Termites are eusocial insects that are classified at the taxonomic rank of infraorder Isoptera, or as epifamily Termitoidae within the cockroach order Blattodea. Termites were once classified in a separate order from cockroaches, but recent phylogenetic studies indicate that they evolved from close ancestors of cockroaches during the Jurassic or Triassic. However, it is possible the first termites emerged during the Permian or even the Carboniferous. Approximately 3,106 species are currently described, with a few hundred more left to be described. Although these insects are often called white ants, they are not ants.
Like ants and some bees and wasps, which are in the separate order Hymenoptera, termites divide labour among castes that consist of sterile male and female "workers" and "soldiers". All termite colonies have fertile males called "kings" and one or more fertile females called "queens". Termites mostly feed on dead plant material and cellulose, generally in the form of wood, leaf litter, soil, or animal dung. Termites are major detritivores, particularly in the subtropical and tropical regions, and their recycling of wood and plant matter is of considerable ecological importance.
Termites are among the most successful groups of insects on Earth, colonising most landmasses except for Antarctica. Their colonies range in size from a couple of hundred individuals to enormous societies with several million individuals. Termite queens also have the longest lifespan of any insect in the world, with some queens living up to 50 years. Each individual termite goes through an incomplete metamorphosis which, unlike the complete metamorphosis found in ants, proceeds through egg, nymph and adult stages. Colonies are described as superorganisms because the termites form part of a self-regulating entity: the colony itself.
Termites play a vital role in the ecosystem by recycling waste material such as dead wood, faeces and plants. Termites are a delicacy in the diet of some human cultures and are used in many traditional medicines. However, several hundred species are economically significant as pests that can cause serious damage to buildings, crops or plantation forests. Some species, such as the West Indian drywood termite (Cryptotermes brevis), are regarded as invasive species, having been introduced to countries to which they are not native.
Etymology
The infraorder name is derived from the Greek words iso (equal) and ptera (winged), which refers to the nearly equal size of the fore- and hind-wings. The name termite derives from Latin and Late Latin from the word termes ("woodworm, white ant"), altered by the influence of Latin terere ("to rub, wear, erode") from the earlier word tarmes. Termite nests were commonly known as terminarium or termitaria. In early English, termites were known as wood ants or white ants. The modern term termite was first used in 1781.
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Taxonomy and phylogeny
Recent DNA analysis from 16S rRNA sequences has supported a hypothesis originally suggested by Cleveland and colleagues in 1934, that these insects are most closely related to the wood-eating cockroaches (genus Cryptocercus), due to similar symbiotic gut flagellates in certain cockroaches and ancient living termites (living fossils). In the 1960s, additional evidence supporting the hypothesis emerged when F. A. McKittrick noted similar morphological characteristics between some termites and Cryptocercus nymphs. These similarities have led some authors to propose that termites be reclassified as a single family, Termitidae, within the order Blattodea, which contains cockroaches. Other researchers advocate the more conservative measure of retaining the termites as Termitoidae, an epifamily within the cockroach order, which preserves the classification of termites at family level and below.
The oldest unambiguous termite fossils date to the early Cretaceous, but given the diversity of Cretaceous termites and early fossil records showing mutualism between microorganisms and these insects, it is likely that they had their origin at least some time in the Jurassic or Triassic. Further evidence of a Jurassic origin is the assumption that the extinct Fruitafossor consumed termites, judging from its morphological similarity to modern termite-eating mammals.
Claims for an earlier time period for the emergence of termites stand on controversial footing. For example, F. M. Weesner believes that Mastotermitidae termites may go back to the Late Permian, 251 million years ago, and fossil wings that have a close resemblance to the wings of Mastotermes of the Mastotermitidae, the most primitive living termite, have been discovered in the Permian layers in Kansas. It is even possible that the first termites emerged during the Carboniferous. Termites are thought to be the descendants of the genus Cryptocercus, the wood roach. The folded wings of the fossil wood roach Pycnoblattina, arranged in a convex pattern between segments 1a and 2a, resemble those seen in Mastotermes, the only living insect with the same pattern. On the other hand, Krishna et al. consider that all of the Paleozoic and Triassic insects tentatively classified as termites are in fact unrelated to termites and should be excluded from the Isoptera.
It has long been accepted that termites are closely related to cockroaches and mantids, and they are classified in the same superorder (Dictyoptera). There is strong evidence suggesting that termites are highly specialised wood-eating cockroaches. The cockroach genus Cryptocercus shares the strongest phylogenetical similarity with termites and is considered to be a sister-group to termites. Both termites and Cryptocercus also share similar morphological and social features: for example, most cockroaches do not exhibit social characteristics, but Cryptocercus takes care of its young and exhibits other social behaviour such as trophallaxis and allogrooming. The primitive giant northern termite (Mastotermes darwiniensis) exhibits numerous cockroach-like characteristics that are not shared with other termites, such as laying its eggs in rafts and having anal lobes on the wings. Cryptocercidae and Isoptera are united in the clade Xylophagodea.
