Termites

Termites belong to the Phylum Arthropoda, Class Insecta, Infraorder Isoptera, and Order Blattodea. They were formerly placed in a separate order (Isoptera) from the cockroaches (Blattodea), but Isoptera is currently classified at the taxonomic rank of infraorder. About 3,106 species are currently described within twelve families, with a few hundred more to still be described. There are several species of termites in Arkansas.

Termites are among the most successful groups of insects on Earth, colonizing all continents except Antarctica. Comparatively speaking, the diversity of termite species is rather low in North America and Europe (fifty species are known from North America, and only ten species occur in Europe), but it is higher in South America, where over 400 species are recognized. Of the species currently classified, about a third (1,000) occur in Africa. In Asia, there are 435 species, which are mainly distributed in China, where they are restricted to mild tropical and subtropical habitats south of the Yangtze River. In Australia, all ecological groups of termites are endemic to the continent, with over 360 classified species. In North America, termites (genus Zootermopsis) are found as far north as Vancouver, British Columbia, Canada, on the Pacific coast, and Maine and eastern Canada (genus Reticulitermes) on the Atlantic coast.

Recent phylogenetic studies indicate that termites evolved from cockroaches during the Jurassic or Triassic. However, the first termites possibly emerged during the Permian or perhaps even the Carboniferous. The oldest unmistakable 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, they likely originated earlier in the Jurassic or Triassic. Termites were the first social insects to evolve a caste system, more than 100 million years ago. The oldest termite nest discovered is believed to be from the Upper Cretaceous in west Texas, where the oldest known fecal pellets were also discovered. A giant termite, the extinct Gyatermes styriensis, flourished in Austria during the Miocene and had a wingspan of 76 mm (3.0 in.) and a body length of 25 mm (0.98 in.).

A robust DNA analysis using 16S rRNA sequences published in 2008 supported the position of termites being nested within the evolutionary tree containing the order Blattodea, which included the cockroaches. The wood cockroach genus Cryptocercus is considered to be a sister-group to them, as it shares the strongest phylogenetical similarity with termites. Therefore, termites are thought to be the descendants of the genus Cryptocercus. Termites and Cryptocercus also share similar morphological and social behavioral features. For example, most cockroaches do not exhibit social characteristics, but Cryptocercus takes care of its young and exhibits other social behavior such as trophallaxis and allogrooming. It has been proposed that the Isoptera and Cryptocercidae be grouped in the clade “Xylophagodea.” Some taxonomists have also suggested a more conservative approach by retaining the termites as the Termitoidae, an epifamily within the cockroach order, which preserves the classification of termites at the family level and below. Termites have long been accepted to be closely related to cockroaches and mantids, and they are classified in the same superorder (Dictyoptera).

Because they possess soft cuticles, termites do not generally inhabit cool or cold habitats. There are three ecological groups of termites: (1) dampwood, (2) drywood, and (3) subterranean. Dampwood species are found only in coniferous forests, whereas drywood termites are found in hardwood forests; subterranean termites live in more widely diverse areas. One species in the drywood group is the West Indian drywood termite (Cryptotermes brevis), which is an invasive species in Australia.

Compared to most other insects, termites are usually minute, measuring between four and fifteen mm (0.16 to 0.59 in.) in length. The largest of all extant termites are the queens of the African mound-building termite, Macrotermes bellicosus, measuring over 100 mm (3.9 in.) in length.

Most worker and soldier termites are completely blind, as they do not possess eyes. However, some species, such as the African harvester termite (Hodotermes mossambicus), have compound eyes they use for orientation and to distinguish sunlight from moonlight. The alates (winged males and females) possess eyes along with lateral ocelli. Lateral ocelli, however, are not found in all termites, including three families (Hodotermitidae, Termopsidae, and Archotermopsidae).

