Termites, sometimes known as white ants, are a group of eusocial insects usually classified at the taxonomic rank of order, Isoptera. Termites feed on wood and other dead plant material, and several species are economically important as pests that can cause serious structural damage to buildings. Termites are also significant in subtropical and tropical regions, where they help recycle wood and other plant matter. Around 2,750 species have been described so far.
| Termites | |
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| File:Formosan subterranean termites.jpg | |
| Formosan subterranean termite soldiers(red colored heads) and workers (pale colored heads). | |
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| Order: | Isoptera Brullé, 1832
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Reticulitermes spp.
Mastotermitidae | |
Appearance and morphology
Termites only superficially resemble ants; their "white ant" name is probably due to their similar size and social habits.
Termites have biting mouthparts and their soft bodies are small, rarely over 10 mm in length. They typically inhabit dark nests and tunnels, only venturing out when the winged alates emerge to leave their parent colony, when constructing shelter or, in the case of grass-eaters, when harvesting grass stems. The bodies of flying individuals are dark, while termites which remain in the nest are whitish with only their heads being lightly pigmented. The deciduous wings of termites are long and slender, in two pairs that are similarly sized and shaped. The name of the termites' order is derived from their having equal wings. The veins near the anterior margin of the wing are prominent with the rest only faintly marked. The wings are quickly shed after flight with a simple body flick when the swarming termites find a new nest site, pair up and dig in. The remnant of the wing is a distinct triangular scale.
Social structure and behaviour
As social insects, termites live in colonies that number from several hundred to several million individuals at maturity. 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, workers, soldiers, and reproductive individuals of both sexes, often containing several egg-laying queens. The mating ritual between the queen and he boy toy male termites is called termiteous.
Queen and king
At maturity, a primary queen can lay several thousand eggs a day. In physogastric species, the queen adds an extra set of ovaries with each moult, resulting in a greatly distended abdomen and increased fecundity. The distended abdomen increases her size in some species to as much as 10 centimetres, hundreds of times the original size, effectively immobilizing her. In times where the queen must be moved to a new chamber it requires a group effort to move her whereby hundreds of workers are required to push her. The queen is widely believed to be a primary source of pheromones useful in colony integration. As a reward for attending workers a juice is secreted from the queen's posterior for the workers to drink. The king remains only slightly bigger than an average termite and continues to mate with the queen for life. This is especially unusual since ant societies have colonies with only a queen which mates once with the male and stores his gametes for life. Males in ant colonies die immediately after mating, unlike termite male alates which become kings and live with the queen. The alate caste, also referred to as the reproductive caste, are the only termites with well developed eyes. In some cases termite mounds have been opened to find multiple queens and kings in a single nest chamber. Immature alates still going through incomplete metamorphosis form a sub-caste in certain species of termites, functioning as supplementaries. Supplementaries have the ability to replace a dead primary reproductive, but this integration into primary reproductive status is rare.
Workers
Worker termites undertake the labours of foraging, food storage, brood, nest maintenance and a portion of the defence effort in some species. Workers are the only caste in the colony with the ability to digest cellulouse in wood due to the presence of trichonympha in the digestive tract. They then regurgitate the digested cellulose to the other castes since only they have the mandibles to chew wood and the digestion required. This symbiosis is integral since without these microbes entire nests would starve. This weakness is sometimes used in pest control to destroy termites by killing the trichonympha chemically. Termite workers are blind due to undeveloped eyes. The workers are responsible for creating the nest walls using a combination of dung, wood chips and saliva. Some species have been known to create such durable walls that industrial machinery has been damaged in an attempt to break their tall mounds. Some African and Australian species have mounds that can tower above a man's height. The nest is designed by workers with special rooms for fungal gardens, brooding, water collection, reproductive chambers, and tunnel networks that effectively provide air conditioning. In some species the workers have additional symbiosis with insects known as termitophiles where juice is created for the termites and housing is provided for the termitophiles. This is similar to cow ants, which farm aphids for juice and provide a home for the aphid.
Soldiers
The soldier caste has anatomical and behavioural specializations, primarily against ant attack. Many have jaws so enlarged that they cannot feed themselves, but instead, like juveniles, are fed by workers. The tropical Nasutus species have soldiers with the ability to exude noxious liquids through either a horn-like nozzle (nasus) or simple hole in the head (fontanelle). Many species are classified using the characteristics of the soldiers' heads, mandibles or nasus due to distinct differences with each species. Among the drywood termites, a soldier's enlarged (phragmotic) head can be used to block their narrow tunnels. Termite soldiers mostly require the aid of the nest to perform war duty since they have undeveloped eyes which are blind. They use their heads, nasus or mandibles to defend tunnels effectively. With a tunnel blocked so effectively it can rebuff attacks from many ants. Usually more soldiers stand by behind the initial soldier so once the first one falls another soldier will take his place. In cases where the intrusion is coming from a breach that is larger than the soldier's head, defense requires special formations where soldiers form a phalanx-like formation around the breach blindly biting at intruders or shooting toxic glue from the nasus. This formation involves self sacrifice because once the breach is repaired during fighting by the workers no return is provided causing the death of all the defenders. Termites undergo incomplete metamorphosis, with their freshly hatched young taking the form of tiny termites that grow without significant morphological changes. Some species of termite have been known to have small groups of extremely large soldiers (3*normal size). Though their purpose is unknown speculation indicates that they are an elite class that defends only the inner tunnels of the mound. This is the commonly accepted belief because their size would be of great use in the large interior tunnels. Even when provoked, these large soldier termites will not defend themselves but merely traval deeper into the mound.