Although termites are sometimes called "white ants", they are actually not ants. Ants belong to the family Formicidae within the order Hymenoptera. The similarity of their social structure to that of termites is attributed to convergent evolution. The oldest termite nest discovered is believed to be from the Upper Cretaceous in west Texas, where the oldest known faecal pellets were also discovered.
As of 2013, about 3,106 living and fossil termite species are recognised, classified in 12 families. The infraorder Isoptera is divided into the following clade and family groups, showing the subfamilies in their respective classification:
Distribution and diversity
With the exception of Antarctica, termites are found on all continents. The diversity of termite species is low in North America and Europe (10 species known in Europe and 50 in North America), but the diversity of termites in South America is high, with over 400 species known. Of the 3,000 termite species currently classified, 1,000 are found in Africa, where mounds are frequently seen in certain regions. Approximately 1.1 million active termite mounds can be found in the northern Kruger National Park alone. In Asia, there are 435 species of termites, which are mainly distributed in China. These species are restricted to specific habitats such as tropical and subtropical habitats. In Australia, all ecological groups of termites (dampwood, drywood, subterranean) are endemic to the country, with over 360 classified species.
Termites are usually small, measuring between 4 to 15 millimetres (0.16 to 0.59 in) in length, but the largest of all extant termites are the queens of the species Macrotermes bellicosus, measuring up to over 10 centimetres (4 in) in length. Another giant termite, the extinct Gyatermes styriensis, is from the Miocene in Austria, with a wingspan of 76 millimetres (3.0 in) and a body length of 25 millimetres (0.98 in). Due to their soft cuticles, termites do not inhabit cool or cold habitats. Termites are also considered to be a major source (11%) of atmospheric methane, one of the prime greenhouse gases. There are three ecological groups of termites: dampwood, drywood and subterranean. Dampwood termites are found only in coniferous forests, drywood termites in hardwood forests, and subterranean termites in widely diverse areas. One species in the drywood group is the West Indian drywood termite (Cryptotermes brevis), which is an invasive species in Australia.
Description
Most worker and soldier termites are completely blind and do not have a pair of eyes, but the alates have eyes along with lateral ocelli. Lateral ocelli, however, are not found in all termites. Like other insects, termites have a small tongue-shaped labrum and a clypeus; the clypeus is divided into a postclypeus and anteclypeus. Termites also have a number of sensory functions. This includes a scape, one of the three basic segments on the insect antennae, a pedicel, the second segment, which is typically shorter than the scape, and finally the flagellum, which refers to all the segments beyond the scape and pedicel. The mouthparts contain a maxillae, a labium and a set of mandibles. The maxillae and labium have palps which help termites sense food and handling.
The anatomy of the thorax is consistent with all insects, and consists of three segments: the prothorax, the mesothorax and the metathorax. Each segment contains a pair of two legs. On alates, the wings are located at the mesothorax and metathorax. The mesothorax and metathorax have well-developed exoskeletal plates while the prothorax has smaller plates. The termite thorax consists of three plates, known as the pronotum, mesonotum and metanotum.
Termites have a ten-segmented abdomen with two plates, the tergites and the sternites. There are ten tergites, nine of which are wide and one of which is elongated. The reproductive organs are similar to those in cockroaches but are more simplified. For example, the intromittent organ is not present in male alates, and the sperm is either immotile or aflagellate. However, Mastotermitidae termites have multiflagellate sperm with limited motility. The genitals in females are also simplified. Unlike in other termites, Mastotermitidae females have an ovipositor, a feature strikingly similar to that in female cockroaches.
All castes of termites have six legs on which they rely. The alates fly only for a brief amount of time, so they also rely on their legs. The appearance of the legs is similar in each caste, but the soldiers have larger and heavier legs. The structure of the legs is consistent with other insects. This includes a coxa, trochanter, femur, tibia and the tarsus. The number of tibial spurs on an individual's leg varies. Some species of termite have an arolium, located between the claws, which is present in species that climb on smooth surfaces but absent in most termites.
Unlike in ants, the hind- and fore-wings are of equal length. Most of the time, the alates are poor flyers; their technique is to launch themselves in the air and fly in a random direction. Studies show that in comparison to larger termites, smaller termites cannot fly long distances. When a termite is in flight, the wings remain at a right angle, and when at rest, remain parallel to the body.
Caste system
Worker termites undertake the most labour within the colony, being responsible for foraging, food storage, and brood and nest maintenance. Workers are tasked with the digestion of cellulose in food and are thus the most likely caste to be found in infested wood. The process of worker termites feeding of one colony member by another is known as trophallaxis; trophallaxis is an effective nutritional tactic to convert and recycle components that are nitrogenous. It frees the parents from feeding all but the first generation of offspring, allowing for the group to grow much larger and ensuring that the necessary gut symbionts are transferred from one generation to another. Some termite species do not have a true worker caste, instead relying on nymphs that perform the same work without differentiating as a separate caste.
