Antelope

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An antelope is a member of a number of even-toed ungulate species indigenous to various regions in Africa and Eurasia. Antelopes comprise a wastebasket taxon (miscellaneous group) within the family Bovidae, encompassing those Old World species that are neithercattle, sheep, buffalo, bison, nor goats. A herd of antelope is called a herd.

Etymology

The English word "antelope" first appeared in 1417 and is derived from the Old French antelop, itself derived from Medieval Latinant(h)alopus, which in turn comes from the Byzantine Greek word anthólops, first attested in Eustathius of Antioch (circa 336), according to whom it was a fabulous animal "haunting the banks of the Euphrates, very savage, hard to catch and having long, saw-like horns capable of cutting down trees".^[2] It perhaps derives from Greek anthos (flower) and ops (eye), perhaps meaning "beautiful eye" or alluding to the animals' long eyelashes. This, however, may be a later folk etymology. The word talopus and calopus, from Latin, came to be used in heraldry. In 1607, it was first used for living, cervine animals.

Species

The 91 species, most of which are native to Africa, occur in about 30 genera. The classification of tribes or subfamilies within Bovidae is still a matter of debate, with several alternative systems proposed.

Antelope are not a cladistic or taxonomically defined group. The term is used to describe all members of the family Bovidae that do not fall under the category of sheep, cattle, orgoats. Usually, all species of the Alcelaphinae, Antilopinae, Hippotraginae, Reduncinae, Cephalophinae, many Bovinae, the grey rhebok, and the impala are called antelopes.

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Distribution and habitat

No antelope species is native to Australasia or Antarctica, nor do any extant species occur in the Americas, though the nominate saiga subspecies occurred in North America during the Pleistocene. North America is currently home to the native pronghorn, which is not officially recognized as an antelope, but locally referred to as such (e.g. Antelope Valley).

More species of antelope are native to Africa than to any other continent, but some occur in Asia. The Arabian Peninsula is home to the Arabian oryx and Dorcas gazelle. India is home to the nilgai, chinkara, blackbuck, Tibetan antelope, and four-horned antelope, while Russia and Central Asia have the Tibetan antelope, and saiga.

Many species of antelopes have been imported to other parts of the world, especially the United States, for exotic game hunting. With some species possessing spectacular leaping and evasive skills, individuals may escape. Texas in particular has many game ranches, as well as habitats and climates, that are very hospitable to African and Asian plains antelope species. Accordingly, wild populations of blackbuck antelope, gemsbok, and nilgai may be found in Texas.^[3]

Antelope live in a wide range of habitats. Numerically, most live in the African savannahs. However, many species are more secluded, such as the forest antelope, as well as the extreme cold-living saiga, the desert-adapted Arabian oryx, the rocky koppie-living klipspringer, and semiaquatic sitatunga.^[4]

Species living in forests, woodland, or bush tend to be sedentary, but many of the plains species undertake long migrations. These enable grass-eating species to follow the rains and thereby their food supply. The gnus and gazelles of East Africa perform some of the most impressive mass migratory circuits of all mammals.

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Morphology

For example, a male common eland can measure 178 cm (70 in) at the shoulder and weigh almost 950 kg (2,090 lb), whereas an adultroyal antelope may stand only 24 cm (9.4 in) at the shoulder and weigh a mere 1.5 kg (3.3 lb).

Not surprisingly for animals with long, slender yet powerful legs, many antelopes have long strides and can run fast. Some (e.g. klipspringer) are also adapted to inhabiting rock koppies and crags. Both dibatags and gerenuks habitually stand on their two hind legs to reach acacia and other tree foliage. Different antelope have different body types, which can affect movement. Duikers are short, bush-dwelling antelope that can pick through dense foliage and dive into the shadows rapidly. Gazelles and springbok are known for their speed and leaping abilities. Even larger antelope, such as nilgai, elands, and kudus, are capable of jumping 2.4 m (7.9 ft) or greater, although their running speed is restricted by their greater mass.

Antelope have a wide variety of coverings, though most have a dense coat of short fur. In most species, the coat (pelage) is some variation of a brown colour (or several shades of brown), often with white or pale underbodies. Exceptions include the zebra-marked zebra duiker, the grey, black, and white Jentink's duiker, and the black lechwe. Most of the "spiral-horned" antelopes have pale, vertical stripes on their backs. Many desert and semidesert species are particularly pale, some almost silvery or whitish (e.g. Arabian oryx); the beisa andsouthern oryxes have gray and black pelages with vivid black-and-white faces. Common features of various gazelles are white rumps, which flash a warning to others when they run from danger, and dark stripes midbody (the latter feature is also shared by the springbok and beira). The springbok also has a pouch of white, brushlike hairs running along its back, which opens up when the animal senses danger, causing the dorsal hairs to stand on end.

Antelope are ruminants, so have well-developed molar teeth, which grind cud (food balls stored in the stomach) into a pulp for further digestion. They have no upper incisors, but rather a hard upper gum pad, against which their lower incisors bite to tear grass stems and leaves.

