Ants are eusocial insects of the family Formicidae and, along
with the related families of wasps and bees, belong to the order
Hymenoptera. They are a diverse group of more than 12,000
species, with a higher diversity in the tropics. They are known
for their highly organized colonies and nests, which sometimes
consist of millions of individuals. Individuals are divided into
sub-fertile, and more commonly sterile, females ("workers"),
fertile males ("drones"), and fertile females ("queens").
Colonies can occupy and use a wide area of land to support
themselves. Ant colonies are sometimes described as
superorganisms because the colony appears to operate as a single
Ants have colonized almost every landmass on Earth. The only places lacking indigenous ant species are Antarctica, Greenland, Iceland, and the Hawaiian Islands. When all their individual contributions are added up, they may constitute up to 15 to 25% of the total terrestrial animal biomass.
Termites, sometimes called white ants, are not closely related to ants, although they have similar social structures. Velvet ants, although resembling large ants, are wingless female wasps.
The Formicidae family belongs to the order Hymenoptera, which also includes sawflies, bees and wasps. Ants are a lineage derived from within the vespoid wasps. Phylogenetic analysis indicates that ants evolved from vespoids in the mid-Cretaceous period about 120 to 170 million years ago. After the rise of angiosperms about 100 million years ago, they increased in diversity and assumed ecological dominance about 60 million years ago. Several fossils from the Cretaceous are intermediate in form between wasps and ants, establishing further evidence for wasp ancestry. Like other Hymenoptera, the genetic system found in ants is haplodiploidy.
In 1966 E. O. Wilson, et al. obtained the first amber fossil
remains of an ant (Sphecomyrma freyi) from the Cretaceous era.
The specimen was trapped in amber from New Jersey that was more
than 80 million years old. This species provides the clearest
evidence of a link between modern ants and non-social wasps.
Cretaceous ants shared both wasp-like and modern ant-like
During the Cretaceous era, representatives of only a few species of primitive ants ranged widely on what was the super-continent Laurasia (the northern hemisphere). They were scarce in comparison to other insects (about only 1%). The ants became dominant in an adaptive radiation at the beginning of the Tertiary Period. Of the species extant in the Cretaceous and Eocene eras, only 1 of about 10 genera is now extinct. 56% of the genera represented on the Baltic amber fossils (early Oligocene), and 96% of the genera represented in the Dominican amber fossils (apparently early Miocene) still survive today.
Ants are distinguished from other insects by the following traits: elbowed antennae; the presence of a metapleural gland; a strongly constricted second abdominal segment forming a distinct node-like petiole, 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 can be formed by one or two nodes (only the second, or the second and third abdominal segments can form it). Ants have a wingless worker caste.
Ant bodies, like those of other insects, have an exoskeleton, meaning their bodies are externally covered in a protective casing, as opposed to the internal skeletal framework of humans and other vertebrates. Ants do not have lungs. Oxygen passes through tiny valves, the spiracles, in their exoskeleton — the same holes through which carbon dioxide leaves their body. Nor do they have a heart[vague]; a colorless blood, the hemolymph, runs from their head to rear and back again along a long tube. Their nervous system is much like a human spinal cord in that it is a continuous cord, the ventral nerve cord, from head to rear with branches into each extremity.
The three main divisions of the ant body are the head, mesosoma and metasoma or gaster.
The head of an ant has many important parts. Ant eyes include the compound eyes, similar to fly eyes: numerous tiny lenses attached together which enables them to see movement very well. They also have three small ocelli on the top of the head, which detect light and dark. Most ants have poor to mediocre eyesight; some are blind altogether. A few have exceptional vision though, such as Australia's bulldog ant. Also attached to the head of an ant are two antennae ("feelers"). The antennae are special organs that help ants detect chemicals, including those used in communication, as well as a sense of touch. Ants release pheromones to communicate with each other and the antennae pick up these chemical signals. The head also has two strong jaws, the mandibles, which are used to carry food, manipulate objects, construct nests, and for defense. In some species there is also a small pocket inside the mouth to hold food for passing to others.