Like other insects, termites have a small tongue-shaped labrum and a clypeus; the clypeus is divided into a postclypeus and an anteclypeus. The mouth parts also contain a maxillae and a set of mandibles. The maxillae and labium have palps that help individuals sense food and handling. There are three basic segments of a termite antenna; they include a scape, a pedicel (typically shorter than the scape), and all segments beyond the scape and pedicel, the flagellum. These antennae have various functions such as the sensing of heat, taste, odors (including pheromones), touch, and vibration. In harmony with all other insects, the anatomy of the termite thorax consists of three segments (and each contains a pair of legs): (1) the prothorax, (2) the mesothorax, and (3) the metathorax. On alates, the wings are located at the mesothorax and metathorax. The mesothorax and metathorax have well-developed exoskeletal plates; the prothorax has smaller plates. Termites have a ten-segmented abdomen with two plates, the tergites and the sternites. The tenth abdominal segment has a pair of short cerci. There are ten tergites, of which one is elongated and nine are wide. The structure of the legs is consistent with other insects: the parts include a coxa, trochanter, femur, tibia (with spurs), and tarsus. The number of tibial spurs on an individual’s leg varies. Some species of termites possess an arolium, located between the claws, which is present in species that climb on smooth surfaces but is absent in most other termites.

Like ants and some other hymenopterans (bees and wasps), termites divide labor among castes consisting of male and female “workers” and “soldiers” that are usually sterile. Worker termites, which constitute the majority in a colony, are diploid individuals that develop from fertilized eggs. Workers may be either sex but are usually sterile, especially in populations that have a nest site that is separate from their foraging site. Sterile workers are sometimes called “true workers,” while those that are fertile, as in the wood-nesting dampwood termites, Termopsidae (Archotermopsidae), are termed as “false workers.” The most labor within the colony is undertaken by worker termites, being responsible for foraging, food storage, and brood and nest maintenance. They are responsible for the digestion of cellulose and are thus the most likely caste to be found associated with infested wood. Trophallaxis is the process of worker termites feeding other nest mates and is an effective nutritional tactic to convert and recycle nitrogenous components. It exempts the parents from feeding all but the first generation of offspring, allowing for the group to become much larger and guaranteeing that the necessary digestive symbionts are transferred from one generation to another. Some termite species sometimes rely on nymphs to perform work without differentiating them as a separate caste.

The sole purpose of the soldier caste is to defend the colony, as they possess anatomical and behavioral specializations for it. Many have huge heads with highly modified powerful jaws so big that they cannot feed themselves. Instead, similar to juveniles, they are fed by workers. A feature of the subterranean wood termites (family Rhinotermitidae) are simple holes in the forehead that exude defensive secretions (fontanelles). Many species are readily taxonomically identified using the characteristics of the soldiers’ larger and darker head and large mandibles. Soldiers among certain termites may use their globular (phragmotic) heads to block their narrow tunnels. Different types of soldiers include minor and major soldiers, and highly modified soldiers called nasutes of the pantropical subfamily Nasutitermitinae possess a horn-like nozzle frontal projection (nasus). These unique soldiers are capable of spraying noxious, sticky secretions containing diterpenes (oily monoterpene hydrocarbons) at their enemies. Nitrogen fixation plays an important role in nasute nutrition. Soldiers are usually sterile, but some species of Archotermopsidae are known to include neotenic forms with soldier-like heads while also having reproductive organs.

The reproductive caste of a mature colony includes a fertile female and male (drone), known as the queen and king, respectively. Males are haploid (1N) and develop from unfertilized eggs, while the females (both workers and the queen) are diploid (2N) and develop from fertilized eggs. The primary queen of the colony is strictly responsible for egg production for the colony and has a great capacity to lay eggs. In the very early stages of the colony, the queen only lays about ten to twenty eggs but is capable of laying as many as 1,000 per day when the colony is several years old. Queens have the longest lifespan of any insect in the world, with some documented as living thirty to fifty years. Unlike in ants, the king mates with the queen for life. In some species, the queen’s abdomen distends dramatically to increase fecundity, a reproductive characteristic referred to as physogastrism; when this occurs, queens may produce 40,000 eggs a day. Also, depending on the species, the queen begins to produce reproductive winged alates at certain times of the year, and when nuptial flight begins, huge swarms emerge from the colony. However, these swarms attract a wide variety of predators and many are eaten.