Like many other herbivores, antelopes rely on keen senses to avoid predators. Their eyes are placed on the sides of their heads, giving them a broad radius of vision with minimal binocular vision. Their horizontally elongated pupils also help in this respect. Acute senses of smell and hearing give antelope the ability to perceive danger at night out in the open (when predators are often on the prowl). These same senses play an important role in contact between individuals of the same species; markings on their heads, ears, legs, and rumps are used in such communication. Many species "flash" such markings, as well as their tails; vocal communications include loud barks, whistles, "moos", and trumpeting; many species also use scent marking to define their territories or simply to maintain contact with their relatives and neighbors.

Many antelope are sexually dimorphic. In most species, both sexes have horns, but those of males tend to be larger. Males tend to be larger than the females, but exceptions in which the females tend to be heavier than the males include the bush duiker, dwarf antelope, Cape grysbok, and oribi, all rather small species. A number of species have hornless females (e.g. sitatunga, red lechwe, and suni). In some species, the males and females have differently coloured pelages (e.g. blackbuck and nyala).

Horns are efficient weapons, and tend to be better developed in those species where males fight over females (large herd antelope) than in solitary or lekking species. With male-male competition for mates, horns are clashed in combat. Males more commonly use their horns against each other than against another species. The boss of the horns is typically arranged in such a way that two antelope striking at each other's horns cannot crack each other's skulls, making a fight via horn more ritualized than dangerous. Many species have ridges in their horns for at least two-thirds the length of their horns, but these ridges are not a direct indicator of age.The size and shape of antelope horns varies greatly. Those of the duikers and dwarf antelopes tend to be simple "spikes", but differ in the angle to the head from backward curved and backward pointing (e.g. yellow-backed duiker) to straight and upright (e.g. steenbok). Other groups have twisted (e.g. common eland), spiral (e.g. greater kudu), "recurved" (e.g. the reedbucks), lyrate (e.g. impala), or long, curved (e.g. the oryxes) horns. Horns are not shed and their bony cores are covered with a thick, persistent sheath of horny material, both of which distinguish them from antlers.

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Behavior

§Mating strategies

Small antelope, such as dik-diks, tend to be monogamous. They live in a forest environment with patchy resources, and a male is unable to monopolize more than one female due to this sparse distribution. Larger forest species often form very small herds of two to four females and one male.Antelope are often classified by their reproductive behavior.

Some species, such as lechwes, pursue a lek breeding system, where the males gather on a lekking ground and compete for a small territory, while the females appraise males and choose one with which to mate.

Large grazing antelope, such as impala or wildebeest, form large herds made up of many females and a single breeding male, which excludes all other males, often by combat.

§Defense

Large antelope that gather in large herds, such as wildebeest, rely on numbers and running speed for protection. In some species, adults will encircle the offspring, protecting them from predators when threatened. Many forest antelope rely on cryptic coloring and good hearing to avoid predators. Forest antelope often have very large ears and dark or striped colorations. Small antelope, especially duikers, evade predation by jumping into dense bush where the predator cannot pursue.^[7] Springboks use a behavior known as stotting to confuse predators.Antelope pursue a number of defense strategies, often dictated by their morphology.

Open grassland species have no where to hide from predators, so they tend to be fast runners. They are agile and have good endurance—these are advantages when pursued by sprint-dependent predators such as cheetahs, which are the fastest of land animals, but tire quickly. Reaction distances vary with predator species and behaviour. For example, gazelles may not flee from a lion until it is closer than 200 m (650 ft)—lions hunt as a pride or by surprise, usually by stalking; one that can be seen clearly is unlikely to attack. However, sprint-dependent cheetahs will cause gazelles to flee at a range of over 800 m (0.5 mile).

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Status

About 25 species are rated by the IUCN as endangered, such as the dama gazelle and mountain nyala. A number of subspecies are also endangered, including the giant sable antelope and the mhorr gazelle. The main causes for concern for these species are habitat loss, competition with cattle for grazing, and trophy hunting.

The chiru or Tibetan antelope is hunted for its pelt, which is used in making shahtoosh, an incredibly fine material used in shawls. Since the fur can only be removed from dead animals, and each animal yields very little of the downy fur, several antelope must be killed to make a single shawl. This unsustainable demand has led to enormous declines in the chiru population.

The saiga is hunted for its horns, which are considered an aphrodisiac by some cultures. Only the males have horns, and have been so heavily hunted that some herds contain up to 800 females to one male. The species has shown a steep decline and is critically endangered.

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Lifespan

It is difficult to determine how long antelope live in the wild. With the preference of predators towards old and infirm individuals, which can no longer sustain peak speeds, few wild prey-animals live as long as their biological potential. In captivity, wildebeest have lived beyond 20 years old, and impalas have reached their late teens. ^[10]

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Humans

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Culture

The antelope's horn is prized for medicinal and magical powers in many places. The horn of the male saiga, in Eastern practice, is ground as an aphrodisiac, for which it has been hunted nearly to extinction.^[11] In the Congo, it is thought to confine spirits. Christian iconography sometimes uses the antelope's two horns as a symbol of the two spiritual weapons Christians possess: the Old Testament and the New Testament. The antelope's ability to run swiftly has also led to their association with the wind, such as in the Rig Veda, as the steeds of theMaruts and the wind god Vayu. There is, however, no scientific evidence that the horns of any antelope have any change on a human's physiology or characteristics.