Diet
Termites are generally grouped according to their feeding behaviour. Thus the commonly used general groupings are: Subterranean, Soil-feeding, Drywood, Dampwood and Grass eating. Of these, subterraneans and drywoods are primarily responsible for damage to structures.
All termites eat cellulose in its various forms as plant fibre. Cellulose is a rich energy source (think of wood fibres), but difficult to digest. Termites rely primarily upon symbiotic protozoa (metamonads) within the genus Trichonympha and other microbes in their gut to digest the cellulose for them, absorbing the end products for their own use. The gut protozoa in turn rely on symbiotic bacteria embedded on their surfaces to produce some of the necessary digestive enzymes. This relationship is one of the finest examples of mutualism among animals. Most so called "higher termites", especially in the Family Termitidae can produce their own cellulase enzymes. However, they still retain a rich gut fauna with bacteria dominant.
Some species of termite practise fungiculture - they maintain a 'garden' of specialized fungi of genus Termitomyces, which are nourished by the excrement of the insects. When the fungi in turn are eaten, their spores pass undamaged through the intestines of the termites, to complete the cycle by germinating in the fresh faecal pellets. [1]
Mounds
In some regions, notably arid tropical savannas, termites construct extremely large and elaborate mounds which house their colonies. These mounds can have very distinctive forms, such as those of the compass termite (Amitermes meridionalis & A. laurensis) which build tall wedge-shaped mounds with the long axis oriented approximately north-south. This orientation has been experimentally shown to help in thermoregulation. The column of hot air rising in the above ground mounds helps drive air circulation currents inside the subterranean network. Some mounds can reach heights of 6 metres, but most species build mounds of less than two metres height. The structure of these mounds can be quite complex. The temperature control is essential for those species that cultivate fungal gardens.
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Cathedral Mounds
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Magnetic Mounds (nearly North-South Axis)
Human interaction
Because of their wood-eating habits, termites sometimes do great damage to buildings and other wooden structures. Their habit of remaining concealed often results in their presence being undetected until the timbers are severely damaged and exhibit surface changes. Once termites have entered a building they do not limit themselves just to wood, also damaging paper, cloth, carpets, and other cellulosic materials.
Termites try to remain hidden, building tunnels in earth and wood. When they have to cross some impermeable material they build several feet long shelter tubes (from packed earth/feces).
Fighting termites
Precautions:
- Avoiding contact of wood with ground by using termite-resistant concrete, steel or masonry foundation with appropriate barriers. Even so, termites are able to bridge these with shelter tubes, and it has been known for termites to chew through even lead piping to reach moisture.
- Timber treatment.
- Use of wood that is naturally resistant to termites and other boarers such as Canarium australianum, otherwise known as the Turpentine Tree. Note that there is no such wood that provides guaranteed proof against termite damage, only some that would be less favorable.
When termites have already penetrated a building, removing their means of access and destroying the colony with insecticides are usually effective means of stopping further damage. Another common method of treating termites in houses, used in Australia since the early 1930's, is topical application of arsenic trioxide powder. This slow-acting poison is distributed by the workers before any symptoms occur and is capable of destroying the colony. More modern variations include triflumuron, fipronil and imidacloprid which are much less toxic to mammals. Slow-acting toxins are also delivered by a range of methods involving poisoned feed.
In 2005, a group of Australian scientists discovered a treatment based on a plant extract (false sandalwood) that repels termites [2]. Ongoing tests conducted by BioProspects Limited have shown that termites will stay on the other side of treated wood (even so far as starving rather than crossing) and when exposed and forced to keep close proximity to the extract (in the stated case within a petrie dish) become disoriented and eventually die.
Ecology
Ecologically, termites are important in nutrient recycling, habitat creation, soil formation and quality and, particularly the winged reproductives, as food for countless predators. Globally termites are found roughly between 50 degrees North & South, with the greatest biomass in the tropics and the greatest diversity in tropical forests and Mediterranean shrublands. Termites are also considered to be a major source of atmospheric methane, one of the prime greenhouse gases. Termites have been common since the Cretaceous period.
Relationships and evolutionary history
The oldest termite fossils date to the early Cretaceous, although there is some evidence they evolved sometime during the Jurassic. It has long been accepted that termites are closely related to cockroaches and mantids, and they are classified in the same superorder (Dictyoptera), but new research has shed light on the details of termite evolution. [3] There is now strong evidence suggesting termites are highly modified, social, wood-eating cockroaches. A study conducted by scientists has found that endosymbiotic bacteria from termites and a genus of cockroaches, Cryptocercus share the strongest phylogenetical similarities out of all other cockroaches. Both termites and Cryptocercus also share similar morphological and social features- most cockroaches do not show social characteristics, but Cryptocercus takes care of its young and exhibits other social behavior. Additionally, the primitive termite Mastotermes darwiniensis exhibits numerous cockroach-like characteristics that are not shared with other termites.
References
External links
- Termite Extermination Resource
- University of Nebraska page on Termites
- A summary of termite control methods
- University of California advice on Drywood Termites
- African Pygmies - Termites gathering
- Catalogue of the termites of the World
- Pictures of termites
- Transitional Species in Insect Evolution
- Did the Termites Cause Laterites?
- Cretaceous Termites and Soil Phosphorus
- Beneficial Uses of Termites
- Texas A&M University Department of Entomology - Center for Urban & Structural Entomology
- The Soul of the White Ant - Eugène N. Marais
- Urban Entomology Program University of Toronto
- Harvard University fact sheet on Eastern Subterranean Termites