Unlike ants, which undergo a complete metamorphosis, each individual termite goes through an incomplete metamorphosis that proceeds through egg, nymph, and adult stages. The number of termites in a colony varies, with the larger species typically having 100 to 1,000 individuals. However, some termite colonies, including those with larger individuals, can number in the millions.

The life cycle begins with an egg that goes through a sequential developmental process. In the next stage, nymphs resemble small adults, and go through a series of molts as they develop. In some species, eggs go through four molts, whereas nymphs go through three. Nymphs first molt into workers, and then some workers go through further molting to become soldiers or alates; workers become alates only by molting into alate nymphs. The development from nymph to adult can take months depending 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 such as foraging, building, or maintaining the nest or tending to the queen. Pheromones regulate the caste system in termite colonies, preventing all but a very few of the termites from becoming fertile queens.

The reproductive organs are more basic but still similar to those in cockroaches. For example, the intromittent organ (organ of copulation) is not present in male alates, and the sperm is either immotile or aflagellate. However, some termites (Mastotermitidae) have multiflagellate sperm with restricted motility. The genitalia of females are also streamlined, with paired mature ovaries that may have some 2,000 ovarioles each. Unlike most other termites, females of Mastotermitidae possess an ovipositor, a feature strikingly akin to that in cockroach females. The primitive giant northern or Darwin termite (Mastotermes darwiniensis) displays numerous cockroach-like reproductive and morphological characteristics that are not shared with other termites, such as laying its eggs in rafts and having anal lobes on the wings.

The non-reproductive castes of termites are wingless and rely exclusively on their six legs for movement, including alates that fly only for a brief amount of time. The morphology of the legs is similar in each caste; however, the soldiers have larger and heavier legs. Unlike in ants, the hindwings and forewings are of equal length. For the bulk of time, the alates are poor flyers; however, they use a special method to launch themselves in the air and fly in a random direction. Research has shown that in comparison to larger termites, smaller termites cannot fly long distances. When a termite is flying, its wings remain at a right angle, and when at rest, its wings remain parallel to the body.

Termites are placed into two groups (the lower termites and the higher termites) depending on their feeding habits. The lower termites predominately eat wood (the polysaccharide cellulose). They possess a specialized midgut that breaks down the fiber. Because wood is hard for them to digest, termites prefer to also consume fungus-infected wood because it is simpler to process and the fungi are high in protein. On the other hand, higher termites consume a wide variety of materials, including animal feces, humus, grass, leaves, and roots. The gut in the lower termites contains many species of bacteria along with Protista, while the higher termites only have a few species of bacteria with no protistans. In subtropical and tropical regions, termites are particularly important, as they recycle waste material such as wood and plant matter that is of considerable ecological importance. Certain species, such as a desert termite (Gnathamitermes tubiformans), have seasonal food habits. For example, they may preferentially consume red three-awn (Aristida longiseta) during the summer, buffalograss (Buchloe dactyloides) from May to August, and blue grama (Bouteloua gracilis) during spring, summer, and autumn. Interestingly, colonies of G. tubiformans consume less food in spring than they do during autumn.

Termite nests equate to mounds if they protrude from the earth’s surface. The mound provides termites the same protection as a nest but is stronger. Those located in regions with continuous and torrential rainfall are at risk of erosion due to their clay-rich construction. Species in the Old World genus Macrotermes unquestionably build the most multifaceted structures of all the insects, constructing enormous mounds. These mounds are among the largest on Earth, reaching a height of 8 to 9 m (26 to 29 ft.) and consisting of chimneys, pinnacles, and ridges. Another termite species, the endemic magnetic or compass termite of northern Australia, Amitermes meridionalis, can build nests 3 to 4 m (9 to 13 ft.) high and 2.5 m (8 ft.) wide. The tallest termite mound ever found was in Democratic Republic of the Congo and measured 12.8 m (42 ft.) long.

