Ant

This article is about the family of insects. For other uses, see Ant (disambiguation).

Ants are eusocial insects in the family Formicidae. They are related to wasps and bees, and all three belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors long ago, during the Cretaceous period. Scientists have described more than 13,800 species, and there may be about 22,000 in total. You can recognise ants by their bent antennae and their narrow waists, which have a small, knob-like shape.

Ants live in groups called colonies. Some colonies are small, with a few dozen ants, often living in natural cavities. Others are very well organised and can cover large areas, with nests that hold millions of ants. In some cases, super colonies reach hundreds of millions of ants. Most colonies have several groups of wingless females that cannot have young: workers (ergates) and soldiers (dinergates). Nearly all colonies also have some fertile males called "drones" and one or more fertile females called "queens" (gynes). Colonies are called superorganisms because the ants seem to work together as one unit.

Ants have spread across almost all of the land on Earth. The only places without indigenous ants are Antarctica and a few remote or harsh islands. Ants do best in warm, wet tropical areas. Together, they may outweigh the biomass of wild birds and mammals. Their success has been linked to how well they organise themselves, how they can adapt to new places, use resources, and defend themselves. Over a long time of co-evolution with other species, ants have formed mimetic, commensal, parasitic, and mutualistic relationships.

Ant societies show division of labour, communication between individuals, and an ability to solve complex problems. These similarities to human societies have long interested people and been studied closely. Many human cultures use ants in cooking, medicine, and ceremonies. Some species are valued as biological pest control agents. However, their ability to use resources can bring them into conflict with people, because they can damage crops and invade buildings. Some species, such as the red imported fire ant (Solenopsis invicta), Linepithema humile, Wasmannia auropunctata, Anoplolepis gracilipes, and Pheidole megacephala, are seen as invasive species in other parts of the world. They became established there after being brought in by accident.

Etymology

The word ant and the old word emmet come from ante and emete in Middle English. Those words came from ǣmette in Old English. They are related to words in Low Saxon, such as e(e)mt and empe, to emeta in Old Saxon, and to German Ameise, which came from āmeiza in Old High German. All of these words come from a West Germanic word, ǣmaitjōn, which originally meant "the biter." That word is built from a Proto-Germanic root meaning "off, away" and another meaning "cut."

The study of ants is called myrmecology. That name comes from the Ancient Greek word mýrmēx, meaning "ant." Scientists have suggested that a Proto-Indo-European word, *morwi-, was the root of many words for ant. These include Sanskrit vamrah, Greek mýrmēx, Latin formīca, Old Church Slavonic mraviji, Old Irish moirb, Old Norse maurr, Dutch mier, Swedish myra, Danish myre, Middle Dutch miere, and Crimean Gothic miera.

Taxonomy and evolution

The family name Formicidae comes from the Latin word formīca, meaning "ant". This word also gave rise to the words for ant in other Romance languages. Ants belong to the order Hymenoptera, which also includes sawflies, bees, and wasps. Ants evolved from a group within the stinging wasps. A 2013 study suggests they are a sister group of the Apoidea. A more detailed classification was proposed in 2020. Three species of the extinct mid-Cretaceous genera Camelomecia and Camelosphecia were placed outside the Formicidae, in a separate clade within the superfamily Formicoidea. A 2021 study by Fernández and colleagues suggests that the common ancestors of ants and apoids may have existed as early as the end of the Jurassic period.

Vulcanidris, one of the earliest ants ever known from the Early Cretaceous

In 1966, E. O. Wilson and his colleagues identified the fossil remains of an ant (Sphecomyrma) that lived in the Cretaceous period. This ant was trapped in amber dating back to around 92 million years ago. It had features found in some wasps but not in modern ants. The oldest ant fossils date to the mid-Cretaceous, around 113–100 million years ago. They belong to extinct stem-groups such as the Haidomyrmecinae, Sphecomyrminae, and Zigrasimeciinae. Modern ant subfamilies appeared towards the end of the Cretaceous, around 80–70 million years ago. Ants spread and changed a lot during the Angiosperm Terrestrial Revolution. By around 60 million years ago, they had become one of the most common kinds of animal on land. Some groups, such as the Leptanillinae and Martialinae, are thought to have come from early ants. Those early ants were likely hunters that lived under the soil. During the Cretaceous, a few simple ant species spread widely across the Laurasian supercontinent, which is now the Northern Hemisphere. They were still only a small part of the insects from that time. Ants became dominant after adaptive radiation at the start of the Paleogene period. By the Oligocene and Miocene, ants made up a large share of the insects found in major fossil deposits. Only a small number of the ant genera that lived in the Eocene epoch still survive today. Many of today's ant genera can be found in Baltic amber and Dominican amber fossils. Termites live in colonies and are sometimes called "white ants", but they are only distantly related to ants. They belong to the sub-order Isoptera, which together with cockroaches forms the order Blattodea. Blattodeans are related to mantids, crickets, and other winged insects that do not undergo complete metamorphosis. Like ants, termites are eusocial with sterile workers. However, they differ greatly in how they reproduce. Their similar social structure is thought to have developed separately, through convergent evolution. Velvet ants look like large ants but are actually wingless female wasps.