The soldier caste has anatomical and behavioural specialisations, and their sole purpose is to defend the colony. Many soldiers have large heads with highly modified powerful jaws so enlarged they cannot feed themselves; instead, like juveniles, they are fed by workers. Simple holes in the forehead, fontanelles that exude defensive secretions, are a feature of the family Rhinotermitidae. Many species are readily identified using the characteristics of the soldiers' larger and darker head and large mandibles. Among certain termites, a soldier's globular (phragmotic) head can be used to block their narrow tunnels. Different sorts of soldiers include minor and major soldiers, and nasutes which have a horn-like nozzle frontal projection (a nasus). These unique soldiers have the ability to biosynthesize diterpenes, and nitrogen fixation plays an important role in nutrition for nasutes.
The reproductive caste of a mature colony includes a fertile female and male, known as the queen and king. The queen of the colony is responsible for egg production for the colony while the king mates with her for life, unlike in ants. In order for mass egg-laying production, the abdomen of the queen swells up dramatically, a characteristic known as physogastrism. Depending on the species, the queen will start producing reproductive alates at a certain time of the year, and huge swarms emerge from the colony when nuptial flight begins. These swarms also attract a wide variety of predators.
Life cycle
Like other social insects, most individuals in a termite colony are infertile workers, but, unlike bees or ants, the worker termites are diploid individuals of both sexes and develop from fertilised eggs. In contrast, while female bees (both workers and the queen) are diploid and develop from fertilised eggs, males (drones) are haploid and develop from unfertilised eggs. The life cycle of a termite begins with an egg, but is different from that of a bee or ant in that it goes through a developmental process called incomplete metamorphosis, with egg, nymph and adult stages. After eggs hatch into nymphs, the nymphs will go through a series of moults until they become adults. In some species, eggs go through four moulting stages while nymphs go through three. Nymphs first moult into workers, and then some workers go through further moulting and become soldiers or alates; workers become alates only by moulting into alate nymphs.
The development of nymphs into adults can take months; the time period depends on food availability, temperature, and the general population of the colony. Since nymphs are unable to feed themselves, workers must feed them, but workers also take part in the social life of the colony and have certain other tasks to accomplish. Pheromones are said to regulate the caste system in termite colonies, preventing all but a very few of the termites from becoming fertile queens.
Reproduction
Termite alates only leave the colony when a nuptial flight takes place. Alate males and females will pair up together and then land in search of a suitable place for a colony. A termite king and queen will not mate until they find such a spot; when they do, they excavate a chamber big enough for both, close up the entrance and proceed to mate. After mating, the pair will never go outside and will spend the rest of their lives in the nest. Nuptial flight time varies in each species. For example, alates in certain species emerge during the day in summer while others emerge during the winter. The nuptial flight may also begin at dusk, when the alates swarm around areas with lots of lights. The time when nuptial flight begins depends on the environmental conditions, the time of day, moisture, wind speed and precipitation. The number of termites in a colony also varies, with the larger species typically having 100-1,000 individuals. However, some termites colonies, including those with large individuals, can number in the millions.
The queen will only lay 10-20 eggs in the very early stages of the colony, but will lay as many as 1,000 a day when the colony is several years old. At maturity, a primary queen has a great capacity to lay eggs. In some species, the mature queen has a greatly distended abdomen and may produce 40,000 eggs a day. The two mature ovaries may have some 2000 ovarioles each. The abdomen increases the queen's body length to several times more than before mating and reduces her ability to move freely; attendant workers provide assistance.
The king grows only slightly larger after initial mating and continues to mate with the queen for life (a termite queen can live up to 50 years). This is very different from ant colonies, in which a queen mates once with the male(s) and stores the gametes for life, as the male ants die shortly after mating. If a queen is absent, a termite king will produce pheromones which encourage the development of replacement termite queens. As the queen and king is monogamous, sperm competition does not occur.
Termites going through incomplete metamorphosis on the path to becoming alates form a subcaste in certain species of termite, functioning as potential supplementary reproductives, but this usually develops upon the death of a king or queen, or when the primary reproductives (the king and queen) are separated from the colony. Supplementaries have the ability to replace a dead primary reproductive, and there may also be more than a single supplementary within a colony. Some queens have the ability to switch from sexual reproduction to asexual reproduction. Studies show that while termite queens mate with the king to produce colony workers, the queens reproduce their replacements (neotenic queens) parthenogenetically.
Behaviour and ecology
Diet
Termites are detritivores, consuming dead plants at any level of decomposition; they also play a vital role in the ecosystem by recycling waste material such as dead wood, faeces and plants. Many species eat cellulose, having a specialised midgut that breaks down the fibre. Termites rely primarily upon symbiotic protozoa (metamonads) and other microbes such as flagellate protists in their guts to digest the cellulose for them, and absorb the end products for their own use. Gut protozoa, such as Trichonympha, in turn, rely on symbiotic bacteria embedded on their surfaces to produce some of the necessary digestive enzymes. Most so-called higher termites, especially in the family Termitidae, can produce their own cellulase enzymes, but they retain a rich gut fauna and rely primarily upon the bacteria. The flagellates have also been lost in Termitidae, a result of the diversification of their feeding habits. The knowledge of the relationships between the microbial and termite parts of their digestion is still rudimentary; what is true in all termite species, however, is that the workers feed the other members of the colony with substances derived from the digestion of plant material, either from the mouth or anus. Judging from closely related bacterial species, it is strongly presumed that the termites' and cockroaches gut microbiota derives from their dictyopteran ancestors.