Domestication

Domestication of animals requires certain traits in the animal that antelope do not typically display. Most species are difficult to contain in any density, due to the territoriality of the males, or in the case of oryxes (which have a relatively hierarchical social structure), an aggressive disposition; they can easily kill a human. Because many have extremely good jumping abilities, providing adequate fencing is a challenge. Also, antelope will consistently display a fear response to perceived predators, such as humans, making them very difficult to herd or handle. Although antelope have diets and rapid growth rates highly suitable for domestication, this tendency to panic and their nonhierarchical social structure explains why farm-raised antelope are uncommon. Ancient Egyptians kept herds of gazelles and addax for meat, and occasionally pets. It is unknown whether they were truly domesticated, but it seems unlikely, as no domesticated gazelles exist today.

However, humans have had success taming certain species, such as the elands. These antelope sometimes jump over each other's backs when alarmed, but this incongruous talent seems to be exploited only by wild members of the species; tame elands do not take advantage of it and can be enclosed within a very low fence. Their meat, milk, and hides are all of excellent quality, and experimental eland husbandry has been going on for some years in both the Ukraine and Zimbabwe. In both locations, the animal has proved wholly amenable to domestication.^[12] Similarly, European visitors to Arabia reported “tame gazelles are very common in the Asiatic countries of which the species is a native; and the poetry of these countries abounds in allusions both to the beauty and the gentleness of the gazelle.”^[13] Other antelope that have been tamed successfully include the gemsbok,^[14] the kudu,^[15] and the springbok.^[15] Nor are the characteristics described above necessarily barriers to domestication; for further information, see animal domestication.

Anteater

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Anteater is a common name for the four extant mammal species of the suborder Vermilingua(meaning "worm tongue") commonly known for eating ants and termites.^[2] The individual species have other names in English and other languages. Together with the sloths, they are within the order Pilosa. The name "anteater" is also colloquially applied to the unrelated aardvark, numbat, echidnas, pangolinsand some members of the Oecobiidae.

Physical characteristics

All anteaters have elongated snouts equipped with a thin tongue that can be extended to a length greater than the length of the head; their tube-shaped mouths have lips but no teeth. They use their large, curved foreclaws to tear open ant and termite mounds and for defense, while their dense and long fur protects them from attacks from the insects. All species except the giant anteater have a longprehensile tail. 

Behaviour

Anteaters have a poor sense of sight, but an excellent sense of smell, and most species depend on the latter for foraging, feeding, and defence. Their sense of hearing is thought to be good. ^[6]Anteaters are mostly solitary mammals prepared to defend their 1.0- to 1.5-mi² (2.6- to 2.9-km²) territories. Normally, they do not enter a territory of another anteater of the same sex, but males often enter the territory of associated females. When a territorial dispute occurs, they vocalize, swat, and can sometimes sit on or even ride the back of their opponents. 

With a body temperature fluctuating between 33 and 36 °C (91 and 97 °F), anteaters, like other xenarthrans, have among the lowest body temperatures of any mammal,^[7] and can tolerate greater fluctuations in body temperature than most mammals. Its daily energy intake from food is only slightly greater than its energy need for daily activities, and anteaters probably coordinate their body temperatures so they keep cool during periods of rest, and heat up during foraging. 

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Reproduction

Adult males are slightly larger and more muscular than females, and have wider heads and necks. Visual sex determination can, however, be difficult, since the penis and testes are located internally between the rectum and urinary bladder in males and females have a single pair of mammae near the armpits. Fertilization occurs by contact transfer without intromission, similar to some lizards. Polygynous mating usually results in a single offspring; twins are possible but rare. The large foreclaws prevent mothers from grasping their newborns and they therefore have to carry the offspring until they are self-sufficient. 

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Feeding

Anteaters are specialized to feed on ants, termites and sometimes spiders, each anteater species having its own insect preferences: small species are specialized on arboreal insects living on small branches, while large species can penetrate the hard covering of the nests of terrestrial insects. To avoid the jaws, sting, and other defences of the invertebrates, anteaters have adopted the feeding strategy to lick up many ants and termites as quickly as possible — an anteater normally spends about a minute at a nest before moving on to another — and a giant anteater has to visit up to 200 nests to consume the thousands of insects it needs to satisfy its caloric requirements. 

The anteater's tongue is covered with thousands of tiny hooks called filiform papillae which are used to hold the insects together with large amounts of saliva. Swallowing and the movement of the tongue are aided by side-to-side movements of the jaws. The anteater's stomach, similar to a bird's gizzard, has hardened folds and uses strong contractions to grind the insects; a digestive process assisted by small amounts of ingested sand and dirt.  The tongue is attached to the sternum and moves very quickly, flicking 150 times per minute.

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Distribution

Silky anteaters and northern tamanduas extend their ranges as far north as southeastern Mexico, while giant anteaters can be found as far north as Central America. Southern tamanduas range south to Uruguay (giant anteaters did also until their recent extirpation there) and the ranges of all species except the northern tamandua overlap in eastern Brazil Anteaters were confined to South America, which was formerly an island continent, during most of the Cenozoic Era. Once the Isthmus of Panama formed about three million years ago, however, anteaters invaded Central America as part of the Great American Interchange.

