Princeton University - Council of Science & Technology

POPE PRIZE

Essay 1
A day in the field
Elizabeth Derryberry

Essay 2
The Biggest Little Cities in the World
Elizabeth Singleton

The Biggest Little Cities in the World

…when we came to consider the wonderful order of these insects, and of their subterraneous cities, they will appear foremost on the list of the wonders of the creation. - H. Smeathman, 1781

The first termite mound that I ever saw amazed me. I had no idea what could have raised the earth from the ground in such a bizarre fashion. The earthen mound was on the side of the dirt road that I walked up and down several times a day as I went about my work on the Reserve. It easily rose two meters above the gound and resembled a child's sandcastle, but on a grand scale, Several towers rose above the main earthen mound which was about the size of a golf cart, forming a solid structure, impressive in shape, but ambiguous in purpose. After two months of living and. working on the Mokolodi Nature Reserve outside of Gaborone, Botswana, I no longer stopped to marvel at the structure every time I passed. It faded into the landscape, just as every day details of your house, like the crooked picture frame or wobbly banister, disappear into the background. But, every time a new cover asked me about the strange configuration, I happily obliged all that I had learned about the world's smallest architects.

All, over Africa the mounds mar the horizon of the savanna, their ramparts hiding the intricacies inside and their banality making them uninteresting to tourists searching for elusive big game. Just as tourists tire of antelope, they rarely inquire about termite mounds once they have been identified, except for perhaps mis-siting them as a distant rhinoceros or sniggering at their phallic appearance. What tourist do not realize is that these mounds are an integral part of the ecosystem and culture that the tourists are "exploring".

When eighteenth and nineteenth century biologists first encountered the mounds the complexity of the nests impressed them so much that they though that the mounds has been built by highly intelligent organisms whose society was comparable to human's. Early researcher, Smeathman, having no other comparison anthropomorphized the termitaria, referring to the towers that contained nurseries, provision chambers, guard-rooms, corridors, bridges, subterranean streets, canals, and a royal palace. Despite being compared to Homo Sapiens, termites are most closely related to the dreaded cockroach, but belong to their own order, Isoptera. One of over 2000 species, the mound building termite of the African bush, Macrotermes, is from the family Termitidae, one of four distinct families of the order. The termites order presents a maze of intricacies in behavior from species to species, with thousands of variations on the normal patterns of mating, mound building, and foraging. Although they are extremely social insects, termites have escaped scientific scrutiny, primarily because their range in the tropics overlaps little with the concentration of researchers in Europe and North America.

The extreme cooperation and interaction within a termite nest has lead many researchers to refer to the nest not as a colony, which can contain up to six million individuals, but as one organism. A specialized caste system ordains termites to their position within the colony. Thousands of termites work towards each necessity: reproduction, consumption, protection, shelter construction. Four castes exist as a division of labor, each of which is morphologically and functionally distinct: primary reproductives, supplementary reproductives, and soldiers, and workers who are wingless and sterile. At the head of the caste system reigns the matriarch who is solely responsible for the reproduction of the colony's future members. The entire colony is structured around the royal chamber where the queen and king lie in dark confinement endlessly producing and fertilizing eggs respectively. The queen is the dominant figure of the colony, in size and in importance. She lies, hundreds of times the size of her offspring and even her king, deep within the nest in complete darkness. Once the queen is settled into the royal chamber she will not -move again. She lies there reproducing while older children-servants bustle in and out of the small entrances bringing her food, carrying away her waste, and tending to her offspring. A Macrotermes queen spends her life producing anywhere from 5,000 to 30,000 eggs in a single day. In her twenty-year life span, a single queen can lay up to 250 million eggs, each which product young termites that are lucky to live six months.

Occurring as frequently as four mounds to an acre termitaria represent the resilience of the bush, strong enough to resist marauding elephants, rhinos, and even a wayward tourist-bearing Land Rover. The mound is a fortress to protect the queen, with outer walls up to a meter in thickness hiding an intricate maze of chambers passages, and honeycomb like fungus gardens. The consistency of the material used to build the structure rivals cement in its strength and durability and has been used to pave roads and build houses. The interior of the mound extends well below the surface level to protect the community from invasion by large predators. However, termites are a good source of protein, and the aardvark has evolved as predator specialized in breaking into termite mounds with long sharp claws used for digging through the tough outer wall. Through evolution termites have developed a communication and defense system that allows them to ward off invaders as large as the aardvark or a small as other insects, such as ants.

At the first sign of a penetration into the mound soldier termites repeatedly strike their heads against the floor or walls of the nest, creating a warning signal to which workers and soldiers throughout the nest react. As soon as the alarm has been sounded, a bustle of activity ensues. Any breach of the mound is quickly repaired by thousands of workers, and battle begins as soldier-termites selflessly ward off any type of invasion. This complex defense structure and nest grows from an initial single chamber dug by the king and queen themselves.