Certain species such as Gnathamitermes tubiformans have seasonal food habits and often consume particular food sources in a given season. For example, the Red three-awn (Aristida longiseta) is frequently eaten during the summer, while Buffalograss (Buchloe dactyloides) is an important food source from May to August. Blue grama Bouteloua gracilis grass is an essential food source to their diet during spring, summer and autumn. Colonies rarely consume food during spring, but feeding activity in autumn is high. In one study, it was found that particular termite species prefer poplar and maple woods to other woods that were generally rejected by the termite colony.
Some species of termite practice fungiculture. They maintain a "garden" of specialised fungi of genus Termitomyces, which are nourished by the excrement of the insects. When the fungi are eaten, their spores pass undamaged through the intestines of the termites to complete the cycle by germinating in the fresh faecal pellets.
Predators
Termites are consumed by a wide variety of predators. One species alone, Hodotermes mossambicus, was found in the stomach contents of 65 birds and 19 mammals. Arthropods and reptiles such as bees, centipedes, cockroaches, crickets, dragonflies, frogs, lizards, scorpions, spiders, and toads consume these insects (two spiders in the family Ammoxenidae are specialist termite predators). Other predators include aardvarks, aardwolves, anteaters, bats, bears, bilbies, many birds, echidnas, foxes, galagos, numbats, mice and pangolins. The aardwolf is an insectivorous mammal that primarily feeds on termites; they locate their food by sound and also by detecting the scent secreted by the soldiers, and a single aardwolf is capable of consuming thousands of termites in a single night by using its long, sticky tongue. Sloth bears break open mounds to consume the nestmates, while chimpanzees have developed tools to "fish" termites from their nest; the extinct primate Paranthropus robustus is said to have used a bone tool to catch termites 1-1.8 million years ago, suggesting that these insects were an important food source to early hominids.
Among all predators, ants are the greatest enemy to termites. Some ant genera are specialist predators of termites; for example, Megaponera is a strictly termite-eating (termitophagous) genus that perform raiding activities, some of which can last several hours. Paltothyreus tarsatus is another termite-raiding species, with each individual stacking as many termites as possible in their mandibles before returning home while they recruit additional nestmates to the raiding site through chemical trails. The Malaysian basicerotine ant Eurhopalothrix heliscata uses a different strategy of termite hunting by pressing themselves into tight spaces, as they hunt through rotting wood housing termite colonies. Once inside, the ants seize their prey by using their short but sharp mandibles. Tetramorium uelense is a specialised predator species that feeds on small termites. A scout will recruit 10-30 workers to an area where termites are present, killing them by immobilising them with their stinger. Centromyrmex and Iridomyrmex colonies sometimes nest in termite mounds, and so the termites are regularly predated on by these ants; no evidence for any kind of relationship (other than a predatory one) is known. Other ants including Acanthostichus, Camponotus, Crematogaster, Cylindromyrmex, Leptogenys, Odontomachus, Ophthalmopone, Pachycondyla, Rhytidoponera, Solenopsis and Wasmannia prey on termites. In contrast to all these ant species, and despite their enormous diversity of prey, Dorylus ants rarely consume termites.
Ants are not the only invertebrates that perform raids. Many sphecoid wasps and several species including Polybia Lepeletier and Angiopolybia Araujo are known to raid termite mounds during the termites' nuptial flight.
Parasites, pathogens and viruses
As termites are usually well protected in their mounds and rarely consume invertebrates, termites are not ideal hosts for parasites; in comparison to bees and wasps, termites and ants are less likely to be attacked by parasites. Under imminent threat of an attack by parasites, a colony may migrate to a new location. However, fungi pathogens are major threats to a termite colony as they are not host-specific and may infect large portions of the colony; transmission usually occurs via direct physical contact. Termites are infected by a variety of parasites, including dipteran flies, Pyemotes mites, and fungi such as Aspergillus nomius and Metarhizium anisopliae. M. anispliae is known to weaken the termite immune system. Infection with A. nomius only occurs when a colony is under great stress. A large number of nematode parasites, most of which are in the order Rhabditida, also infect termites. Certain nematodes are an intermediate host; their final hosts are chickens. Other nematode parasites include those in the genus Mermis, Diplogaster aerivora and Harteria gallinarum. Inquilinism does not occur in the termite world.
Termites are infected by viruses including Entomopoxvirinae and the Nuclear Polyhedrosis Virus.
Locomotion and foraging
Both the worker and soldier caste lack wings and therefore never fly, and the reproductives only rely on their wings for a brief amount of time until they have found a suitable nest in which to mate, so termites are predominately reliant on their legs to move around. Chemicals such as acetamiprid can impair the locomotion of termites.