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Habitat

Anteater habitats includes dry tropical forests, rainforests, grasslands, and savannas. The silky anteater (Cyclopes didactylus) is specialized to an arboreal environment, but the more opportunistic tamanduas find their food both on the ground and in trees, typically in dry forests near streams and lakes. The almost entirely terrestrial giant anteater (Myrmecophaga tridactyla) lives in savannas. ^[6] The two anteaters of the genus Tamandua, the southern (Tamandua tetradactyla) and the northern tamanduas (Tamandua mexicana), are much smaller than the giant anteater, and differ essentially from it in their habits, being mainly arboreal. They inhabit the dense primeval forests of South and Central America. The usual colour is yellowish-white, with a broad black lateral band, covering nearly the whole of the side of the body.

The silky anteater (Cyclopes didactylus) is a native of the hottest parts of South and Central America, and about the size of a cat, of a general yellowish color, and exclusively arboreal in its habits.

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Evolution

Anteaters are one of three surviving families of a once diverse group of mammals that occupied South America while it was geographically isolated from an invasion of animals from North America, the other two being the sloths and the armadillos.

At one time, anteaters were assumed to be related to aardvarks and pangolins because of their physical similarities to those animals, but these similarities have since been determined to be not a sign of a common ancestor, but of convergent evolution. All have evolved powerful digging forearms, long tongues, and toothless, tube-like snouts to subsist by raiding termite mounds. This similarity is the reason aardvarks are also commonly called "anteaters"; the pangolin has been called the "scaly anteater"; and the word "antbear" is a common term for both the aardvark and the giant anteater.

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Popular culture

• In recent years, the anteater has emerged in children's books, television shows, and other forms of entertainment. One such anteater is Francis the Anteater.
• An anteater is also the mascot of the University of California, Irvine, named Peter the Anteater.
• A talking giant anteater (sometimes shown with a giant, fanged maw) is also featured prominently in the television series Kingdom Hospital as the alter ego of a main character (Anubis).
• An anteater named Sniffles is one of the main characters of the internet series Happy Tree Friends.
• Heatmor, a Pokémon from Generation V of the video game series is based on an anteater. Its counterpart Pokémon is Durant.
• Salvador Dali used to own an anteater and walk it in the streets of Paris, France

Ant

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Etymology

The word "ant" is derived from ante, emete of Middle English which are derived from ǣmette of Old English, and is related to the dialectalDutch emt and the Old High German āmeiza, hence the modern German Ameise. All of these words come from West Germanic *ēmaitijǭ, and the original meaning of the word was "the biter" (from Proto-Germanic *ai-, "off, away" + *mait- "cut").^[13][14] The family name Formicidae is derived from the Latin formīca ("ant")^[15] from which the words in other Romance languages, such as the Portugueseformiga, Italian formica, Spanish hormiga, Romanian furnică, and French fourmi are derived. It has been hypothesised that a Proto-Indo-European word *morwi- was used, cf. Sanskrit vamrah, Latin formīca, Greek μύρμηξ mýrmēx, Old Church Slavonic mraviji, Old Irish moirb,Old Norse maurr, Dutch mier.

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Taxonomy and evolution

During the Cretaceous period, a few species of primitive ants ranged widely on the Laurasian supercontinent (the Northern Hemisphere). They were scarce in comparison to the populations of other insects, representing only about 1% of the entire insect population. Ants became dominant after adaptive radiation at the beginning of the Paleogene period. By the Oligocene and Miocene, ants had come to represent 20–40% of all insects found in major fossil deposits. Of the species that lived in the Eocene epoch, around one in 10 genera survive to the present. Genera surviving today comprise 56% of the genera in Baltic amber fossils (early Oligocene), and 92% of the genera in Dominican amber fossils (apparently early Miocene).^[20][25]The family Formicidae belongs to the order Hymenoptera, which also includes sawflies, bees, andwasps. Ants evolved from a lineage within the aculeate wasps, and a 2013 study suggests they are a sister group of the Apoidea.^[17] In 1966, E. O. Wilson and his colleagues identified the fossilremains of an ant (Sphecomyrma) that lived in the Cretaceous period. The specimen, trapped in amber dating back to around 92 million years ago, has features found in some wasps, but not found in modern ants.^[18] Sphecomyrma possibly was a ground forager, while Haidomyrmex andHaidomyrmodes, related genera in subfamily Sphecomyrminae, are reconstructed as active arboreal predators.^[19] After the rise of flowering plants about 100 million years ago they diversified and assumed ecological dominance around 60 million years ago.^{[20][21][22][23]} Some groups, such as the Leptanillinae and Martialinae, are suggested to have diversified from early primitive ants that were likely to have been predators underneath the surface of the soil.^[2][24]

Termites, although sometimes called 'white ants', are not ants. They belong to the sub-order Isoptera within order Blattodea. Termites are more closely related to cockroachesand mantids. Termites are eusocial, but differ greatly in the genetics of reproduction. The similarity of their social structure to that of ants is attributed to convergent evolution.^[26]Velvet ants look like large ants, but are wingless female wasps.

