designs computer simulations to explore deeper patterns in termite behavior. It wouldn’t be wrong to say he’s been searching for the psyche of the super-organism, but it wouldn’t fully get at the richness of all of the other things he’s noticed along the way—including clues to how humans might build more energy-efficient buildings, how we might design robots to build on places like Mars, and even peculiar termite behaviors that might help us understand how our own brains work.

Termites communicate with each other using touch and vibrations.

Photograph by Mark W Moffett, National Geographic

Always Ready to Rebuild

Turner pursues his fieldwork amid the semiarid savannas of northern Namibia, on a government-owned research station named Omatjenne—the word for lightning in the local Herero language. Sure enough, on an afternoon tour of the farm, the horizon is loaded with fat, dark clouds that are soon gashed by electricity.

The life of the termite is a race against rain, Turner says. Termite mounds can take four to five years to build, but a really heavy downpour might cause a third of the mounds to collapse. So termites are always scurrying to rebuild their mounds as fast as the weather erodes them.

To demonstrate the rebuilding process, Turner uses an auger, a tool that looks like a big corkscrew, to cut into the rock-hard surface of a mound. As he pulls a six-inch (15-centimeter) plug of dirt from the side, termites pour out of the hole. Soldiers fan out with their pinching mandibles ready for battle, and workers with mouths full of dirt run to plug the hole. How do they know there’s a hole in the mound?

Termites are “novelty detectors,” attuned to excitement and always on alert, says Turner. (When there isn’t external stimulation, termites sometimes stand in little clusters, massaging each other’s antennae.) Experiments in Turner’s lab suggest they respond to slight air movements and changes in humidity and concentrations of gases like carbon dioxide.

At the first sign of a disturbance, a termite runs to communicate the news with touch and vibrations. Roused, masses of termites fill their mouths with dirt and head toward the source of the problem. The commotion attracts more termites with more dirt, and within an hour or so the hole is patched.

Scott Turner peers into a plaster cast of a termite mound to ponder its architecture.

Photograph by Mark W. Moffett, National Geographic

Peering Inside

The only way to get a glimpse of the termite super-organism in action is to rip the side off a mound. And so one morning Turner, along with entomologist Eugene Marais of the National Museum of Namibia, takes a backhoe to the test fields. With a single swoop, the backhoe removes the top of a mound and then precisely dismantles the rest, like pulling the walls off a dollhouse.

The termites are not happy that their walls have suddenly disappeared, and they swarm frantically around the exposed structure. Marais dislodges a chunk of dense soil about the size of a squashed soccer ball—the queen’s chamber.

After repeated blows of a hand pick, the capsule breaks open suddenly, revealing a saucer about five inches (almost 13 centimeters) across containing the queen. Her sweating body is swollen to the size of a human finger. A coterie of workers carries the eggs she produces—at the staggering rate of one every three seconds—to nearby nurseries, while others feed and clean her.

The queen herself, once a relatively normal size, retains her original legs, but they are now nearly useless. Her pale body pulsates, the caramel-colored fats and liquids inside swirling under her skin.

The title “queen” leads people to imagine that she is in charge of the mound, but this is a misconception. “The queen is not in charge,” says Marais. “She’s really a slave.” The queen is the epitome of the super-organism: one for all and all for one. She is a captive ovary, producing hundreds of millions of eggs over her life span of up to 15 years to populate the mound.

Termites rebuild their mounds with mouthfuls of dirt when they’re damaged or the weather erodes them.

Photograph by Mark W. Moffett, National Geographic

Farming Fungus

Below the queen’s chamber lies the super-organism’s largest organ: the fungus garden. In a symbiotic relationship dating back millions of years, the termites exit the mound through long foraging tunnels and return with their “intestines full of chewed grass and wood, which they defecate upon their return, and other workers assemble these ‘pseudo-feces’ into several mazelike fungus combs,” Turner explains.