The foraging behaviour depends on the type of termite. For example, certain species feed on the wood structures they inhabit and others harvest food that is near the nest. Most workers do not forage unprotected and are rarely found out in the open; they rely on sheeting and runways to protect them from predators. Subterranean termites construct tunnels and galleries to look for food, and workers who manage to find food sources recruit additional nestmates by depositing a phagostimulant pheromone that attracts workers. When workers are foraging, communication among individuals is facilitated through the use of semiochemicals, and trail pheromones released from the sternal gland are laid down by workers who begin to forage outside of their nest. In one species, Nasutitermes costalis, there are three phases in a foraging expedition: first, soldiers scout an area. When they find a food source, they communicate to other soldiers and a small force of workers starts to emerge. In the second phase, workers appear in large numbers at the site. The third phase ends with a decrease in the number of soldiers present and an increase in the number of workers. Lévy flight behaviour may occur in isolated termite workers.
Competition
Competition between two colonies always results in agonistic behaviour towards each other, resulting in fights. These fights can cause mortality on both sides and, in some cases, the gain or loss of territory. "Cemetery pits" may be present, where the bodies of dead termites are buried. Studies show that, when termites encounter each other in foraging areas, some of the termites deliberately block passages to prevent other termites from entering. Dead termites from other colonies found in exploratory tunnels leads to the isolation of the area and thus the need to construct new tunnels. Conflict between two competitors does not always occur. For example, colonies of Macrotermes bellicosus and Macrotermes subhyalinus are not always aggressive towards each other though they might block each other's passages.
Suicide cramming is known in Coptotermes formosanus. Since C. formosanus colonies may get into physical conflict, some termites will tightly squeeze into foraging tunnels and die, successfully blocking the tunnel and ending all agonistic activities. Among the reproductive caste, neotenic queens may compete with each other to become the dominant queen when there are no primary reproductives. This struggle among the queens leads to the elimination of all but a single pair (a king and queen) that take over the colony. Ants and termites may compete with each other for nesting space. In particular, ants that prey on termites usually have a negative impact on arboreal nesting species.
Communication
Most termites are blind, so communication primarily occurs through chemical, mechanical and pheromonal cues. These methods of communication are used in a variety of activities, including foraging, locating reproductives, construction of nests, recognition of nestmates, nuptial flight, locating and fighting enemies, and defending the nests. The most common way of communicating is through antennation. Some species, such as Hodotermes mossambicus, have compound eyes which they use for orientation and to distinguish sunlight from moonlight. Due to this last ability, termites can forage during the day and night. Several species rely mainly on visual communication rather than on pheromones. A number of pheromones are known, including contact pheromones, which are transmitted when workers are engaged in trophallaxis or grooming, and alarm, trail and sex pheromones. The alarm pheromone and other defensive chemicals are secreted from the frontal gland; trail pheromones are secreted from the sternal gland. Sex pheromones derive from two glandular sources: the sternal and tergal glands. When termites go out to look for food, they forage in columns along the ground through vegetation. A trail can be identified by the faecal deposits or runways that are covered by objects. Workers leave pheromones on these trails, which are detected by other nestmates through olfactory receptors. Termites can also communicate through mechanical cues, vibrations, and physical contact. These signals are frequently used for alarm communication or for evaluating a food source.
Indirect communication is also known to exist in termite colonies. It is well known that when termites construct their nests, they communicate indirectly. Termites are not prompted to engage in building activity through direct communication. Instead, specific structures or other objects such as pellets of soil or pillars cause termites to start building. The termite adds these objects onto existing structures, and such behaviour encourages building behaviour in other workers. Termites can also distinguish nestmates and non-nestmates through chemical communication and gut symbionts: chemicals consisting of hydrocarbons released from the cuticle allow the recognition of alien termite species. Each colony has its own distinct odour. This odour is a result of genetic and environmental factors such as the termites' diet and the composition of the bacteria within the termites' intestines.
Defence
Termites rely on alarm communication to defend a colony. Alarm pheromones can be released when the nest has been breached or is being attacked by enemies or potential pathogens. Termites always avoid nestmates infected with Metarhizium anisopliae spores, through vibrational signals released by infected nestmates. Other methods of defence include intense jerking and secretion of fluids from the frontal gland and defecating faeces containing alarm pheromones.
A tunnel-blocking soldier can rebuff attacks from many ants. These tunnel-blocking soldiers are regarded as walking bombs, as the soldiers who block the tunnels explode as an act of defence and to block the tunnel. In cases where the intrusion is coming from a breach that is larger than the soldier's head, defence requires a special formations where soldiers form a phalanx-like formation around the breach and bite at intruders. If an invasion carried out by Megaponera analis is successful, an entire colony may be destroyed although this scenario is rare.
To termites, any breach of their tunnels or nests is a cause for alarm. When termites 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. Additionally, an alarmed termite will bump into other termites which cause them to be alarmed and leave pheromone trails to the disturbed area, which is also a way to recruit extra workers.