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Distribution and diversity

Ants are found on all continents except Antarctica, and only a few large islands, such as Greenland, Iceland, parts of Polynesia and the Hawaiian Islands lack native ant species.^[30][31] Ants occupy a wide range of ecological niches, and are able to exploit a wide range of food resources either as direct or indirect herbivores, predators, and scavengers. Most species are omnivorous generalists, but a few are specialist feeders. Their ecological dominance may be measured by their biomass and estimates in different environments suggest that they contribute 15–20% (on average and nearly 25% in the tropics) of the total terrestrial animal biomass, which exceeds that of the vertebrates.^[8]

Ants range in size from 0.75 to 52 millimetres (0.030–2.0 in),^[32][33] the largest species being the fossil Titanomyrma giganteum, the queen of which was 6 centimetres (2.4 in) long with a wingspan of 15 centimetres (5.9 in).^[34] Ants vary in colour; most ants are red or black, but a few species are green and some tropical species have a metallic lustre. More than 12,000 species are currently known (with upper estimates of the potential existence of about 22,000) (see the article List of ant genera), with the greatest diversity in the tropics. Taxonomic studies continue to resolve the classification and systematics of ants. Online databases of ant species, including AntBase and the Hymenoptera Name Server, help to keep track of the known and newly described species.^[35] The relative ease with which ants may be sampled and studied in ecosystems has made them useful as indicator species in biodiversity studies.

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Morphology

Ants are distinct in their morphology from other insects in having elbowed antennae, metapleural glands, and a strong constriction of their second abdominal segment into a node-like petiole. The head, mesosoma, and metasoma are the three distinct body segments. The petiole forms a narrow waist between their mesosoma (thorax plus the first abdominal segment, which is fused to it) and gaster (abdomen less the abdominal segments in the petiole). The petiole may be formed by one or two nodes (the second alone, or the second and third abdominal segments).^[38]

ther insects, ants have an exoskeleton, an external covering that provides a protective casing around the body and a point of attachment for muscles, in contrast to the internal skeletons of humans and other vertebrates. Insects do not have lungs; oxygen and other gases such as carbon dioxide pass through their exoskeleton via tiny valves called spiracles. Insects also lack closed blood vessels; instead, they have a long, thin, perforated tube along the top of the body (called the "dorsal aorta") that functions like a heart, and pumpshaemolymph toward the head, thus driving the circulation of the internal fluids. The nervous system consists of a ventral nerve cord that runs the length of the body, with several ganglia and branches along the way reaching into the extremities of the appendages.^[39]

An ant's head contains many sensory organs. Like most insects, ants have compound eyes made from numerous tiny lenses attached together. Ant eyes are good for acute movement detection, but do not offer a high resolution image. They also have three small ocelli (simple eyes) on the top of the head that detect light levels andpolarization.^[40] Compared to vertebrates, most ants have poor-to-mediocre eyesight and a few subterranean species are completely blind. Some ants such as Australia's bulldog ant, however, have excellent vision and are capable of discriminating the distance and size of objects moving nearly a metre away.^[41]§Head

Two antennae ("feelers") are attached to the head; these organs detect chemicals, air currents, and vibrations; they also are used to transmit and receive signals through touch. The head has two strong jaws, the mandibles, used to carry food, manipulate objects, construct nests, and for defence.^[39] In some species a small pocket (infrabuccal chamber) inside the mouth stores food, so it may be passed to other ants or their larvae.^[42]

§Legs

All six legs are attached to the mesosoma ("thorax") and terminate in a hooked claw.

§Wings

Only reproductive ants, queens and males, have wings. Queens shed the wings after the nuptial flight, leaving visible stubs, a distinguishing feature of queens. Wingless queens (ergatoids) and males occur in a few species, however.

§Metasoma

The metasoma (the "abdomen") of the ant houses important internal organs, including those of the reproductive, respiratory (tracheae), and excretory systems. Workers of many species have their egg-laying structures modified into stings that are used for subduing prey and defending their nests.

§Polymorphism

In the colonies of a few ant species, there are physical castes—workers in distinct size-classes, called minor, median, and major workers. Often, the larger ants have disproportionately larger heads, and correspondingly stronger mandibles. Such individuals are sometimes called "soldier" ants because their stronger mandibles make them more effective in fighting, although they still are workers and their "duties" typically do not vary greatly from the minor or median workers. In a few species, the median workers are absent, creating a sharp divide between the minors and majors. Weaver ants, for example, have a distinct bimodal size distribution.Some other species show continuous variation in the size of workers. The smallest and largest workers in Pheidologeton diversus show nearly a 500-fold difference in their dry-weights. Workers cannot mate; however, because of the haplodiploid sex-determination system in ants, workers of a number of species can lay unfertilised eggs that become fully fertile, haploid males. The role of workers may change with their age and in some species, such as honeypot ants, young workers are fed until their gasters are distended, and act as living food storage vessels. These food storage workers are called repletes.For instance, these replete workers develop in the North American honeypot ant Myrmecocystus mexicanus. Rissing found that usually the largest workers in the colony develop into repletes, and if repletes are removed from the colony other workers become repletes, demonstrating the flexibility of this particular polymorphism. This polymorphism in morphology and behaviour of workers initially was thought to be determined by environmental factors such as nutrition and hormones that led to different developmental paths; however, genetic differences between worker castes have been noted in Acromyrmex sp. These polymorphisms are caused by relatively small genetic changes; differences in a single gene of Solenopsis invicta can decide whether the colony will have single or multiple queens. The Australian jack jumper ant (Myrmecia pilosula) has only a single pair of chromosomes (with the males having just one chromosome as they are haploid), the lowest number known for any animal, making it an interesting subject for studies in the genetics and developmental biology of social insects.

