Special Inspecta Investigation

Insects, including termites, are the most successful group of animals in the world today. Termites have been on Earth for over 50 million years. Some of their fossils date back to the Oligocene, Eocene, and Miocene periods. They have evolved into many different species. As of 1995, there were approximately 2,753 valid names of termite species in 285 genera around the world. The word “termites” comes from the Latin tarmes, a word given to a small worm that makes holes in wood.

Macrotermes bellicosus is an African mound-building termite. It has a highly developed social caste system which includes workers, soldiers, and reproductives. M. bellicosus contributes to the ecosystem by advancing the decomposition process. In spite of its many predators, it has survived to become an important part of the African ecosystem.

Taxonomy

Kingdom – Animalia
Phylum – Arthropoda
Class – Insecta
Subclass – Pterygota
Order – Isoptera
Suborder – Fontanella
Subdivision – Longiprocta
Superfamily – Termitoidea
Family – Termitidae
SubfamilyMacrotermitinae
GenusMacrotermes
Speciesbellicosus

Mounds of the Macrotermes Bellicosus 

Termites of the subfamily Macrotermitinae are well known as the builders of nearly all the large termite mounds of tropical Africa. They sometimes have a diameter of 30 meters. Most of the Macrotermes mounds are found in well-drained areas. Termite mounds usually outlive the colonies themselves. If the inner tunnels of the nest are exposed, it is usually dead. However, sometimes other colonies occupy a mound after the original builders have died. These recolonizers may be of the same or a different species — or both.

“Nye (1955) reported an average of only one live mound in fifteen for M. bellicosus in southern Nigeria, but Sands (1965) estimate of 60% alive for the same species in northern Nigeria is probably more usual.” (D.E. Pomeroy, Ecological Entomology, vol 1, 1976).

Young mounds of M. bellicosus are roughly circular in shape and often highly irregular. Areas of new growth have a characteristic “bubbly” appearance and, when young, the whole mound may look like this. Very young mounds have no openings. Mounds of the M. bellicosus are considered mature when they show little or no change in size.

Many mounds, both dead and alive, have vegetation growing on them. Young, actively growing mounds of the M. bellicosus are usually bare, but are usually colonized by various plants as they become older. The variation might be enormous: small mounds are sometimes almost entirely covered, while dead mounds can be found nearly bare. A study done in Uganda (1976) determined that grasses are predominant, Digitaria sp. and Pennisetum sp. being the most common. However, Imperata cylindrica, Panicum maximum, Cynodon sp. and Brachiaria sp. also occur frequently. Herbs include Commelina benghalensis, Oxalis corniculato and Bidens pilosa. Lantana camora is often found on older mounds.

“It is not known how old the colonies are when they first appear above ground level, but one to two years seems likely. Most mounds make their first appearance at or just after a period of high rainfall when the ground is presumably soft.” (D.E. Pomeroy, Ecological Entomology, vol 1, 1976).

The structure of the mounds can be very complicated. Sometimes on mature mounds, in order to get good ventilation, the M. bellicosus will construct several shafts leading down to the cellar located beneath the nest. The average diameter of the shafts of the M. bellicosus is about two centimeters, but they are often higher than wide. The number of shafts can also increase as the nest grows larger.

Social Castes

The M. bellicosus termites live in colonies, but they are really more like families. Of some 30 or so insect orders, termites are the only one in which all species are categorized as highly social or “eusocial,” They are very unique due to the fact that their colonies are based on monogamy. As far as entomologists know, they are the most sophisticated families ever to evolve in the universe. The termite colony has three separate stages: juvenile, adult, and senile. The survival of their species depends on their caste system.

The smallest in size, yet most numerous of the castes, are the workers. They are all completely blind, wingless, and sexually immature. Their job is to feed and groom all of the dependent castes. Workers also dig tunnels, locate food and water, maintain colony atmospheric homeostasis, and build and repair the nest.

The soldiers’ job is to basically defend the colony from any unwanted animals. Macrotermes bellicosus has a primary and a secondary soldier type. During the juvenile period, which was estimated to be five to six years by Ruelle (quoted by Bodot, 1969) and four to six years by Collins (1981), only the smaller of the two soldier types are produced.