The pantropical subfamily Nasutitermitinae has a unique caste of soldiers, known as nasutes, that have the ability to exude noxious liquids through a horn-like nozzle frontal projection (nasus), that they use for defence. With this said, nasutes have lost their mandibles throughout the course of evolution. A wide variety of monoterpene hydrocarbons as solvents have been identified in the liquids nasutes secrete.
Soldiers of the species Globitermes sulphureus commit suicide by autothysis - rupturing a large gland just beneath the surface of their cuticles. The thick, yellow fluid in the gland becomes very sticky on contact with the air, entangling ants or other insects which are trying to invade the nest. Another termite, Neocapriterme taracua, also engages in suicidal defence. Workers physically unable to use their mandibles while in a fight form a pouch full of chemicals, and the workers deliberately rupture themselves, releasing toxic chemicals that paralyse and kill their enemies. The soldiers of the neotropical termite family Serritermitidae, have a defence strategy which involves front gland autothysis, with the body rupturing between the head and abdomen. Soldiers outside and attacked by intruders engage in autothysis when they are inside the nest entrance, denying entry to any attacker.
To avoid pathogens, termites occasionally engage in necrophoresis, in which a nestmate will carry away a corpse from the colony and dispose of it elsewhere. Instead, workers use other strategies to deal with their dead, including burying, cannibalism, and avoiding the corpse altogether. Which strategy is used depends on the nature of the corpse a worker is dealing with (i.e. the age of the carcass).
Relationship with other organisms
A species of fungus is known to mimic termite eggs, successfully avoiding its natural predators. These small brown balls, known as "termite balls", rarely kill the eggs, and in some cases the workers will even tend to them. This fungus mimics these eggs by producing a cellulose-digesting enzyme known as glucosidases. A unique mimicking behaviour exists between the beetle Trichopsenius frosti and the termite Reticulitermes flavipes. The beetle shares the same cuticle hydrocarbons as the termite and even biosynthesizes them. This chemical mimicry allows the beetle to integrate itself within the termite colony.
Some species of ant are known to enslave termites instead of killing them. For example, Formica nigra captures termites, and those who try to escape are immediately seized, driving them underground. Certain ants also conduct raids on termite colonies. Ants in the subfamily Ponerinae usually conduct these raids although other ants go in alone to steal the eggs or nymphs. Ants such as Megaponera analis attack termites while Dorylinae ants attack underground. Despite this, some termites and ants can coexist peacefully; some species, including Nasutitermes corniger, form associations with certain ant species to keep away predatory ant species. The earliest known association between Azteca ants and Nasutitermes termites date back to the Oligocene to Miocene period.
54 species of ants are known to inhabit Nasutitermes mounds, both occupied and abandoned ones. One reason many ants live in Nasutitermes mounds is due to the termites' frequent occurrence in their geographical range; another is to protect themselves from floods. Iridomyrmex also inhabits termite mounds although no evidence for any kind of relationship (other than a predatory one) is known. In rare cases, certain species of termites live inside active ant colonies. Some invertebrate organisms such as beetles, caterpillars, flies and millipedes are termitophiles and dwell inside termite colonies (they are unable to survive independently). Mounds may also provide shelter and warmth to birds, lizards, snakes and scorpions.
Termites are known to carry pollen and regularly visit flowers, so are regarded as potential pollinators for a number of flowering plants. One flower, in particular, Rhizanthella gardneri, is regularly pollinated by foraging workers, and it is perhaps the only Orchidaceae flower in the world to be pollinated by them.
Many plants have developed effective defences against termites. However, seedlings are completely vulnerable to termite attacks and need additional protection, as their defence mechanisms only develop when they have passed the seedling stage. Defence is typically achieved by secreting antifeedant chemicals into the woody cell walls. This reduces the ability of termites to efficiently digest the cellulose. A commercial product, "Blockaid", has been developed in Australia and uses a range of plant extracts to create a paint-on nontoxic termite barrier for buildings. In 2005, a group of Australian scientists announced a treatment based on an extract of a species of Eremophila that repels termites. Tests have shown that termites are strongly repelled by the toxic material to the extent that they will starve rather than consume cross treated samples. When kept close to the extract, they become disoriented and eventually die.
Nests
A termite colony is a structure that houses all individual termites. Normally, nests are composed of two parts, the inanimate and the animate. The animate is all of the termites living inside the colony, and the inanimate part is the structure itself, which is constructed by the termites. Nests only transform into mounds if the structure protrudes from the earth, and is made out of the soil. A nest has many functions such as providing a protected living space, retaining a stable climate within the colony and against predators. Most termites construct amorphous underground colonies, in comparison to multifunctional nests and mounds.
Termites primarily build their nests using faeces, which are good materials to use for construction. Other building material includes partly digested plant material, which creates carton nests (arboreal nests built from faecal elements and wood), and soil, which produces nests and mounds. Not all nests are visible, as many nests in tropical forests are located underground. Species in the subfamily Apicotermitinae are good examples, as they only dwell inside amorphous tunnels. Other termites live in wood, and tunnels are constructed as they feed on the wood. Nests and mounds also provide a fortification against predators, due to their extreme vulnerability. Nests made out of carton are particularly weak, and so the inhabitants use counter-attack strategies against invading predators.