Distribution and diversity

Ants live in almost every part of the world. They are found on all continents except Antarctica. Only a few large islands, such as Greenland, Iceland, parts of Polynesia and the Hawaiian Islands, have no ants of their own. Ants live in many kinds of ecological niches. They eat many different foods. Some eat plants, some hunt other animals, and some clean up dead matter. Most ants are generalists, which means they eat a mix of foods. A few eat only certain kinds. Ants are most common in warm, wet tropical areas, where there can be almost six times as many as in less suitable places. In 2009, E. O. Wilson, an expert on ants, estimated that between one and ten quadrillion (short scale) ants (between 10¹⁵ and 10¹⁶) were alive at any one time. He suggested that their total biomass was about equal to that of all humans. A more careful study in 2022 found that ants make up about 20% of the total human contribution to the world's dry carbon. This is more than wild birds and mammals combined. That study gave a cautious estimate of about 20 × 10¹⁵ (20 quadrillion) ants.

Ants range in size from 0.75 to 52 millimetres. The largest species is the fossil Titanomyrma giganteum. Its queen was 6 cm long, with a wingspan of 15 cm. Most ants are yellow, red, brown or black, though a few are green. Some tropical species have a metallic lustre. More than 13,800 species are known so far, and there may be up to about 22,000 (see List of ant genera). They are most varied in the tropics. Scientists continue to study how ants are classified. Online databases such as AntWeb and the Hymenoptera Name Server help track known and newly described species. Because ants are easy to collect and study in ecosystems, they are useful as indicator species in biodiversity studies.

Region	Number of species
Neotropics	2,162
Nearctic	580
Europe	180
Africa	2,500
Asia	2,080
Melanesia	275
Australia	985
Polynesia	42

Morphology

Ants look different from other insects. They have elbowed antennae, metapleural glands, and a pinch in the second abdominal segment that forms a small node called a petiole. An ant's body has three parts, called tagmata: the head, mesosoma, and metasoma. The petiole makes a narrow waist between the mesosoma (the thorax and the first abdominal segment) and the gaster. Like other arthropods, ants have an exoskeleton, a hard outer covering that protects the body and gives muscles something to pull against. Vertebrates, such as humans, have bones inside their bodies instead. Ants do not have lungs. Gases such as oxygen and carbon dioxide pass through tiny openings called spiracles. Ants also do not have closed blood vessels. Instead, a tube along the top of the body pushes haemolymph toward the head. The nervous system has a ventral nerve cord with ganglia that reach into the body and legs.

An ant's head holds many sensory organs. Ants have compound eyes made of many tiny lenses. They are good at noticing movement, but they do not see a sharp picture. Three small ocelli on top of the head sense how bright it is and the direction of light. Most ants see less clearly than vertebrates, and some subterranean kinds are completely blind. However, Australia's bulldog ant has excellent vision. It can judge the distance and size of objects moving nearly a meter away. Two antennae detect chemicals, air currents, and vibrations. Two strong mandibles carry food, handle objects, build nests, and defend the colony. The wings and six legs attach to the mesosoma. Each leg ends in a hooked claw that helps ants climb. Only reproductive ants, queens and males, have wings. Queens shed their wings after the nuptial flight, leaving visible stubs. A few species have wingless ergatoids and males. The metasoma (abdomen) holds important organs. Many workers have egg-laying structures that have changed into stings. They use these stings to subdue prey and defend their nests.

In a few ant species, workers come in different sizes. These are called minor (micrergates), median, and major ergates (macrergates). Larger ants often have much bigger heads and stronger mandibles. Weaver ants have a clear split between small and large workers, while other species vary more gradually. Workers cannot mate. However, because of the haplodiploid sex-determination system, workers of some species can lay eggs that become males. In some species, such as honeypot ants, young workers are fed until their gasters swell. They then act as living food stores, called repletes. Repletes develop in the North American honeypot ant Myrmecocystus mexicanus. This polymorphism shows flexibility, because other workers can become repletes if these are removed. Differences between worker castes in Acromyrmex sp. are genetic. In Solenopsis invicta, a difference in a single gene can decide whether a colony has one queen or many. The Australian jack jumper ant (Myrmecia pilosula) has just one pair of chromosomes, which makes it an interesting subject for studying social insects. Genome size is a basic characteristic of an organism. Ants have tiny genomes. These may have changed through loss and gain of non-coding regions, mainly transposable elements, and sometimes whole genome duplication. This may be linked to colonisation, but more studies are needed.