In the diet of some human cultures, termites are considered a delicacy and are sometimes used in traditional medicines. Forty-three species are used as food by humans or are fed to livestock. These insects are particularly important in third-world countries where malnutrition is common, as the protein from termites can help improve the human diet. In many parts of Africa, for example, the alates collected when the rainy season begins are an important factor in the diets of native populations, as they are high in nutrition with adequate levels of fat and protein. Though more difficult to obtain, queens are regarded as a delicacy, as they are viewed as more pleasant in taste, having a nutty flavor after they are cooked. In addition to Africa, termites are consumed in local or tribal areas of Asia and North and South America. In traditional medicine, they have been used as treatments for conditions such as asthma, bronchitis, hoarseness, influenza, sinusitis, tonsillitis, and whooping cough.

Outside of humans, termites are consumed by a wide variety of predators. A food habits study found remains of one species alone, the African harvester termite, Hodotermes mossambicus, in the stomach contents of sixty-five birds and nineteen mammals. Arthropods such as ants, centipedes, cockroaches, crickets, dragonflies, scorpions, and spiders; reptiles such as lizards; and amphibians such as frogs and toads eat termites. There are also two spiders in the termite-hunter family Ammoxenidae that are specialists on termites. Mammalian predators include aardvarks, aardwolves, anteaters, bats, bears, bilbies, foxes, galagos, numbats, mice, pangolins, and spiny echidnas. One of these, the aardwolf (Proteles cristata) is an insectivorous mammal that primarily feeds on termites; it locates its food by detecting the scent secreted by the soldiers and also by their sound. By using its long, sticky tongue, one aardwolf is capable of consuming thousands of termites in a single evening. In addition, sloth bears (Melursus ursinus) of the Indian subcontinent can break open mounds to consume the nest mates, while chimpanzees (Pan troglodytes) have developed specialized tools to pluck termites from their nest. Analysis of bone tools used by the early hominin, Paranthropus (Australopithecus) robustus, first discovered in 1938 in southern Africa, suggests they used these tools to excavate termite mounds.

Among all termite predators, however, ants are the greatest nemesis, and some genera are specialist predators (termitophagous) of termites. For example, Megaponera of sub-Saharan Africa is a strictly termite-eating genus that performs pillaging activities, some lasting several hours. Another termite-raiding species, the African stink ant (Paltothyreus tarsatus), individually stacks as many termites as possible in its mandibles before coming back to its home. The Malaysian basicerotine ant (Eurhopalothrix heliscata) uses a different line of attack when hunting as they search through rotting wood housing termite colonies by pressing themselves into tight spaces. Once inside, the ants grab hold of their prey by using their short but sharp mandibles. Tetramorium uelense of Africa is a specialized predator species that feeds on small termites by scouting ten to thirty worker ants to an area where termites are present, immobilizing and killing them with their stinger. Two colonies of ant genera, the Afrotropical Centromyrmex and rainbow ant (Iridomyrmex), sometimes nest in termite mounds; therefore, the termites are preyed on by these ants. Other ant genera also prey on termites, including Acanthostichus, Camponotus, Crematogaster, Cylindromyrmex, Leptogenys, Odontomachus, Ophthalmopone, Pachycondyla, Rhytidoponera, Solenopsis, and Wasmannia. Interestingly, ants are not the only arthropods that perform raids. For example, many sphecoid wasps and several other species including eusocial wasps (Polybia) of Central and South America and Neotropical social wasps (Angiopolybia) are known to break into termite mounds during the termites’ nuptial flights.