The thorax of the ant is where all six legs are attached. At the end of each leg is a hooked claw that helps ants climb and hang onto things. Most queens and male ants have wings, which they drop after the nuptial flight. The wing scars are then visible, a distinguishing feature of queens. Wingless queens (ergatoids) and males can also occur.
The metasoma (the "abdomen") of the ant houses many of the important internal organs, including the reproductive organs. Many species of ants have stingers used for subduing prey and defending their nests.
The life of an ant starts with an egg. If the egg is fertilized, the ant will be female (diploid); if not, it will be male (haploid). Ants are holometabolous, and develop by complete metamorphosis, passing through larval and pupal stages (with the pupae being exarate) before they become adults. The larval stage is particularly helpless — for instance it lacks legs entirely – and cannot care for itself. The difference between queens and workers (which are both female), and between different castes of workers when they exist, is determined by the feeding in the larval stage. Food is given to the larvae by a process called trophallaxis in which an ant regurgitates food previously held in its crop for communal storage. This is also how adults distribute food amongst themselves. Larvae and pupae need to be kept at fairly constant temperatures to ensure proper development, and so are often moved around the various brood chambers within the colony.
A new worker spends the first few days of its adult life caring for the queen and young. After that it graduates to digging and other nest work, and then to foraging and defense of the nest. These changes are fairly abrupt and define what are called temporal castes. One theory of why this occurs is because foraging has a high death rate, so ants only participate in it when they are older and closer to death anyway. In a few ants there are also physical castes — workers come in a spectrum of sizes, called minor, median, and major workers, the latter beginning foraging sooner. Often the larger ants will 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 other creatures, although they are still in fact worker ants and their "duties" typically do not vary greatly from the minor or median workers. In a few species the median workers have disappeared, creating a sharp divide and clear physical difference between the minors and majors.
Most of the common ant species breed in the same way. Only the queen and breeding females have the ability to mate. Contrary to popular belief, some ant nests have multiple queens. The male ants, called drones, along with the breeding females emerge from pupation with wings (although some species, like army ants, do not produce winged queens), and do nothing throughout their life except eat and mate. At this time, all breeding ants, excluding the queen, are carried outside where other colonies of similar species are doing the same. Then, all the winged breeding ants take flight. Mating occurs in flight and the males die shortly afterward. The females that survive land and seek a suitable place to begin a colony. There, they break off their own wings and begin to lay eggs, which they care for. Sperm obtained during their nuptial flight is stored and used to fertilize all future eggs produced. 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 most new colonies start. A few species that have multiple queens can start a new colony as a queen from the old nest takes a number of workers to a new site and founds a colony there.
Ant colonies can be long-lived. The queens themselves can live for up to 30 years, while workers live from 1 to 3 years. Males, however, are short lived and live for only a few weeks.
Ants survive the winter by going into a state of dormancy or inactivity. The forms of inactivity are varied and some temperate species have larvae that go into diapause while in others the adults alone pass the winter in a state of reduced activity. This does not happen in the tropics.
Ants show a wide range of morphological differences between the castes. While in some species, these differences are small, they are large in others. In some ant species there can be several size variants within the worker castes. The gonads in the workers are not functional, and sometimes they are even strongly reduced.
Some ants, called honeypot ants, have special workers called repletes who simply store food for the rest of the colony, generally becoming immobile with greatly enlarged abdomens. In hot, dry places, even deserts, in Africa, North America, and Australia where they live, they are considered by some people to be a great delicacy.
Ant communication is accomplished primarily through chemicals called pheromones. Because most ants spend their time in direct contact with the ground, these chemical messages are more developed than in other hymenopterans. So for instance, when a forager finds food, she will leave a pheromone trail along the ground on her way home. In a short time other ants will follow this pheromone trail. Home is often located through the use of remembered landmarks and the position of the sun as detected with compound eyes and also by means of special sky polarization-detecting fibers within the eyes. Returning home, they reinforce the same trail which in turn attracts more ants until the food is exhausted, after which the trail scent slowly dissipates. This behavior helps ants adapt to changes in their environment. When an established path to a food source is blocked by a new obstacle, the foragers leave the path to explore new routes. If successful, the returning ant leaves a new trail marking the shortest route. Since each ant prefers to follow a path richer in pheromone rather than poorer, the resulting route is also the shortest available.