The termites then seed the comb with spores of fungus, which sprout and dissolve the tough cellulose into a high-energy mixture of partially digested wood and grass. For the termites, the fungus functions as a sort of external stomach, but the fungus gets the better deal. Ensconced in elaborate termite-built combs and constantly tended, the fungus receives multiple benefits, including food, water, shelter, and protection.

In fact, the deal is so lopsided that it calls into question just who’s in charge of the relationship. Collectively, the colony’s fungus accounts for nearly 85 percent of the total metabolism inside the mound, and Turner speculates that the fungus may send chemical signals to the termites that influence—control?—the way they build the mound. “I like to tell people that this may not be a termite-built structure,” he says. “It may actually be a fungus-built structure.”

The collective power of the termite colony far outstrips that of the individual.

Photograph by Mark W. Moffett, National Geographic

Living Quarters

Which brings us to the most extraordinary organ: the mound itself. Contrary to common notions, termite mounds are not high-rise residence halls. Rather, they are “accessory organs of gas exchange,” in Turner’s words, designed to serve the respiratory needs of the subterranean colony located several feet (a meter or two) below the mound.

For many years, researchers looked at termite mounds and supposed that the spires worked like chimneys, drawing hot air up and out. But Turner discovered that mounds function more like lungs, inhaling and exhaling through walls that appear impenetrable but are actually quite porous.

Inside the mound, a series of bubble-like chambers connected to branching passages absorb changes in outside pressure or wind and pass them through the mound. To regulate the mix of gases and maintain a stable nest environment, the termites are forever remodeling the mound in response to changing conditions.

“A termite mound is like a living thing,” says Turner, “dynamic and constantly maintained.”

The queen (top right) produces hundreds of millions of eggs over her life span of up to 15 years to populate the mound.

Photograph by Mark W. Moffett, National Geographic

Wet Kisses

While studying termite building behavior, Turner noticed that his subjects seemed to be kissing each other, mouth to mouth, after a complicated ritual that included grooming and begging. Curious, he added fluorescent green dye to their water and discovered that all this “kissing” was actually a bucket brigade, transferring large amounts of water across the mound. A termite can drink half its own weight in water, scurry to a drier part of the mound, and distribute it to other termites. In addition to rebalancing the mound’s moisture level, moving all of this water dramatically changes its shape.

Turner’s work with termites has attracted some notable collaborators, among them British engineer Rupert Soar. Inspired in part by termite mounds, Soar has plans to build energy-efficient houses with porous walls that make use of passive wind energy. He’s also looked into using termite-style building methods to help robots build structures in remote locations using only local materials.

Turner added fluorescent green dye to termites’ water to illuminate how they transfer large amounts of water across the mound.

Photograph by Mark W. Moffett, National Geographic

Group Brain

Termites may even change the way we think about thinking. A research project at Harvard’s Wyss Institute for Biologically Inspired Engineering brought computer scientists and roboticists to Turner’s site to observe termite behavior with a range of sophisticated scanners and software.

Harvard professor of robotics Radhika Nagpal makes an analogy between the behavior of termites and the brain. Individual termites react rather than think, but at a group level they exhibit a kind of cognition and awareness of their surroundings. Similarly, in the brain, individual neurons don’t think, but thinking arises in the connections between them. (Single neurons, for example, may recognize a baseball bat and the smell of hot dogs, but working in concert they let you know you’re at a baseball game.)

Nagpal’s team set up dozens of experiments to try to observe just where this collective cognition arose. “What program are they running?” mused Harvard physicist Justin Werfel, comparing the termites to robots. “Can we get a stochastic model of a stateless automaton that has no memory but reacts to what it encounters?”

Nagpal, Werfel, and Kirstin Peterson, also from Harvard, recently used termite behavior as a model to build a small swarm of robots (named TERMES) that assembles a structure without any instructions.

“This is a system where complexity is of the essence,” Turner says of the termites’ behavior. “If you don’t capture the complexity, there’s no hope of understanding it.” And so the quest continues for the elusive mind in the mound.

Lisa Margonelli is a senior research fellow at the New America Foundation and the author of Oil on the Brain: Petroleum’s Long, Strange Trip to Your Tank. She is working on a new book about termites.


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