Life cycle

An ant's life starts as an egg. If the egg is fertilized, the baby will be a female diploid. If not, it will be a male haploid. Ants grow through complete metamorphosis. In this process, the larva stage is followed by a pupal stage before the ant becomes an adult. Larvae cannot move much, so workers feed and care for them. Workers feed larvae through trophallaxis, where an ant regurgitates liquid food stored in its crop. Adults share food this same way, using a "social stomach." Older larvae may also get solid food, such as trophic eggs, pieces of prey, and seeds. Larvae go through four or five moults before becoming pupae. Unlike a butterfly pupa, an ant pupa has its limbs free and not joined to its body. In some species, food affects whether a young ant becomes a queen or a worker, or which of the different castes of worker it becomes. Genes and surroundings also play complex roles, through control of gene expression. Scientists are still studying this. Winged males, called drones, come out of the pupae along with the winged females that will breed. Some species, such as army ants, have queens without wings. Larvae and pupae need fairly steady temperatures, so workers often move them between brood chambers.

Winter ant (Prenolepis imparis) mating, the drone is much smaller than the queen

A new worker spends its first days caring for the queen and young. Then it digs and does other nest work. Later, it defends the nest and looks for food. These changes can be sudden and are called temporal castes. This age-based job sharing, or polyethism, may have developed because foraging and defence are risky. In the Brazilian ant Forelius pusillus, workers seal the nest entrance from the outside at sunset each day to protect the colony from predatory ants. Ant colonies can live a long time. Queens can live up to 30 years, workers live 1 to 3 years, and males live only a few weeks. In cooler places, ants survive winter by hibernation. Some larvae enter a resting state called diapause. Many species can reproduce without mating, through thelytokous parthenogenesis. Most species allow only queens and breeding females to mate. Some nests have several queens, and others have none. Workers that can reproduce are called "gamergates." In some species, females can use sperm parasitism. In 2025, Messor ibericus queens were shown to lay eggs that grew into workers matching a different species, Messor structor, after they used sperm kept in their spermatheca. This reproductive mode is called "xenoparous," meaning one species produces offspring of another species. Drones in some species, such as army ants, can enter a foreign colony and mate with its queens. They release a mating pheromone when first attacked. Males can also mark invaders with a pheromone after grabbing them and piercing their exoskeleton. Most ants are univoltine, producing one new generation each year. Winged females and males, known to entomologists as alates, leave the colony in a nuptial flight. This usually happens in late spring or early summer, when it is hot and humid. Males often fly first and gather at landmarks such as a pine tree. There, they release a mating pheromone that females follow. Some Cardiocondyla species have both winged and wingless males. In C. elegans, workers may carry new queens to other nests so they can mate with unrelated males. In Hypoponera opacior, wingless queens mate inside the nest. Then they leave with some workers to start a new colony. Mated females break off their wings and begin laying eggs. The first workers, called nanitics, start serving the colony right away. Some species use a process similar to swarming in honeybees to found new colonies.

A typical ant colony lives in one nest with one or more queens. More than 150 species in 49 genera have colonies spread across several nests. Food and workers move between them. Workers recognize their own colony through a mix of body surface chemicals, called cuticular hydrocarbons, which form the colony's smell. In the Argentine ant, Linepithema humile, workers from many nearby colonies accept each other.

Behaviour and ecology

Relationship with humans

Ants do many helpful jobs for people. They help control pest populations and mix the soil. Scientists estimate that ants move a large amount of soil to the surface each year through bioturbation. In southern China, weaver ants have been used in citrus growing. This is considered one of the oldest known uses of biological control. Ants can also be a nuisance when they invade buildings or cause money losses. About nineteen species are listed as "invasives" by the IUCN. Some ants are pests. Their trophallaxis can spread poison from bait to other members of a colony. Some ants are also used in other ways. In parts of Africa and South America, large army ants have been used as surgical sutures. Some ants have toxic venom and are of medical importance. In South Africa, black ants help gather the seeds of rooibos, a plant used for herbal tea. The Sri Lankan relict ant and Adetomyrma venatrix are in danger of disappearing.

Weaver ants are used as a biological control for citrus cultivation in southern China.

Ants and their larvae are eaten in different parts of the world. In Mexico, escamoles are ant eggs and are considered a special food, sometimes called insect caviar. In Thailand, weaver ant eggs and larvae are used in a Thai salad. Ants are also used in science and culture. Scientists who study ants, called myrmecologists, learn about them in laboratories and in nature. Ants are model organisms for research. Ants have also inspired computer science and robotics through Ant colony optimization and Ant robotics. In stories and fables, ants often represent hard work and working together, as in the Aesop fable The Ant and the Grasshopper. Ant farms were once popular educational toys in the United States, as described in the section on ant farms.