Some species build complex nests called polycalic nests; this habitat is called polycalism. Polycalic species of termites form multiple nests, or calies, connected by subterranean chambers. The termite genera Apicotermes and Trinervitermes are known to have polycalic species. Polycalic nests appear to be less frequent in mound-building species although polycalic arboreal nests have been observed in a few species of Nasutitermes.
Mounds
Nests are only considered mounds if they protrude from the earth's surface. A mound provides termites the same protection as a nest but is stronger. Mounds located in areas with high rainfall are at risk of mound erosion; those made from carton can provide protection from the rain, and in fact can withstand high precipitation. Certain areas in mounds are used as strong points in case of a breach. For example, Cubitermes colonies build narrow tunnels used as strong points, as the diameter of the tunnels is small enough for soldiers to block. A highly protected chamber, known as the "queens cell", houses the queen and king and is used as a last line of defence.
Species in the genus Macrotermes arguably build the most complex structures in the insect world, constructing enormous mounds. These mounds are among the largest in the world, reaching a height of 8 to 9 metres (26 to 29 feet); they consist of chimneys, pinnacles and ridges. Another termite, Amitermes meridionalis, can build nests 3 to 4 metres (9 to 13 feet) high and 2.5 metres (8 feet) wide.
The sculptured mounds sometimes have elaborate and distinctive forms, such as those of the compass termite (Amitermes meridionalis and A. laurensis), which builds 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 narrow 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 above-ground mounds helps drive air circulation currents inside the subterranean network.
Shelter tubes
Termites construct shelter tubes, also known as earthen tubes, that start from the ground; they can be found on walls and other structures. Constructed by termites during the night due to higher humidity, these tubes provide protection to termites from potential predators, especially ants. Shelter tubes also provide high humidity and darkness and allow workers to collect food sources that cannot be accessed in any other way. These passageways are made from soil and faeces and are normally brown in colour; the size of these shelter tubes depends on the amount of food sources that are available. Normally, shelter tubes are less than a foot in height, but some tubes can exceed six feet.
Relationship with humans
As pests
Owing to their wood-eating habits, many termite species can do great damage to unprotected buildings and other wooden structures. Their habit of remaining concealed often results in their presence being undetected until the timbers are severely damaged, leaving a thin layer of a wall that protects them from the environment. Of the 3,106 species known, only 183 species cause damage; 83 species cause significant damage to wooden structures. In North America, nine subterranean species are pests; in Australia, 16 species have an economic impact; in the Indian subcontinent 26 species are considered pests, and in tropical Africa 24. In Central America and the West Indies, there are 17 pest species. Among the termite genera, Coptotermes has the highest number of pest species of any genus, with 28 species known to cause damage. Less than 10% of drywood termites are pests, but they infect wooden structures and furniture in tropical, subtropical and other regions. Dampwood termites only attack lumber material exposed to rainfall or soil. In April 2011, wood-eating termites were blamed for reportedly consuming more than $220,000 worth of Indian rupee notes.
Drywood termites thrive in warm climates, and human activities can enable them to invade homes since they can be transported through contaminated goods, containers and ships. It is possible that colonies can even thrive in warm buildings located in cold regions. Some termites are considered invasive species. Cryptotermes brevis is the most widely introduced invasive termite species in the world; it has been introduced to all the islands in the West Indies and to Australia.
In addition to causing damage to buildings, termites can also cause damage to food crops. Termites may attack trees if the trees' resistance to damage is low, but they generally ignore fast-growing plants. Most attacks occur when it is harvest time; crops and trees are attacked during the dry season or when they are still in the early stages of growth.
The damage caused by termites costs the southwestern United States approximately $1.5 billion each year in wood structure damage, but the true cost of damage worldwide cannot be determined. Drywood termites are responsible for a large proportion of the damage caused by termites. To better control the population of termites, researchers at the Agricultural Research Service have found a way to track the movement of the destructive pests. In 1990, researchers found a way to safely and reliably track termites using immunoglobulin G (IgG) marker proteins from rabbits or chickens. In field tests, termite bait was laced with the rabbit IgG, and the termites were randomly exposed to feeding on this bait. Termites were later collected from the field and tested for the rabbit-IgG markers using a rabbit-IgG-specific assay. However, this method of testing for the tracking proteins is expensive. Recently, researchers have developed a new way of tracking the termites using egg white, cow milk, or soy milk proteins, which can be sprayed on the termites in the field. This new method is less expensive because the proteins can be traced using a protein-specific ELISA test, which is more affordable because it is designed for mass production. Researchers hope to use this method of tracking termites to find a more cost-effective way of controlling the damaging pests.
As food
43 termite species are used in the human diet or in livestock feeding. These insects are particularly important in less developed countries where malnutrition is common, as the protein from termites can help improve the human diet. Termites are consumed in many regions globally, but this practice has only become popular in recent years. Researchers have suggested that termites are suitable candidates for human consumption in space.