Termites are believed to be a major source (up to 11 percent) of one of the prime greenhouse gases (atmospheric methane), produced from the metabolic breakdown of cellulose. Termites rely primarily upon symbiotic (mutualistic) protistans (metamonads) and other microbes such as flagellates in their guts to digest the cellulose for them, allowing them to absorb the metabolic end products for their own use. Hindgut protists, in turn, such as anaerobic parabasalians (Trichonympha), rely on symbiotic bacteria embedded on their surfaces to produce some of the necessary digestive enzymes. Many higher-level termites, especially those within the most advanced family (Termitidae), rely primarily upon bacteria but can produce their own cellulase enzymes. All of the workers feed the other members of the colony with substances derived from the digestion of plant material, either from the mouth or anus.

Some species of termites exercise fungus farming (fungiculture) by maintaining a “garden” of specialized fungi (Termitomyces), which are nourished by their fecal material. Once the fungi are consumed, their spores proceed undamaged through the digestive tract of the termites to complete the cycle by germinating in the fresh fecal pellets. It is assumed that more than 90 percent of dry wood in the semiarid savannah ecosystems of Asia and Africa are reprocessed by Macrotermitinae termites.

As pests, because of their wood-eating habits, many termite species can do substantial damage to unprotected buildings and other wooden structures. Several hundred species are economically significant as pests that can cause serious damage to buildings, crops, or plantation forests. The conflict with humans occurs where structures and landscapes containing structural wood components, cellulose-derived structural materials, and ornamental vegetation provide termites with a reliable source of food and moisture. Their habit of remaining concealed often results in their presence being very difficult to detect until the timbers are severely damaged, with only a thin exterior layer of wood remaining. This damage can be very expensive to repair. A failed termite inspection of a residence can be potentially costly to a homeowner who is trying to sell a house. Of the 3,106 species known, only 183 (6 percent) species cause damage; eighty-three of these species cause significant damage to wooden structures. Among genera, the Asian subterranean termite, Coptotermes, has the highest number of pest species of any genus, with twenty-eight species known to cause destruction. In addition to causing damage to buildings, termites can be major agricultural pests that damage food crops. In East Africa and North Asia, crop losses can be severe. The damage caused by termites costs the southwestern United States approximately $1.5 billion each year in wood structure damage, but the absolute cost of damage worldwide is difficult to determine.

In terms of parasites, termites are less likely to be infected by parasites than hymenopterans, as they are usually well protected in their mounds. However, termites are infected/infested by a variety of parasites, including flies (Diptera), mites (Pyemotes), and a large number of nematodes (order Rhabditida). Pathogenic fungi transmitted via direct physical contact such as Aspergillus nomius and Metarhizium anisopliae are major threats to a termite colony, as they are not host-specific and may infect large portions of the colony. Infection with the latter fungus only occurs when a colony is under great stress and has been reported to weaken the termite immune system. Some viruses infect termites, including Entomopoxvirinae and the Nuclear Polyhedrosis Virus. In an attempt to avoid pathogens, termites occasionally engage in necrophoresis, in which a nest mate carries away a corpse from the colony to dispose of it elsewhere.

In Arkansas, four species of termites were reported from a 1954 publication in the state, including Reticulitermes flavipes, R. hageni, R. tibialis, and R. virginicus. In addition, the genetic diversity of Reticulitermes termites (Rhinotermitidae) was studied from specimens collected from Lake Wedington (Washington County). In a 2004 study of specimens collected from thirty-five Arkansas counties, a total of fifty-nine R. flavipes, thirteen R. hageni, and seven R. virginicus haplotypes were identified. In Arkansas alone, eleven mitochondrial haplotypes were observed in R. flavipes, three in R. hageni, and three in R. virginicus. In a more recent study, investigators used genetic methods to characterize the breeding structure of three species of Reticulitermes from three sites of northwestern Arkansas (Lake Wedington, Lee Creek area in Crawford County, and the University of Arkansas Agricultural Research and Extension Center in Fayetteville in Washington County) and compared two habitats: undeveloped, forested sites and developed, agricultural sites.

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Chris T. McAllister
Eastern Oklahoma State College