Development and reproduction

The larvae grow through a series of four or five moults and enter the pupal stage. The pupa has the appendages free and not fused to the body as in a butterfly pupa. The differentiation into queens and workers (which are both female), and different castes of workers (when they exist), is influenced in some species by the nutrition the larvae obtain. Genetic influences and the control of gene expression by the developmental environment are complex and the determination of caste continues to be a subject of research. Larvae and pupae need to be kept at fairly constant temperatures to ensure proper development, and so often, are moved around among the various brood chambers within the colony.The life of an ant starts from an egg. If the egg is fertilised, the progeny will be female (diploid); if not, it will be male (haploid). Ants develop by complete metamorphosis with the larva stages passing through a pupal stage before emerging as an adult. The larva is largely immobile and is fed and cared for by workers. Food is given to the larvae by trophallaxis, a process in which an ant regurgitates liquid food held in its crop. This is also how adults share food, stored in the "social stomach". Larvae, especially in the later stages, may also be provided solid food such as trophic eggs, pieces of prey, and seeds brought by workers.

A new worker spends the first few days of its adult life caring for the queen and young. She then graduates to digging and other nest work, and later to defending the nest and foraging. These changes are sometimes fairly sudden, and define what are called temporal castes. An explanation for the sequence is suggested by the high casualties involved in foraging, making it an acceptable risk only for ants who are older and are likely to die soon of natural causes.

Most ants are univoltine, producing a new generation each year. During the species-specific breeding period, new reproductives, females and winged males leave the colony in what is called a nuptial flight. Typically, the males take flight before the females. Males then use visual cues to find a common mating ground, for example, a landmark such as a pine tree to which other males in the area converge. Males secrete a mating pheromone that females follow. Females of some species mate with just one male, but in others they may mate with as many as ten or more different males.Most ant species have a system in which only the queen and breeding females have the ability to mate. Contrary to popular belief, some ant nests have multiple queens, while others may exist without queens. Workers with the ability to reproduce are called "gamergates" and colonies that lack queens are then called gamergate colonies; colonies with queens are said to be queen-right.^[58] The winged male ants, called drones, emerge from pupae along with the breeding females (although some species, such as army ants, have wingless queens), and do nothing in life except eat and mate.

Mated females then seek a suitable place to begin a colony. There, they break off their wings and begin to lay and care for eggs. The females store the sperm they obtain during their nuptial flight to selectively fertilise future eggs. The first workers to hatch are weak and smaller than later workers, but they begin to serve the colony immediately. They enlarge the nest, forage for food, and care for the other eggs. This is how new colonies start in most ant species. Species that have multiple queens may have a queen leaving the nest along with some workers to found a colony at a new site,^[60] a process akin to swarming in honeybees.

Ant colonies can be long-lived. The queens can live for up to 30 years, and workers live from 1 to 3 years. Males, however, are more transitory, being quite short-lived and surviving for only a few weeks.Ant queens are estimated to live 100 times longer than solitary insects of a similar size.^[63]A wide range of reproductive strategies have been noted in ant species. Females of many species are known to be capable of reproducing asexually through thelytokous parthenogenesis.

Ants are active all year long in the tropics, but, in cooler regions, they survive the winter in a state of dormancy or inactivity. The forms of inactivity are varied and some temperate species have larvae going into the inactive state, (diapause), while in others, the adults alone pass the winter in a state of reduced activity.

§

Behaviour and ecology

Communication

Ants use pheromones for more than just making trails. A crushed ant emits an alarm pheromone that sends nearby ants into an attack frenzy and attracts more ants from farther away. Several ant species even use "propaganda pheromones" to confuse enemy ants and make them fight among themselves.^[] Pheromones are produced by a wide range of structures including Dufour's glands, poison glands and glands on the hindgut, pygidium, rectum, sternum, and hind tibia.^[63] Pheromones also are exchanged, mixed with food, and passed by trophallaxis, transferring information within the colony.^[] This allows other ants to detect what task group (e.g., foraging or nest maintenance) other colony members belong to.^[] In ant species with queen castes, when the dominant queen stops producing a specific pheromone, workers begin to raise new queens in the colony.^[]Ants communicate with each other using pheromones, sounds, and touch.^[] The use of pheromones as chemical signals is more developed in ants, such as the red harvester ant, than in other hymenopteran groups. Like other insects, ants perceive smells with their long, thin, and mobile antennae. The paired antennae provide information about the direction and intensity of scents. Since most ants live on the ground, they use the soil surface to leave pheromone trails that may be followed by other ants. In species that forage in groups, a forager that finds food marks a trail on the way back to the colony; this trail is followed by other ants, these ants then reinforce the trail when they head back with food to the colony. When the food source is exhausted, no new trails are marked by returning ants and the scent slowly dissipates. This behaviour helps ants deal with changes in their environment. For instance, when an established path to a food source is blocked by an obstacle, the foragers leave the path to explore new routes. If an ant is successful, it leaves a new trail marking the shortest route on its return. Successful trails are followed by more ants, reinforcing better routes and gradually identifying the best path.^[66]

Some ants produce sounds by stridulation, using the gaster segments and their mandibles. Sounds may be used to communicate with colony members or with other species.

