Mound building by Macrotermes bellicosus: Thermoregulation and other architectual aspects

Scriptie Orientatiefasecursus Populatiebiologie 1998

Anna den Held and Thijs van der Velden


Introduction

We were asked to write a literature study about a subject that interested us during the course population biology. An amazing phenomenon in nature is the ingenius moundbuilding by certain termites. We decided to focus on the Macrotermes bellicosus, which belongs to the subfamily Macrotermitinae. These are fungus-growing termites which occur in parts Africa and Asia. First we will give some general information about this so-called social insect, and then go to to our main point, the thermoregulation in the nest of the M. bellicosus by different architecture.

The founding of a nest starts by the royal couple who make a hole in the soil, called copularium. In here the queen lays her first eggs which develop into stunted workers. They accomplish the further developement of the nest and after a while receive help from newborn soldiers. Just after four years alate reproductives are produced.

As said before the M.bellicosus is fungus-growing. They build fungus combs which

occupy special gardens in the center of the nest in large compartements. The gardens are organized into complex sponge-like structures with numerous convoluted ridges and tunnels, evidently designed to give the maximum surface for growth. The substrate of the fungi is finly chewed wood provided by the termites themselves.

At first there was doubt about the exact function of these gardens. Some thought they were somehow part of the ventilation system of the big nests by providing some of the heat needed for convection. Nevertheless convincing evidence has been collected that the fungi are an important nutritive symbiont for some of the Macrotermine species. Microscopic examination of macrotermes workers gut contents indicated that the fungi serve to degrade the lignin and to expose the minute fragments of cellulose for quicker digestion by the intestinal bacterial flora.

Even more remarkable than the phenomenon of fungus-growing is the size and complexity of the nests constructed by the macrotermites. An important aspect of this complexity is the thermoregulation concerning the nests. Several studies have been made about the ability of M. bellicosus to regalate the internal temperature of their nests and the influence that the environmental temperature has on the architecture of the mounds.

Top


Termitenests and their composition.

The nests of termites are generally regarded as a future of social organisation. The inside of a adult nest is always build according to a certain plan, containing one or more breeding centres from which radiate a network of galleries and runways to special chambers which store food, water and all kind of soilparticles.

In general we can classify the nests into six categories, gathered into two main groups. The first group contains three categories of areal nests, i.e. in the aerial parts of plants. The second group contains three categories of terranian nests; one under the soil surface, one half on it, and one above the soil surface, called mound. It is in this kind of nests that our M.bellicosus lives. Their mounds are impressive feautures characterising whole landscapes. They reach heights up to 8 meters, and appear sometimes in densities of 83 mounds per hectare.

The mounds are constructed of soil particles, (like coarse sand, fine sand, silt, clay and organic carbon), extracta and saliva, these in varying proportions. The M.bellicosus uses re-packed, orally transported soil particles, cemented with saliva into walls.

It is thought that mound structure of termites is determined by three important factors: the species, the soil composition and the microclimatic conditions (like rain and temperature). This last item is supposed to be very important because it can change on large scale in the same area.

That there is correlation between moundshape and thermoregulation within the nest, has often been suggested. Stable temperature inside the nest is very important for an optimum in fungus production, and so the termites use special archtitectual technics to construct a mound with certain thermoregulatory qualities.

Investegation on this subject has been done in Comoé-National Park (Ivory Coast) by Korb and Linsenmair (1997). In this park we find the M.bellicosus in two very different areas. First, they are found in the very warm shrub savanna. Here, the mounds have rather thin walls with numerous ridges and complex structures. The ridges on the outside of the mounds are made to increase the surface. The result is that the temperature inside will not increase above the critical level during the day. Inside the nest there are several ventilationchannels, essential for the gasexchange. These channels are also involved in the thermoregulation. During the cold savanna night, the diameter is reduced by constructing obstacles in the channels so ventilation decreases and heatloss is regulated. When temperature increases during the day these obstacles are removed so that ventilation takes place and heat is lost.

Second, they appear in the moisty gallery forest. This habitat has a relative cool, but stable climate. So in this environment it is important for M.bellicosus to reduce the loss of heat. Therefore the mounds are dome-shaped with massive walls and hardly any portraiding structures. The reason for this is that in this type of habitats it is not nescessary to have an extended channelsystem for this would only increase heatloss.

It can be concluded that the differences in moundarchitecture performed by termites of the same species is caused by the diffrences in temperature between the two habitats. The

M. bellicosus apparently is capable of influincing its own microclimate By building mounds with special structures they can actually achieve thermoregulation.


References

Wilson, Edward.O.,1971, ‘The Insect Societies’, Harvard University Press.

Brian,M.V. (ed) 1978, Production ecology of ants and termites, Cambridge University Press.

Korb,J., Linsenmair, K.E., 1997, ‘The effect on …… savanna’. Insectes Sociaux 45:1-112.

Korb,J., Linsenmair, K.E., 1997, ‘Experimental heathing ….architecture’. Insectes Sociaux 45:.235-347

Thanks to H.Velthuis for his important contribution.