Termites are consumed by people in many different cultures around the world; in Africa, the alates are an important factor in the diets of native populations. Tribes have different ways of collecting or cultivating insects; sometimes tribes will collect soldiers from several species. Queens are harder to acquire but are regarded as a delicacy if they can be collected. Termite alates are high in nutrition, with adequate levels of fat and protein, and are regarded as pleasant in taste, having a nut-like flavour after they are cooked.
Alates are collected when the rainy season begins. During a nuptial flight, they are typically seen around lights to which they are attracted, and so nets are set up on lamps and captured alates are later collected. The wings are removed through a technique that is similar to winnowing. The best result comes when they are lightly roasted on a hot plate or fried until crisp; oil is not required as their bodies usually contain sufficient amounts of oil. Termites are typically eaten when livestock is lean and tribal crops have not yet developed or produced any food, or if food stocks from a previous growing season are limited.
In addition to Africa, termites are consumed in local or tribal areas in Asia and North and South America. In Australia, Indigenous Australians are aware that termites are edible but do not consume them even in times of scarcity; there are few explanations as to why. Termites contribute to human nutrition via consumption of the soil, commonly known as geophagy. Termite mounds are the main sources of soil consumption in many countries including Kenya, Tanzania, Zambia, Zimbabwe and South Africa.
In agriculture and science
Termites can be major agricultural pests, particularly in East Africa and North Asia, where crop losses can be severe (3-100% in crop loss in Africa). Counterbalancing this is the greatly improved water infiltration where termite tunnels in the soil allow rainwater to soak in deeply and help reduce runoff and consequent soil erosion through bioturbation. In South America, cultivated plants such as eucalyptus, upland rice and sugarcane can be severely damaged by termite infestations, feeding on leaves, roots and woody tissue. Termites can also attack other plants, including cassava, coffee, cotton, fruit trees, maize, peanuts, soybeans and vegetables. Mounds can disrupt farming activities, making it difficult for farmers to operate farming machinery; despite this, some farmers only dislike their presence and no loss of production occurs. Termites can be beneficial to agriculture, by boosting crop yields and enriching the soil. Termites and ants can re-colonise untilled land that contains crop stubble, which colonies use for nourishment when they establish their nest. The presence of nests in fields enables larger amounts of rainwater to soak into the ground and increases the amount of nitrogen in the soil, both essential for the growth of crops.
Researchers at Harvard University have developed autonomous robots capable of constructing complex structures without human assistance, inspired by the complex mounds that termites build. These robots work independently and can move by themselves on a tracked grid, climb and lift up bricks. Such robots may be useful for future projects on the planet Mars, or to build levees to prevent flooding.
As an energy source
The U.S. Department of Energy is researching ways to eliminate the reliance on fossil fuels and replace it with cleaner energy, and the termite gut is helping researchers achieve this. The microbes in the termite gut manufactures substantial amounts of hydrogen; a single sheet of paper produces two litres of hydrogen when it is consumed by termites, making these insects an efficient bioreactor. The bacteria inside termites digest wood and plants and release the hydrogen that was trapped inside; termites achieve this high degree of efficiency by exploiting approximately 200 species of microbes inside their hindguts. The lignocellulose polymers break down into sugars from unidentified enzymes from the termite gut, and this process transforms the polymers into hydrogen. After this, the bacteria within the gut turns the sugar and hydrogen into cellulose acetate, an acetate ester of cellulose termites rely on for energy. Sequencing the termites microbes in the hindgut may provide a better understanding for the DOE to study the metabolic pathway. If the DOE can identify the enzymes that produce hydrogen, scientists may be able generate hydrogen using bioreactors from wood material and poplar that can be redistributed commercially.
In culture
The Eastgate Centre is a shopping centre and office block in central Harare, Zimbabwe, whose architect, Mick Pearce, used passive cooling inspired by that used by the local termites. Termite mounds include chimneys that vent through the top and sides, and the mound itself is designed to catch the breeze. As the wind blows, hot air from the main chambers below ground is drawn out of the structure, helped by termites opening or blocking tunnels to control air flow.
The Zoo Basel in Switzerland has two thriving Macrotermes bellicosus populations - resulting in an event very rare in captivity: the mass migrations of young flying termites. This happened in September 2008, when thousands of male termites left their mound each night, died, and covered the floors and water pits of the house holding their exhibit.
African tribes in several countries have termites as totems, and for this reason tribe members are forbidden to eat the reproductive alates. Termites are widely used in traditional popular medicine; they are used as treatments for diseases and other conditions such as asthma, bronchitis, hoarseness, influenza, sinusitis, tonsillitis and whooping cough. In Nigeria, Macrotermes nigeriensis is used for spiritual protection and to treat wounds and sick pregnant women. In Southeast Asia, termites are used in ritual practices. In Malaysia, Singapore and Thailand, termite mounds are commonly worshiped among the populace. Abandoned mounds are viewed as structures created by spirits, believing a local guardian dwells within the mound; this is known as Keramat and Datok Kong. In urban areas, local residents construct red-painted shrines over mounds that have been abandoned, where they pray for good health, protection and luck.
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