Ants make use of pheromones for other purposes as well. A crushed ant, for example, will emit an alarm pheromone which in high concentration sends nearby ants into an attack frenzy; and in lower concentration, merely attracts them. To confuse their enemies several ant species even employ "propaganda pheromones", which cause their enemies to fight among themselves.
Like other insects, ants smell with their antennae, which are long and thin. These are fairly mobile, having a distinct elbow joint after an elongated first segment; and since they come in pairs—rather like binocular vision or stereophonic sound equipment—they provide information about direction as well as intensity. Pheromones are also exchanged as compounds mixed with food and passed in trophallaxis, giving the ants information about one another's health and nutrition. Ants can also detect what task group (e.g. foraging or nest maintenance) to which other ants belong. Of special note, the queen produces a certain pheromone without which the workers would begin raising new queens.
Some ants also produce sounds by stridulating using the gaster segments and also using their mandibles. They may serve to communicate among colony members as well as in interactions with other species.
Weaver ants collaborating to dismember a red ant (the two at the extremities are pulling the red ant, while the middle one cuts the red ant until she snaps)Ants attack others and defend themselves by biting and in many species, stinging, often injecting chemicals like formic acid. Bullet ants (the genus Paraponera), located in Central and South America, are considered to have the most painful sting among insects, although these are usually non-fatal. They are given the highest rating on the Schmidt Sting Pain Index. Jack jumper ants, Myrmecia pilosula, located in Australia have stings that cause fatality to a small number of people in the population, and cause hospitalizations each year. A vaccine based on use of the venom extract to develop immunity has been developed.
Fire ants, Solenopsis spp., are unique in having a poison sac containing piperidine alkaloids.
Some ants of the genus Odontomachus are equipped with mandibles called trap-jaws. This snap-jaw mechanism, or catapult mechanism, is possible because energy is stored in the large closing muscles. The blow is incredibly fast, about 0.5 ms in the genus Mystrium. Before the strike, the mandibles open wide and are locked in the open position by the labrum, which functions as a latch. The attack is triggered by stimulation of sensory hairs at the side of the mandibles. The mandibles are also able to function as a tool for more finely adjusted tasks. Two similar groups are Odontomachus and Dacetini - examples of convergent evolution.
Apart from defense against larger threats, ants also need to defend their colonies against disease organisms. Some ant workers' role is to maintain the hygiene of the colony and their activities include undertaking or necrophory, the transport of dead nest-mates. Oleic acid is identified as one compound released by dead ants that triggers undertaking behavior in Atta mexicana.
The nests are also protected from physical threats such as flooding by elaborate structures at the entrance or special chambers for escaping from flooding. Some arboreal species that live in plant hollows (Phytotelmata) also have behavioral responses to flooding, where the workers drink the water and excrete it outside the nest.
While many types of animals can learn behaviors by imitating other animals, ants may be the only group of animals besides primates and some other mammals in which interactive teaching behavior has been observed. Knowledgeable forager ants of the species Temnothorax albipennis directly lead naïve nest-mates to newly discovered food sources by the excruciatingly slow (and time-costly) process of tandem running. The follower thereby obtains knowledge that it would not have, had it not been tutored, and this is at the expense of its nest-mate teacher. Both leader and follower are acutely sensitive to the progress of their partner. For example, the leader slows down when the follower lags too far behind, and speeds up when the follower gets too close, while the follower does the opposite.
While some ants form complex nests and galleries, other species are nomadic and do not build permanent structures. Various species may form subterranean nests or build them on trees. Nests can be found in the ground with craters or mounds around the entrance, under stones or logs, in logs, hollow stems, even acorns. The materials used for construction include soil and plant matter, and they are highly selective of the nest site; Temnothorax albipennis will avoid sites with dead ants as these may be indicators of pests or disease. They are also quick to abandon established nest sites at the first sign of these threats.