A new colony begins with the nuptial flight of the supplementary reproductive caste after workers spend weeks building exit tunnels from an existing colony. Once the first rains soften the soil of the savanna thousands of the reproductives take flight on wings prepared solely for this moment. Most termites do not make it far from the mound as predators ranging from hyenas to aardvarks to humans feast off the annual flight of the termites which provides an important source of protein to many animals. As soon as the females have landed, often not far from home, they shed their wings and assume the mating position to attract the hovering males, The males quickly descend and detach their own wings in a single, split-second movement, and follow their brides in search of a new home. From the beginning a termitaria is a matriarch dominated society. Tunneling into the rain-moistened soil, the couple will build a chamber where they wall themselves in, living off their fat supplies (which makes them such a treat for predators), until they bear enough offspring who will care for them. Very few migrating reproductives make it to a new colony, but millions of years of evolution have proved this pattern as an efficient way of perpetuating the gene pool.

The colony grows as the queen reproduces continuously, and slowly expands its home as the burgeoning population demands. Within each mound is a self-sustaining community that brings in only plant material as food from the outside. The busy termites tend to everything, keeping the mound temperature and humidity controlled, protected from invaders, well fed, and readily supplying the next generations. The architecture of the mound incorporates elaborate thermoregulatory mechanisms to keep the internal temperature at a constant 30ºC. The entire exterior surface of the termitaria is a gas exchange area between the interior and the exterior. The gaseous makeup of the external air can have major impacts on the success of a colony, affecting reproduction rates and the growth of the fungus gardens.

Although termites are known as wood-eaters, the Macrotermes must ingest fungus from their gardens in order to be able to break down the cellulose into useful nutrition. These gardens become the focal point of the nest, and are carefully maintained, often requiring termites to tunnel forty meters down to the water table in order to sustain the proper humidity within the mound. Besides the gardeners, other worker termites keep ventilation shafts functioning, others tend the larvae in the nursery, some wait on the royal couple, bringing them food, removing waste, and transporting eggs. A specialized caste looks after every component of the mound. The colony will grow and expand with some mounds reaching three to four meters in height and up to six square meters in area beneath the surface. If a human were to build a relative structure, it would be about a mile high and five miles in diameter.

In their ventures outside of the mound for foraging, termites use chemical signals to leave trails for others to follow, and to aid in the return to the mound. These chemical signals, or smells, are a part of a complex communication system. Every termite colony has a unique signal, and members are capable of distinguishing foreign termites from their own. Upon encountering termites from different mounds, different species exhibit various degrees of hostile behavior towards enemy species. This recognition capability helps contributes to the defense system. However, it is rare that foreign termites bring on the demise of another termite colony. Colonies have been known to last up to eighty years, and often decline for unknown reasons.

Even after a termite colony expires because of invasion or other natural causes, its importance to the ecosystem continues. Termites recycle organic material back into the soil. The digesting cellulose is returned to the soil as termites use their excrement to construct their mounds. As the rain, wind and sun erode the abandoned mounds, all of the nutrients are returned to the soil and attract new plant growth. In Botswana's Okavango Delta, termite mounds are an essential component to the formation of islands, which create the habitat diversity that allows the Delta to host a wide variety of species. The high elevation of the mounds allows new plant growth to establish itself above the level of the annual floodwaters. The mound material is so rich in nutrients that it is consumed as a nutrient supplement by organism such as elephants to humans. Humans also use the mound material for building traditional dwellings due to its cement like consistency. The excavation holes left after recovering mound material become treacherous hazards on the outskirts of villages. The symbiosis between fungus and termites creates an efficient nutrient processing system. These two together do more for recycling organic materials than many invertebrates. While termites are capable of extensive damage to lumber, wooden structures, and even libraries in the tropics, they also contribute to the dynamics of their ecosystem.

In the time I spent in Botswana, I never ceased to be amazed when coming upon an especially impressive termite nest. While the ones that I saw everyday often blended in with the bush, I always appreciated the magnificence of their accomplishments. Most tourists lose interest in the mounds when told that insects, especially destructive ones, construct them. But, every once in a while, someone new who I told about the termites would eagerly inquire about the how and the why of termite mounds, and never be disappointed as the story of the termites is explained.

References:

Howse, DE. Termites: A Study in Social Behavior. London: Hutchinson University Library, 1970.

Jmhasly, P and RH Leuthold. "Intraspecific colony recognition in the termites Macrotermes subhyalinus and Macrotermas bellicosus (Isoptera, Termitidae), "Insectes-Sociaux, 46 (2): 164-170.

Korb, Judith and Karl Eduard Linsenmair. "The architecture of termite mounds: A result of a trade-off between thermoregulation and gas exchange?" Behavior Ecology 10(3): 312-316.

Krishna, Kumar. "Introduction," Biology of Termites Vol. 1 eds. Kumar Krishna and Frances M. Weesner. NY, NY: Academic Press, 1969.

Lee, KE and TG Wood. Termites and Soils. NY, NY: Academic Press, 1971.

Marais, Eugene N. The Soul of the White Ant. NY, NY: Dodd, Mead & Company, 1937.

Ruelle, JE. "Order Isoptera," Insects of Southern Africa, eds. Clarke H. Schole and Erik Rolm. Durban, South Africa: Butterworths, 1985, pp. 53-59.

Stuart, Alastair. "Social Behavior and Communication," Biology of Termites Vol. 1 eds. Kumar Krishna and Frances M. Weesner. NY, NY: Academic Press, 1969.