Amazing Creations–Termite Towers

TERMITE TOWERS

The termite is the acknowledged master architect of the creature world. No other insect or animal approaches the termite in the size and solidity of its building structure. The world’s tallest non-human structures are built by Australian or African termites. If a human being were the size of an average termite, the relative size of a single termite nest is the equivalent of a 180 story building–almost 2000 feet high. It would easily be the tallest building in the world. How is it possible that this tiny creature has the engineering know-how to erect an edifice of this magnitude? Obviously this knowledge is innate to the termite. The process of construction, the materials and correct combination of materials to yield an elegant, structurally efficient and durable structure is simply awe-inspiring.

The building material is usually local soil mixed with saliva. Sometimes dung is mixed in. It becomes so hard and impervious that the native people of the area use it for building their mud and stick shelters. The termite mound, or termitary, consists of hard, thick walls that seal in moisture and keep heat out. The Australian and African variety of termite towers are designed for cooling. A system of channels and ducts circulates air through the mound. These passageways run through areas of the mound that have walls that are porous or have tiny ventilation holes. The pores act as fresh air ventilation and stale air exhaust. This supply and return system performs solely on heat and gravity with no moving parts. Can our tall building work with such efficient simplicity?

At the lower core of the termitary are the living and working quarters. This area is the coolest and most insulated zone of the nest. The royal chamber, which is the largest chamber in the nest, houses the queen and king. Below the royal chambers are where the workers store food and care for the young termites, called nymphs. In some colonies the workers tend gardens where tiny mushrooms and varieties of fungus are grown. The termites grow this fungus inside a comb which is located in several pockets in the central zone of the inner nest. The comb, made of termite droppings, provides nourishment for the growing fungus and the termites feed on both the fungus and the comb. Termites live on cellulose, the substance which makes the framework of vegetation, and fungi. Ingress and egress from a termite tower is provided by a series of underground tunnels. The tunnels lead outward and branch into a network of passage that open to the outside. The insects make their trips to the outside at night, when it is cooler, and collect twigs, leaves, seeds and other food. In very hot, dry climates some species in the desert dig straight down exceeding 125 feet(38m) to connect with underground water. Underground wells supply the termitary with water and a source for cooling the interior. The peaks and towers of the termite’s nest act as lungs that expel rising hot air, which is generated by the breaking down of the fecal comb by the fungus. The air then rises via a large central air duct, and moves up through the long porous chimneys.The carbon dioxide in the air then diffuses to the outside, while oxygen diffuses into the chimneys. The oxygenated air eventually loses its heat to the cooler outside air and cools sinking down into the cellar.[4] Such an ingenious HVAC system is necessary for the survival of some three million termites to a single colony.

The exterior form of the termite nest depends upon the climate. For instance some termite nests have adapted to their rainy surroundings by creating umbrella-like roof structures that direct water from heavy rains away from the nest. Compass termites appear like giant wedges with the broad side facing due east and west. This solar orientation serves to keep the high, intense sun from hitting any appreciable portion of the mounds surface and allows the weaker morning and setting sun to warm the greater surface area of the structure; thus, the structure attempts to create an even heating situation whereby the mound does not overheat.

See http://www.tdrinc.com/home.html for the article in full.

2001

Amazing Creations – The African termite called Macrotermes Bellicosus is truly an amazing creation.

 

These termites build the larges non-manmade structures in the world. If they were the equivalent size of man, their tower would be 180 stories high. This would easily be the highest structure in the world.

The cement is so hard and water resistant that the local natives of the are often use it for their huts.
The architectural design is an engineering masterpiece.
The air circulation is an essential element for survival in the African sun. They obviously have no moving parts, but the structure removes and refreshes the air continually.
Ventilation ducts use heat to create current that passes along thing inner walls that are porous. This allows the protected chambers to breathe and refresh oxygen.

These creatures have literally achieved thermoregulation. During cold nights, the openings are blockaded to reduce heat loss and during the sunlight hours, the openings are opened fully to maximize ventilation. Some species also cap their structures with umbrellas of mud. It repels water away from the structure and blocks out the hot afternoon sun. The overhang is designed to allow the early morning sun to warm the structure.

The M. Bellicosus supplements its diet by growing fungi. They chew up wood and digest what nutrients can be taken in. The rest is passed and used for gardening. The primary food source is not the wood itself, but fungi. Growing rooms are built for the purpose of raising this food source for the colony.

The M. Bellicosus termite’s structure is so climate efficient that it maintains a constant temperature of 88-89 degrees in the growing chambers. This is significant in the fact that their primary fungus harvest can only grow if the temperature is below 89 degrees and above 88 degrees. The two degree variable is essential for the health of the colony. Even more interesting is that the primary fungus grown is only found one place in the natural world – inside the growing chambers of the M. Bellicosus termite.
 

  Can evolution teach this kind of engineering? This fungus is dependent on the M. Bellicosus termite and the termite is dependent on the fungus and the engineering technology it uses to survive. It takes a lot of faith to believe that this glory belongs to blind evolution.
  For More information see the following articles: