How Termites Build Living Infrastructure

Around 3,000 termite species are known, and only a few dozen damage buildings. The rest are the main recyclers of dead wood and grass in the tropics and the architects of some of the largest animal-built structures on land. Mounds of the African genus Macrotermes typically stand 2 to 3 metres tall, and the tallest recorded reach about 9 metres, built grain by grain by insects 5 millimetres long.

Termites are not ants. They are social cockroaches, placed within the order Blattodea, and unlike ants they have workers of both sexes, a long-lived king alongside the queen, and soft-bodied nymphs that work from an early age. The colony processes material almost nothing else can eat and regulates its own climate, which makes it an infrastructure system rather than a pest story.

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Three things set termites apart: caste specialisation, microbe-assisted digestion and climate-controlled architecture. A mature Macrotermes colony holds one to two million individuals. Workers forage, build and feed the others; soldiers with heavy mandibles or glue-squirting snouts guard the tunnels; and the queen, swollen to around 10 centimetres, can lay 20,000 to 30,000 eggs a day for a reign of 15 to 20 years or more.

Digestion is outsourced. Lower termites carry protists in the hindgut that break down cellulose, and higher termites rely on bacteria. The fungus-growing termites of the subfamily Macrotermitinae went further about 30 million years ago: workers chew plant litter, pass it quickly through the gut and build it into sponge-like combs on which a fungus, Termitomyces, grows. The fungus breaks down lignin the termites cannot, and the colony then eats the aged comb and the fungal nodules. The relationship is obligate on both sides, and each new colony is seeded with spores the founders carry in.

Leafcutter ants farm fungus the same way in the Americas, which is one of the clearest cases of the same solution evolving twice.

Termite survival is a maintenance problem. A colony of a million termites plus its fungus garden burns oxygen at a rate comparable to a cow, and the fungus only thrives in a narrow band of warmth and humidity. Macrotermes bellicosus nests in the Ivory Coast hold their core within a degree or two of 30 °C and near saturation humidity while the air outside swings by 20 degrees between night and day. The mound is what makes that possible.

Workers build with soil cemented by saliva and faeces, and they rebuild constantly. Breach a mound wall and workers seal it within hours. They also keep the colony dark and sealed because their soft bodies dry out fast in open air; foraging trips run inside covered tunnels and mud sheeting that they extend across the ground and up tree trunks.

Defence is layered: soldiers block tunnels with their heads, and in Nasutitermes the soldiers spray a sticky terpene glue from a nozzle on the head at raiding ants. When a colony matures, it releases thousands of winged alates on a single humid evening; a tiny fraction survive to pair, shed their wings and found a new nest.

The colony survives because the internal environment is kept within workable limits, every hour, by a million small repairs.

The mound is not where the termites live. The nest sits at or below ground level with the fungus combs and brood around it, and the mound above acts as a ventilation and heat-management structure. A tall central chimney runs up the core, surrounded by a web of radial conduits that open into thin outer walls full of pores too small for a termite to pass. In 2015 a Harvard team led by Hunter King measured air movement in Macrotermes michaelseni mounds in Namibia and showed that the daily temperature cycle drives it: by day the thin outer flutes warm faster than the core, so air rises in the periphery and sinks through the chimney; at night the flow reverses. Carbon dioxide drains out and oxygen comes in on a 24-hour rhythm, with wind gusts adding extra mixing.

The table summarises how the main parts work together.

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In tropical savannas and forests termites consume a large share of all dead plant material, moving nutrients from litter into soil and into the food chain. Their tunnelling lets rain soak in rather than run off, and the soil they bring up from depth is richer in nitrogen, phosphorus and clay than the surface around it. In the Kenyan savanna, evenly spaced Macrotermes mounds raise plant growth and insect and lizard abundance for metres around each mound, so the whole landscape is patterned by them.

Termites are also food on a vast scale. An aardvark or aardwolf can eat a quarter of a million termites in a night, pangolins and chimpanzees dig and fish for them, and the seasonal flights of alates feed birds, bats, frogs and people. Remove termites from a savanna and you lose not only its decomposers but much of its soil engineering and a base layer of its food web.

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Termite

Termites are everywhere in warm climates but rarely in the open. These cues turn a walk into a sighting.

• Read the mud sheeting

  Thin mud tubes running up tree trunks, fence posts and rock faces are active foraging galleries. Open a small section and workers will be inside; it will be resealed by morning.

• Mound after rain

  Workers extend and repair mound surfaces when the soil is damp. Fresh, darker patches of wet earth on a mound mean construction is under way.

• Flight nights

  The first warm, humid evening after the rains break brings alates swarming around lights. It is the easiest time to see winged termites and the predators that gather for them.

• Shoot the soldiers

  Soldiers are the most distinctive caste: big orange heads in Macrotermes, pointed snouts in Nasutitermes. A macro shot of one at a tunnel mouth makes a clear in-app capture.

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Termites work on the material everyone else ignores. Dead grass and wood are waste only until something can process them, and a fungus partnership turned that waste into fuel for a million-strong city.

The architectural lesson is the one engineers have borrowed. The Eastgate Centre in Harare, Zimbabwe, was designed in the 1990s with passive ventilation modelled on termite mounds and uses a fraction of the cooling energy of a conventional building its size. When the structure itself regulates the environment, the whole operation becomes cheaper to sustain.

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