Termite
From The Art and Popular Culture Encyclopedia
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"When he is dominated by sexual desire, he will believe everything you happen to tell him. Knock on a stone with your fingernail - in his own morse code - and at once he answers."--The Soul of the White Ant (1925) by Eugène Marais |
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The termites are a group of social insects usually classified at the taxonomic rank of order Isoptera (but see also taxonomy below). As truly social animals, they are termed eusocial along with the ants and some bees and wasps which are all placed in the separate order Hymenoptera. Termites mostly feed on dead plant material, generally in the form of wood, leaf litter, soil, or animal dung, and about 10% of the estimated 4,000 species (about 2,600 taxonomically known) are economically significant as pests that can cause serious structural damage to buildings, crops or plantation forests. Termites are major detrivores, particularly in the subtropical and tropical regions, and their recycling of wood and other plant matter is of considerable ecological importance.
As eusocial insects, termites live in colonies that, at maturity, number from several hundred to several million individuals. They are a prime example of decentralised, self-organised systems using swarm intelligence and use this cooperation to exploit food sources and environments that could not be available to any single insect acting alone. A typical colony contains nymphs (semi-mature young), workers, soldiers, and reproductive individuals of both genders, sometimes containing several egg-laying queens.
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Social organization
Reproductives
A female that has flown, mated, and is producing eggs, is called a "queen". Similarly, a male that has flown, mated, and remains in proximity to a queen, is termed a "king". These anthropocentric terms have caused great misunderstanding of colony dynamics. Research using genetic techniques to determine relatedness of colony members is showing that the idea that colonies are only ever headed by a monogamous royal pair is wrong. Multiple pairs of reproductives within a colony are not uncommon. In the families Rhinotermitidae and Termitidae, and possibly others, sperm competition does not seem to occur (male genitalia are very simple and the sperm are anucleate), suggesting that only one male (king) generally mates within the colony.
At maturity, a primary queen has a great capacity to lay eggs. In physogastric species, the queen adds an extra set of ovaries with each moult, resulting in a greatly distended abdomen and increased fecundity, often reported to reach a production of more than two thousand eggs a day. The distended abdomen increases the queen's body length to several times more than before mating and reduces her ability to move freely, though attendant workers provide assistance. The queen is widely believed to be a primary source of pheromones useful in colony integration, and these are thought to be spread through shared feeding (trophallaxis).
The king grows only slightly larger after initial mating and continues to mate with the queen for life. This is very different from ant colonies, in which a queen mates once with the male(s) and stores the gametes for life, and the male ants die shortly after mating.
The winged (or 'alate') caste, also referred to as the reproductive caste, are generally the only termites with well-developed eyes (although workers of some harvesting species do have well-developed compound eyes, and, in other species, soldiers with eyes occasionally appear). Termites on the path to becoming alates (going through incomplete metamorphosis) form a sub-caste in certain species of termites, functioning as workers ('pseudergates') and also as potential supplementary reproductives. Supplementaries have the ability to replace a dead primary reproductive and, at least in some species, several are recruited once a primary queen is lost.
In areas with a distinct dry season, the alates leave the nest in large swarms after the first good soaking rain of the rainy season. In other regions, flights may occur throughout the year or more commonly in the spring and autumn. Termites are relatively poor fliers and are readily blown downwind in windspeeds of less than 2 km/h, shedding their wings soon after landing at an acceptable site, where they mate and attempt to form a nest in damp timber or earth.
Nests
thumb|upright|An arboreal termite nest in Mexico Termite workers build and maintain nests which house the colony. These are elaborate structures made using a combination of soil, mud, chewed wood/cellulose, saliva, and faeces. A nest has many functions such as providing a protected living space and water conservation (through controlled condensation). There are nursery chambers deep within the nest where eggs and first instar larvae are tended. Some species maintain fungal gardens that are fed on collected plant matter, providing a nutritious mycelium on which the colony then feeds (see Diet, above). Nests are punctuated by a maze of tunnel-like galleries that provide air conditioning and control the CO2/O2 balance, as well as allow the termites to move through the nest.
Nests are commonly built underground, in large pieces of timber, inside fallen trees, or atop living trees. Some species build nests above ground, and they can develop into mounds. Homeowners need to be careful of tree stumps that have not been dug up. These are prime candidates for termite nests and being close to homes, termites usually end up destroying the siding and sometimes even wooden beams.
Mounds
Mounds (also known as "termitaria") occur when an aboveground nest grows beyond its initially concealing surface. They are commonly called “ant hills” in Africa and Australia, despite the technical incorrectness of that name.
In tropical savannas, the mounds may be very large, with an extreme of 9 m (30 ft) high in the case of large conical mounds constructed by some Macrotermes species in well-wooded areas in Africa. Two to three metres, however, would be typical for the largest mounds in most savannas. The shape ranges from somewhat amorphous domes or cones usually covered in grass and/or woody shrubs, to sculptured hard-earth mounds, or a mixture of the two. Despite the irregular mound shapes, the different species in an area can usually be identified by simply looking at the mounds.
The sculptured mounds sometimes have elaborate and distinctive forms, such as those of the compass termite (Amitermes meridionalis and A. laurensis) which build tall, wedge-shaped mounds with the long axis oriented approximately north–south, which gives them their common name. This orientation has been experimentally shown to assist thermoregulation. The thin end of the nest faces towards the sun at its peak intensity, hence taking up the least possible heat, and allows these termites to stay above ground where other species are forced to move into deeper below ground areas. This also allows the compass termites to live in poorly drained areas where other species would be caught between a choice of baking or drowning. The column of hot air rising in the aboveground mounds helps drive air circulation currents inside the subterranean network. The structure of these mounds can be quite complex. The temperature control is essential for those species that cultivate fungal gardens and even for those that do not; much effort and energy is spent maintaining the brood within a narrow temperature range, often only plus or minus 1° Celsius over a day.
In some parts of the African savanna, a high density of aboveground mounds dominates the landscape. For instance, in some parts of the Busanga Plain area of Zambia, small mounds of about 1 m diameter with a density of about 100 per hectare can be seen on grassland between larger tree- and bush-covered mounds about 25 m in diameter with a density around 1 per hectare, and both show up well on high-resolution satellite images taken in the wet season.
Shelter tubes
Termites are weak and relatively fragile insects that need to stay moist to survive. They can be overpowered by ants and other predators when exposed. They avoid these perils by covering their trails with tubing made of feces, plant matter, saliva, and soil. Thus, the termites can remain hidden and wall out unfavourable environmental conditions. Sometimes these shelter tubes will extend for many metres, such as up the outside of a tree reaching from the soil to dead branches.
To subterranean termites, any breach of their tunnels or nests is a cause for alarm. When the Formosan subterranean termite (Coptotermes formosanus) and the eastern subterranean termite (Reticulitermes flavipes) detect a potential breach, the soldiers will usually bang their heads apparently to attract other soldiers for defence and recruit additional workers to repair any breach. This head-banging response to vibration is also useful when attempting to locate termites in house frames.
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