Some of the more advanced ants are the army ants and driver ants, from South America and Africa respectively. Unlike most species which have permanent nests, army and driver ants do not form permanent nests, but instead alternate between nomadic stages and stages where the workers form a temporary nest (bivouac) out of their own bodies. Colonies reproduce either through nuptial flights as described above, or by fission, where a group of workers simply dig a new hole and raise new queens. Colony members are distinguished by smell, and other intruders are usually attacked.
Weaver ants (Oecophylla) build nests in trees by attaching leaves together, first pulling them together with bridges of workers and then sewing them together by pressing silk-producing larvae against them in alternation.
Leafcutter ants (Atta and Acromyrmex) feed exclusively on a special fungus that lives only within their colonies. They continually collect leaves which they cut into tiny pieces for the fungus to grow on. There are different sized castes specially suited to finer and finer tasks of cutting and chewing the leaves and tending to the garden. Leaf cutter ants are sensitive enough to adapt to the fungi's reaction to different plant material, apparently detecting chemical signals from the fungus. If a particular type of leaf is toxic to the fungus the colony will no longer collect it. The ants grow the fungus because it produces special structures called gongylidia which are fed on by the ants. They create antibiotics on their exterior surfaces with the aid of symbiotic bacteria, and subsist entirely on this farming of the fungus.
Desert ants Cataglyphis fortis make use of visual landmarks in combination with other cues to navigate.
In the absence of visual landmarks, Sahara desert ants have been shown to navigate by keeping track of direction as well as distance traveled, like an internal pedometer that keeps tracks of how many steps they take, and use this information to find the shortest routes back to their nests.
Worker ants generally do not grow wings and reproductive females remove theirs after their mating flights in order to begin their colonies. Therefore, unlike their wasp ancestors, most ants travel by walking.
The more cooperative species of ants sometimes form chains to bridge gaps, whether that be over water, underground, or through spaces in arboreal paths. Some species also form floating rafts that help them survive floods. They may also have a role in colonization of islands.
Some ants are even capable of leaping. A particularly notable species is Jerdon's jumping ant, Harpegnathos saltator. This is achieved by synchronized action of the mid and hind pair of legs.
Polyrhachis sokolova, a species of ant found in Australian mangrove swamps, can swim and lives in nests that are submerged underwater. They make use of trapped pockets of air in the submerged nests.
There are several species of gliding ant including Cephalotes atratus. In fact this may be a common trait among most arboreal ants. Ants with this ability are able to direct the direction of their descent while falling.
Not all ants have the same kind of societies. The Australian bulldog ants are among the biggest and most primitive of ants. The individual hunts alone, using its large eyes instead of its chemical senses to find prey. Like all ants they are social, but their social behavior is poorly developed compared to more advanced species. An Australian bulldog ant, Myrmecia pilosula, has only a single pair of chromosomes and males have just one chromosome as they are haploid.
Some species of ants are known for attacking and taking over the colonies of other ant species. Others are less expansionist but nonetheless just as aggressive; they attack colonies to steal eggs or larvae, which they either eat or raise as workers/slaves. Some ants, such as the Amazon ants, are incapable of feeding themselves, and must rely on captured worker ants to care for them. In some cases ant colonies may have other species of ants or termites within the same nest.
The pavement ant is famous for its urge to increase its territory. In early spring, colonies attempt to conquer new areas and often attack the nearest enemy colony. These result in huge sidewalk battles, sometimes leaving thousands of ants dead. Because of their aggressive nature, they often invade and colonize seemingly impenetrable areas.
Ants identify kin and nestmates through their scents, a hydrocarbon-laced secretion that coats their exoskeletons. If an ant is separated from its original colony, it will eventually lose the colony scent. Any ant that enters a colony with a different scent than that of the colony will be attacked. (See also Kin selection)
There is a great diversity among ants and their behaviors. They
range in size from 2 to about 25 mm (about 0.08 to 1 inch).
Their color may vary; most are red or black, but other colors
can also be seen, including some tropical groups with a metallic
luster. (See also ant genera). Numerous species of ant continue
to be added in present times and taxonomic studies continue to
resolve the classification and systematic of ants. Online
databases of ant species include AntBase and the Hymenoptera
Ants have been used as indicator species in biodiversity studies.
