Miniature Metropolises

by on ; last featured October 16, 2016
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The world's master builders are less than an inch tall. Gifted ant architects have built thriving cities on every continent—using every imaginable kind of material.

The subterranean city highways are busy with traffic scurrying to and from the suburban markets. The citizens carry out their jobs with abandon, in full accordance with their special callings. A complex communication network ensures the survival of this metropolis, which must manage its food production, defend its citizens from marauding enemies, and regulate the climate. In some cities, caverns are set aside for shepherds to tend their flocks; and in other communities, collective farmers plant, prune, and harvest food from underground gardens.

These sound like modern human cities, but they’re not. Welcome to the wonderful world of ants, some of God’s most able architects, who have built an astonishing array of charming cities around the world.

Not All Ant Societies Are Created Equal

Not all ant dwellings and behaviors are this sophisticated. Some ants take advantage of preexisting places that range from acorns and leaf litter to tree canopies and tidal zones on shorelines.

The harvester ants, however, are the proverbial builders. King Solomon, perhaps history’s most renowned builder, cited these ants as our model. As they build granaries and gather seeds for winter, they don’t require managers or special motivation to work: “Go to the ant, you sluggard! Consider her ways and be wise, which, having no captain, overseer, or ruler, provides her supplies in the summer, and gathers her food in the harvest” (Proverbs 6:6–11).

What is their secret? Ants, along with bees and termites, have been called superorganisms. Just like a body is made of many parts, each functioning for the good of the whole, ant societies are made up of many individuals, functioning for the good of the society. Thousands or millions of individuals share duties in a complex division of labor with each individual performing work for the survival of the community, not the individual.

The potential benefits of this flexible system are astounding. Bustling ant civilizations are found on every habitable continent, from deserts to rainforests, as they are built out of every imaginable material, each city suited to local resources. Their resourcefulness is a ceaseless source of awe, forcing us to ponder the Creator who engineered such master builders.

Fungus Farmers of the South

Where should we begin our imaginary journey to investigate these modern metropolises? Right here in my own backyard, in the southern USA. From this subtropical climate all the way to South America, we encounter the most highly complex ant societies yet discovered.

They are known as leafcutter ants (Atta) because they gather leaves for their subterranean gardens. They not only build amazing multilevel mounds but are also adept at farming. Subterranean highways run from the urban center to the outlying suburbs, where the ants climb to the surface to forage for fresh leaves on the forest floor and canopy. They cut the leaves to manageable sizes and haul them back to their underground gardens. There the ants cut them again into smaller pieces and deposit them in chambers. Tiny tufts of fungal fuzz are stuck on the leaf fragments where they grow quickly. Some workers add feces containing digestive enzymes and nutrients to enhance the growth of the fungus.

Leafcutter Ants

© imv | istockphoto.com

Leafcutter ants build amazing, interconnected chambers below the earth's surface to a depth where humidity and temperature stay constant throughout the year. In these chambers, the ants grow fungal gardens from the leaves they cut from the forest. This labor-intensive agriculture requires workers of all different sizes to do several different jobs.

In one 6-year-old nest, researchers found a vast labyrinth with 1,920 chambers, 25 feet (7.5 m) underground. They estimated that the ants had to excavate a whopping 40 tons of soil. The architecture was quite complex. Between 3 and 10 feet (1–3 m) below the surface were chambers used for rearing various stages of young (egg, larva, and pupa). Hundreds of other interconnected chambers contained fungal gardens that fed the colony. To farm on a scale like this requires millions of ants to harvest leaves from a territory bigger than an acre. The estimated harvest of dry leaves would weigh 1,036 pounds (470 kg) per year!

This labor-intensive agriculture requires workers of all different sizes and several different job categories, or castes. Some prune, carry, or shred leaves, while others tend the fungal gardens, guard the queen, manage the nursery, defend the nest, or dump trash. Fungus gardening requires unique and special behaviors such as preparing the ground, pruning, harvesting, and pest management. Some ants produce antibiotics to keep the fungus gardens virtually free from contaminating bacteria and other fungi. Meanwhile, workers must groom the trails so that foraging forays remain efficient.

Scientists believe the mound and subterranean galleries are also designed for microclimate regulation. Based on the properties of the soil, workers dig to a depth where humidity and temperature stay constant throughout the year. The mound’s outer crust then insulates the colony and minimizes the loss of moisture and temperature.

The mound’s shape increases sunlight exposure and decreases erosion. Some ant species build layers of dry vegetation that create a waterproof barrier and further control erosion. They may also spread charcoal, small pebbles, and other materials that trap solar energy quickly and thus, heat the mound more rapidly. The Greek historian, Herodotus, described ants that mined gold in India and left gold flecks on their mounds. For centuries people thought this sounded outrageous. Could this unusual ant behavior, described more than 2,000 years ago, mean that ants were providing gold-flecked solar energy traps for their homes?

The underground chambers are spatially arranged to allow workers to move the brood (larva and pupa stages) easily to obtain optimum temperature and humidity for their development.

The underground chambers are spatially arranged to allow workers to move the brood (larva and pupa stages) easily to obtain optimum temperature and humidity for their development. Some ants can detect carbon dioxide concentrations using their antennae. This fact, along with the nest architecture, indicates that the ants are designed to monitor and deal with changes in temperature, humidity, and carbon dioxide concentrations, all of which are important to the well-being of each ant and the brood. It seems that larvae (the earlier stage of ant young) require a slightly different humidity than pupae (the later stage of ant young). Another way the ants control this environment is by opening and closing holes on different locations of the mound.

Mounds also have to be defended. Some ants simply close the nest openings at night. Others send guard ants to stick their heads out of mound openings and use their jaws to defend against marauders. Still others stick their back ends out of the entrances and produce drops of venom to ward off the enemy.

