Mound-building termites are a group of termite species that live in mounds. These termites live in Africa, Australia and South America. The mounds sometimes have a diameter of 30 metres. Most of the mounds are in well-drained areas. Termite mounds usually outlive the colonies themselves. If the inner tunnels of the nest are exposed it is usually dead. Sometimes other colonies, of the same or different species, occupy a mound after the original builders' deaths.
The structure of the mounds can be very complicated. Inside the mound is an extensive system of tunnels and conduits that serves as a ventilation system for the underground nest. In order to get good ventilation, the termites will construct several shafts leading down to the cellar located beneath the nest. The mound is built above the subterranean nest. The nest itself is a spheroidal structure consisting of numerous gallery chambers. They come in a wide variety of shapes and sizes. Some, like Odontotermes termites build open chimneys or vent holes into their mounds, while others build completely enclosed mounds like Macrotermes. The Amitermes (Magnetic termites) mounds are created tall, thin, wedge-shaped, usually oriented north-south.
Workers, smallest in size, are the most numerous of the castes. They are all completely blind, wingless, and sexually immature. Their job is to feed and groom all of the dependent castes. They also dig tunnels, locate food and water, maintain colony atmospheric homeostasis, and build and repair the nest.
The soldiers' job is to defend the colony from any unwanted animals. When the large soldiers 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 is commonly stated to be toxic or undergoes coagulation with the air which renders it glue-like.
Finally, there are the reproductives which include the king and the queen. The queen can sometimes grow up to six centimeters long while the lower classes are generally less than one centimeter.
Other life on termite mounds
Vegetation on termite mounds usually differs highly from vegetation in the surrounding. In African savannas, Macrotermes mounds form 'islands' with high tree densities. This is usually attributed to the fact that due to the digging of termites and due to their decomposition of plant material, the mound soils are generally more fertile than other soil. On top of that, mound soils have been found to contain more water than their surroundings, a clear advantage for plant growth in savannas. The high tree densities on termite mounds attract high densities of browsing herbivores, due to the high nutrient contents in foliage from trees growing on mounds, or perhaps due to the high quantities of food and shelter on mounds.
Brazilian caatinga mounds
The caatinga ecoregion in northeast Brazil has about 200 million termite mounds spread over an area the size of Great Britain. Some of the mounds are 3 m (10 ft) tall and 10 m (33 ft) wide, and they are spaced about 20 m (66 ft) apart. Underneath the mounds are networks of tunnels that required the excavation of 10 cubic kilometres of dirt. Scientists performed radioactive dating on 11 mounds. The youngest mound was 690 years old. The oldest was at least 3,820 years and possibly more than twice that. The mounds were built by Syntermes dirus termites, which are about half an inch long. Deforestation in the region helped to reveal the extent of the mounds to scientists. One scientist stated that the mounds apparently represent "the world's most extensive bio-engineering effort by a single insect species."
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