Ants associate with a wide range of species in many ways. They form mutualisms with other insects, plants, and fungi. They parasitize each other. They are preyed upon by many animals and even certain fungi. Because their nests are such hospitable places, many species of arthropods sneak in and integrate themselves in various ways to the ant's daily lives.
Aphids secrete a sweet liquid called honeydew which they exude in the process of feeding from plants. The sugars can provide a high-energy food source, which many ant species collect. In some cases the aphids secrete the honeydew specially in response to the ants tapping them with their antennas. The ants in turn keep predators away and will move the aphids around to better feeding locations. Upon migrating to a new area, many colonies will take new aphids with them, to ensure that they have a supply of honeydew in the new area. Ants also tend mealybugs to harvest their honeydew. Mealybugs can become a serious pest of pineapple if ants are present to protect mealybugs from natural enemies.
Myrmecophilous (ant-loving) caterpillars of the family Lycaenidae (e.g., blues, coppers, or hairstreaks) are herded by the ants, led to feeding areas in the daytime, and brought inside the ants' nest at night. The caterpillars have a gland which secretes honeydew when the ants massage them. Some caterpillars are known to produce vibrations and sounds that are sensed by the ants. Some caterpillars have evolved from being ant-loving to ant-eating and these myrmecophagous caterpillars secrete a pheromone which makes the ants think that the caterpillar's larva is one of their own. The larva will then be taken into the ants' nest where it can feed on the ant larvae.
Fungus-growing ants that make up the tribe attini, including leafcutter ants, actively cultivate certain species of fungus in the Leucoagaricus or Leucocoprinus genera of the Agaricaceae family. In this ant-fungus mutualism, both species depend on each other for survival. The ant Allomerus decemarticulatus has evolved a tripartite association with their host plant Hirtella physophora (Chrysobalanaceae), and a sticky fungus which is used to trap their insect prey.
Lemon ants make devil's gardens by selectively killing surrounding plants and leaving a pure patch of lemon ant trees Duroia hirsuta. Many trees have extrafloral nectaries that provide food for ants and the ants in turn protect the plant from herbivorous insects. Some species like the bullhorn acacia, Acacia cornigera, in Central America have hollow thorns that serve to house colonies of stinging ants, Pseudomyrmex ferruginea, that defend the tree against insects, browsing mammals, and epiphytic vines. In return, the ants obtain food from protein-lipid Beltian bodies. Another example of this type of ectosymbiosis comes from the Macaranga tree which have stems adapted to house colonies of Crematogaster ants. Many tropical tree species have seeds that are dispersed by ants.
Flies in the Old World genus Bengalia (Calliphoridae) are kleptoparasites and predators on ants and often snatch prey or brood from the adult ants. Wingless and legless females of the Malaysian phorid fly Vestigipoda myrmolarvoidea live in the nests of ants of the genus Aenictus and are cared for by the ants.
Many species of birds show a peculiar behavior called anting that is as yet not fully understood. Here birds may rest on ant nests or pick and drop ants onto their wings and feathers, presumably to rid themselves of ectoparasites.
A fungus, Cordyceps, infects ants, causing them to climb up plants and sink their mandibles into the plant tissue. The fungus kills and engulfs the ant and produces its fruiting body. It appears that the fungus alters the behavior of the ant and uses the ant to help disperse its spores.
Some South American frogs in the genus Dendrobates feed primarily on ants and the toxins on their skin may be derived from the ants.
Brown bears (Ursus arctos) have been found to feed on ants, with as much as 12%, 16%, and 4% of their fecal volume in spring, summer, and autumn, respectively being made up of ants.
Many species of mammals such as anteaters, pangolins and several marsupial species in Australia have special adaptations for living on a primary diet of ants. These adaptations include long sticky tongues to pick the ants and strong claws to break into the ant nests. Some South American birds such as the antpittas are also ant predators.
This Ant Page is Copyright The Animal Web Guide © 2004 - 2009 Chuck Ayoub