Rock Homes in the Cold North

If we travel north toward Canada, we'll find that many ant species build their underground galleries beneath flat and shallow rocks or rotting logs, avoiding mound building altogether. Building under these objects offers more protection against drying out or dangerous temperatures. It doesn’t take much early morning sunshine on a cool spring or autumn day to heat the rock. Worker ants can bring the brood right under the rock for proper development, and they can begin breeding much earlier, right after the winter snows disappear, and breed longer. During warmer spells, if the rock is too warm, workers will take the brood below ground and place them in chambers with the appropriate temperature and humidity.

Outdoor Army Ants in the Tropics

Along our journey, if you hear loud crunching sounds through the forests of Mexico, Brazil, or Peru, you need to get out of there because millions and millions of ants are on the march. These are the feared army ants (different species of army ants are also found in Africa and Asia). This society does not build natural shelters, but after a long day of marching, workers use their own bodies to create a massive cylindrical shape where the queen and the brood are placed at the center. This living shelter made of interlocking ant workers, called a bivouac, not only sheds rain but also keeps the brood and queen warm enough to survive the night. The temperature at the core of this cylinder can be 4–9°F (2–5°C) higher than the surrounding air temperature.

Army Ants

Mark Moffett | Minden Pictures | National Geographic Creative

Army ant workers make homes out of living bodies. They link to one another toe-to-toe (left), to build a new shelter, called a bivouac. Ants continue to join (right) until hundreds of thousands have created a shelter where the queen and brood are safe in the center.

Wallpapered Wood Homes in Central America's Rain Forest

Sometimes the humidity levels are too high in a Central American rainforest. One rainforest ant society builds its nest in rotten logs on the forest floor. The gallery walls have the right moisture for the queen and eggs, but apparently they are too moist for pupal chambers. So workers wallpaper the pupa gallery with several layers of discarded pupa cocoons to keep out the moisture. This produces drier conditions for pupae, conditions under which they apparently develop better.

Pine Needle Mounds in Europe & Russia

To the east and over the Atlantic, the wood ants await us in northern Europe and cold Siberia. These ants don’t build soil mounds but rather collect masses of pine needles and mound them on tree stumps. They will collect the resin from these pines and apply it to their bodies as a disinfectant against bacteria and fungi. The pile of needles can be 7 feet (2.1 m) high, and holes are dug for both ventilation and air conditioning. They are built with steep sides to shed water.

Deep inside the mound, warmth comes from the heat generated by rotting plants and the bodies of subterranean workers. The temperature and humidity vary from gallery to gallery, so the developing brood can be moved to optimum conditions for growth.

Tree Houses of Tropical Africa and Asia

As we journey farther south, we encounter the weaver ants of Africa and Asia. This society weaves nests out of leaves in trees. The nests are amazingly intricate and can be scattered among several trees.

Bending live leaves into position can require incredible strength. A leaf is too big for one ant to move into place to make an appropriate shelter, so she needs help. The construction begins when one worker grabs onto a leaf with her jaws, and then hundreds of her fellow workers come alongside to grab each other’s bodies and pull together. With their combined strength, the ants pull the edge of the leaf against a nearby leaf. Then they hold the leaf down, while others sew the leaves together.

Sewing the leaves together is a feat all by itself. Workers search for larval ants, grasp them in their jaws, and bring them up to the construction site. The larvae produce silk (also used for cocoons), so certain workers skillfully maneuver these living silk-dispensers back and forth “sewing” the leaves together, while other workers hold the leaves in position until they are held fast by the silk threads into waterproof shelters as large as a man’s head.

Weavers in East Africa will change their homes from one side of a tree to the other, depending on the season, to maximize their exposure to light and regulate temperatures.

Mud Houses of Australia

Some ants (Polyrhachis sokolova) in Australia’s swamps actually build their cities 18 inches (45 cm) deep into the mud below mangrove trees. This may not seem like a big deal until you realize that their subterranean city is flooded at least twice a day during high tide.

The mound has two entrance holes that are designed to collapse when high tide floods the nest. The collapsing entrances plug the holes so the galleries won’t flood. However, as time progresses, seawater still leaks into underground tunnels, and the ants must continually move their eggs and brood to galleries not yet inundated. These bell-shaped galleries are designed to trap air, which supplies oxygen long enough for their brood to survive.

The labor intensity of this community is off the charts! As the tide lowers, they swim to the surface, traverse water to forage, repair the mound, and excavate new bell-shaped galleries before the next high tide.

One Body, Many Parts

In the midst of studying ants’ stunning architecture, which highlights the wisdom of their Creator, we discover that death and suffering permeate their lives. Warring armies fight and kill each other every day, while stronger ants enslave weaker ants to do their bidding.

In the midst of our fallen world, an ant colony still reminds us how a society is supposed to work together like one body.

Their world is a stark reminder of the curse, which Adam brought upon creation when he selfishly desired to live independent of God and ignore his obligations to his wife and future family.

Yet in the midst of our fallen world, an ant colony still reminds us how a society is supposed to work together like one body. In 1 Corinthians 12, the Apostle Paul explains that the body of Christ is a unit made of many parts. The church is a fellowship of very different people who have unique gifts that they should be exercising in accordance with their special calling, as they diligently serve their Creator and their fellow humans in a community of self-sacrificing love.

Next time you see an ant hill, may God remind you of your own calling and important work to be done for Christ and His body!

Tom Hennigan is associate professor of biology at Truett-McConnell College, where he teaches organism biology and ecology. He is co-author of the newest edition of the Wonders of Creation series, The Ecology Book.

Reference

Burt Hölldobler and Edward O. Wilson, The Ants (Cambridge, Massachusetts, Belknap Press, 1990).

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