Soldiers have larger heads that are longer and wider than that of the workers because they contains more muscle. The soldiers can not feed themselves and must rely on the workers for this. Some termite genera soldiers can be different sexes; however, the Macrotermitinae are mainly all females.

“When the large soldiers of Macrotermes attack, they emit a drop of brown, corrosive salivary liquid which spreads between the open mandibles. When they bite, the liquid spreads over the opponent. The secretion has not been chemically identified yet, but it is commonly stated that it is toxic or else undergoes coagulation with the air, which renders it glue-like” (Edward O. Wilson., The Insect Societies, 1971).

Finally, there are the reproductives. These include the king and the queen. The sole role of the king is to provide the queen with the sperm needed to fertilize her eggs. F.A. Fenton, in 1956, recorded that the queen of the M. bellicosus can sometimes live as long as ten years.

The queen can sometimes grow up to six centimeters long, while the lower classes are generally less than one centimeter. The king closely resembles the queen in appearance. One difference between them is the size of the queen’s abdomen once it is swollen with eggs. Her abdomen can hold up to ten milliliters of eggs, making it the largest of all individual social insects. Termite reproductives have wings of equal size, which is where the Order name “Isoptera” originates. The Greek word isos means “same” and ptero means “wings.”

Ecosystem

Termites are very important in tropical ecosystems. They are probably the most important animals contributing to the decomposition processes. They also have a positive effect on soil fertility. The M. bellicosus eats mainly dead wood, although it will eat anything containing cellulose. They have a multi-compartmented gut for digesting a cellulose. This is an excellent example of symbosis, or mutalism. Wood and dry plant matter (lignocellulosic matter) is the most abundant category of primary production on earth, and termites are the primary group of animals adapted to feed on this non-nutritive matter. They also contribute to the tropical ecosystem by providing food and shelter to an extraordinary number of associated organisms.

We may think of termites as pests, but 90% of termite species are considered highly beneficial. Their unique ecological roles in breaking down wood and turning, aerating and enriching the soil are very important. Subterrainean termites such as M. bellicosus also have an advantage because, by tunneling underground, they can find more than one source of wood.

Predators of the Macrotermes Bellicosus

Although M. bellicosus generally have little to do with the outside world, they nonetheless have many enemies. This is somewhat surprising, since their mounds are veritable fortresses. One dangerous predator is the aardvark. Three features that the aardvark has that help it raid termite mounds are powerful digging feet, strong claws, and a long tongue. This makes it easy to breach the outer wall of the termite mounds, which the soldiers can do nothing to stop. Certain anteaters and pangolins do much the same thing.

Because M. bellicosus is considered to be a major pest of graminaceous crops such as maize and millet, people will sometimes destroy young nests they discover but leave more mature ones alone.

During swarming season, young males and females that are leaving the nest to make new colonies are exposed to birds, bats, reptiles and amphibians.

One of the most dangerous predators of the M. bellicosus are driver ants, according to Paulette Bodot (1964). If their path crosses a mound of the M. bellicosus, they will invade it by entering at the top where the building material is soft. Once inside, the ants find little resistance since they have better eyesight and greater agility. It is rare for the colony is completely destroyed because some of the worker termites hide in the royal chamber. These termites continue the colony, and before long, life has returned to usual.

Conclusion

The Macrotermes Bellicosus has been a important contributor to the ecosystem of tropical Africa. It can also be a major pest to African agriculture and wooden structures. Its complex and highly evolved social caste system has enabled it to survive for millions of years. For example, the worker caste spends almost all of its life building the massive mounds that the colony will live in. The mound’s hard outer layer, as well as the soldiers, will then protect them from many predators.

The M. bellicosus has had many positive and negative effects on the African area. It has even been suggested that all termites produce a combined amount of about one fifth of the world’s methane. Termites are also an important food source in West Africa. In conclusion, the M. bellicosus termite will continue to be an important element in the African environment.

Credited pictures to: University of Toronto Urban Entomology Program; University of Wyzenberg, Department of Animal Ecology And Tropical Biology.