§Defence

Ants attack and defend themselves by biting and, in many species, by stinging, often injecting or spraying chemicals, such as formic acidin the case of formicine ants, alkaloids and piperidines in fire ants, and a variety of protein components in other ants. Bullet ants(Paraponera), located in Central and South America, are considered to have the most painful sting of any insect, although it is usually not fatal to humans. This sting is given the highest rating on the Schmidt Sting Pain Index.See also Insect defences

The sting of jack jumper ants can be fatal, and an antivenom has been developed for it.

Fire ants, Solenopsis spp., are unique in having a poison sac containing piperidine alkaloids. Their stings are painful and can be dangerous to hypersensitive people.

A Malaysian species of ant in the Camponotus cylindricus group has enlarged mandibular glands that extend into their gaster. When disturbed, workers rupture the membrane of the gaster, causing a burst of secretions containing acetophenones and other chemicals that immobilise small insect attackers. The worker subsequently dies.Trap-jaw ants of the genus Odontomachus are equipped with mandibles called trap-jaws, which snap shut faster than any other predatory appendages within the animal kingdom.^[] One study of Odontomachus bauri recorded peak speeds of between 126 and 230 km/h (78 – 143 mph), with the jaws closing within 130 microseconds on average. The ants were also observed to use their jaws as a catapult to eject intruders or fling themselves backward to escape a threat.^[77] Before striking, the ant opens its mandibles extremely widely and locks them in this position by an internal mechanism. Energy is stored in a thick band of muscleand explosively released when triggered by the stimulation of sensory organs resembling hairs on the inside of the mandibles. The mandibles also permit slow and fine movements for other tasks. Trap-jaws also are seen in the following genera: Anochetus,Orectognathus, and Strumigenys, plus some members of the Dacetini tribe,^[78] which are viewed as examples of convergent evolution.

Suicidal defences by workers are also noted in a Brazilian ant, Forelius pusillus, where a small group of ants leaves the security of the nest after sealing the entrance from the outside each evening.^[80]

Nests may be protected from physical threats such as flooding and overheating by elaborate nest architecture.^[84][85] Workers ofCataulacus muticus, an arboreal species that lives in plant hollows, respond to flooding by drinking water inside the nest, and excreting it outside.^[86] Camponotus anderseni, which nests in the cavities of wood in mangrove habitats, deals with submergence under water by switching to anaerobic respiration.In addition to defence against predators, ants need to protect their colonies from pathogens. Some worker ants maintain the hygiene of the colony and their activities include undertaking or necrophory, the disposal of dead nest-mates.^[81] Oleic acid has been identified as the compound released from dead ants that triggers necrophoric behaviour in Atta mexicana while workers of Linepithema humile react to the absence of characteristic chemicals (dolichodial and iridomyrmecin) present on the cuticle of their living nestmates to trigger similar behaviour.

§Learning

Many animals can learn behaviours by imitation, but ants may be the only group apart from mammals where interactive teaching has been observed. A knowledgeable forager ofTemnothorax albipennis will lead a naive nest-mate to newly discovered food by the process of tandem running. The follower obtains knowledge through its leading tutor. The leader is acutely sensitive to the progress of the follower and slows down when the follower lags and speeds up when the follower gets too close.

Controlled experiments with colonies of Cerapachys biroi suggest that an individual may choose nest roles based on her previous experience. An entire generation of identical workers was divided into two groups whose outcome in food foraging was controlled. One group was continually rewarded with prey, while it was made certain that the other failed. As a result, members of the successful group intensified their foraging attempts while the unsuccessful group ventured out fewer and fewer times. A month later, the successful foragers continued in their role while the others had moved to specialise in brood care.

§Nest construction

Complex nests are built by many ant species, but other species are nomadic and do not build permanent structures. Ants may form subterranean nests or build them on trees. These nests may be found in the ground, under stones or logs, inside logs, hollow stems, or even acorns. The materials used for construction include soil and plant matter,^[60] and ants carefully select their nest sites; Temnothorax albipennis will avoid sites with dead ants, as these may indicate the presence of pests or disease. They are quick to abandon established nests at the first sign of threats.

The army ants of South America, such as the Eciton burchellii species, and the driver ants of Africa do not build permanent nests, but instead, alternate between nomadism and stages where the workers form a temporary nest (bivouac) from their own bodies, by holding each other together.

Weaver ant (Oecophylla spp.) workers build nests in trees by attaching leaves together, first pulling them together with bridges of workers and then inducing their larvae to produce silk as they are moved along the leaf edges. Similar forms of nest construction are seen in some species of Polyrhachis.

Formica polyctena, among other ant species, constructs nests that maintain a relatively constant interior temperature that aids in the development of larvae. The ants maintain the nest temperature by choosing the location, nest materials, controlling ventilation and maintaining the heat from solar radiation, worker activity and metabolism, and in some moist nests, microbial activity in the nest materials.^[93]

Some ant species, such as those that use natural cavities, can be opportunistic and make use of the controlled micro-climate provided inside human dwellings and other artificial structures to house their colonies and nest structures.

§Cultivation of food

Most ants are generalist predators, scavengers, and indirect herbivores, but a few have evolved specialised ways of obtaining nutrition. It is believed that many ant species that engage in indirect herbivory rely on specialized symbiosis with their gut microbes  to upgrade the nutritional value of the food they collect ^[97] and allow them to survive in nitrogen poor regions, such as rainforrest canopies.^[]Leafcutter ants (Atta and Acromyrmex) feed exclusively on a fungus that grows only within their colonies. They continually collect leaves which are taken to the colony, cut into tiny pieces and placed in fungal gardens. Workers specialise in related tasks according to their sizes. The largest ants cut stalks, smaller workers chew the leaves and the smallest tend the fungus. Leafcutter ants are sensitive enough to recognise the reaction of the fungus to different plant material, apparently detecting chemical signals from the fungus. If a particular type of leaf is found to be toxic to the fungus, the colony will no longer collect it. The ants feed on structures produced by the fungi calledgongylidia. Symbiotic bacteria on the exterior surface of the ants produce antibiotics that kill bacteria introduced into the nest that may harm the fungi.

Navigation

Foraging ants travel distances of up to 200 metres (700 ft) from their nest  and scent trails allow them to find their way back even in the dark. In hot and arid regions, day-foraging ants face death by desiccation, so the ability to find the shortest route back to the nest reduces that risk. Diurnal desert ants of the genus Cataglyphis such as the Sahara desert ant navigate by keeping track of direction as well as distance travelled. Distances travelled are measured using an internal pedometer that keeps count of the steps taken ^] and also by evaluating the movement of objects in their visual field (optical flow).^[] Directions are measured using the position of the sun.They integrate this information to find the shortest route back to their nest.^[] Like all ants, they can also make use of visual landmarks when available ^[] as well as olfactory and tactile cues to navigate.Some species of ant are able to use the Earth's magnetic fieldfor navigation.^[108] The compound eyes of ants have specialised cells that detect polarised light from the Sun, which is used to determine direction. These polarization detectors are sensitive in the ultraviolet region of the light spectrum. In some army ant species, a group of foragers who become separated from the main column sometimes may turn back on themselves and form a circular ant mill. The workers may then run around continuously until they die of exhaustion.

Locomotion

The female worker ants do not have wings and reproductive females lose their wings after their mating flights in order to begin their colonies. Therefore, unlike their wasp ancestors, most ants travel by walking. Some species are capable of leaping. For example, Jerdon's jumping ant (Harpegnathos saltator) is able to jump by synchronising the action of its mid and hind pairs of legs.^[113] There are several species of gliding ant including Cephalotes atratus; this may be a common trait among most arboreal ants. Ants with this ability are able to control the direction of their descent while falling.^[114]

Other species of ants can form chains to bridge gaps over water, underground, or through spaces in vegetation. Some species also form floating rafts that help them survive floods. These rafts may also have a role in allowing ants to colonise islands.^[115] Polyrhachis sokolova, a species of ant found in Australian mangrove swamps, can swim and live in underwater nests. Since they lack gills, they go to trapped pockets of air in the submerged nests to breathe.

§Cooperation and competition

Some species (such as Tetramorium caespitum) attack and take over neighbouring ant colonies. Others are less expansionist, but just as aggressive; they invade colonies to steal eggs or larvae, which they either eat or raise as workers or slaves. Extreme specialists among these slave-raiding ants, such as the Amazon ants, are incapable of feeding themselves and need captured workers to survive.^[118]Captured workers of the enslaved species Temnothorax have evolved a counter strategy, destroying just the female pupae of the slave-making Protomognathus americanus, but sparing the males (who don't take part in slave-raiding as adults).Not all ants have the same kind of societies. The Australian bulldog ants are among the biggest and most basal of ants. Like virtually all ants, they are eusocial, but their social behaviour is poorly developed compared to other species. Each individual hunts alone, using her large eyes instead of chemical senses to find prey.

Parasitic ant species enter the colonies of host ants and establish themselves as social parasites; species such as Strumigenys xenos are entirely parasitic and do not have workers, but instead, rely on the food gathered by their Strumigenys perplexa hosts.This form of parasitism is seen across many ant genera, but the parasitic ant is usually a species that is closely related to its host. A variety of methods are employed to enter the nest of the host ant. A parasitic queen may enter the host nest before the first brood has hatched, establishing herself prior to development of a colony scent. Other species use pheromones to confuse the host ants or to trick them into carrying the parasitic queen into the nest. Some simply fight their way into the nest.Ants identify kin and nestmates through their scent, which comes from hydrocarbon-laced secretions that coat their exoskeletons. If an ant is separated from its original colony, it will eventually lose the colony scent. Any ant that enters a colony without a matching scent will be attacked.^[120] Also, the reason why two separate colonies of ants will attack each other even if they are of the same species is because the genes responsible for pheromone production are different between them. TheArgentine ant, however, does not have this characteristic, due to lack of genetic diversity, and has become a global pest because of it.

A conflict between the sexes of a species is seen in some species of ants with these reproducers apparently competing to produce offspring that are as closely related to them as possible. The most extreme form involves the production of clonal offspring. An extreme of sexual conflict is seen in Wasmannia auropunctata, where the queens produce diploid daughters by thelytokous parthenogenesis and males produce clones by a process whereby a diploid egg loses its maternal contribution to produce haploid males who are clones of the father.