Ant is a small insect—usually black, brown, red, or yellow in color—that lives in organized communities called colonies. Ants somewhat resemble termites but can be distinguished by their narrow waists and elbowed (bent) antennae. Because ants depend on their colonies for survival, scientists classify them as social insects. Ants belong to the same order (related group) of insects as bees and wasps.
Ants vary in color and size. Besides black, brown, red, and yellow, they can be orange, blue, green, or even purple. The largest ants measure over 1 inch (2.5 centimeters) long. The smallest ants are about 1/25 inch (0.1 centimeter) long—barely visible to the unaided eye.
Ant colonies differ enormously in size. A colony may have a dozen, hundreds, thousands, or in rare cases, even millions of members. Regardless of size, most ant colonies share the same general structure. A colony usually has one or more queens, females whose chief job is to lay eggs. The rest of the colony consists mostly of workers. These wingless female ants do not lay fertile eggs but instead build the nest, search for food, care for the queen and the young, and protect the colony. Unlike queens, workers commonly leave the nest and can often be seen walking about on the ground or in trees. An ant colony also includes the ant young or larvae. The wormlike larvae hatch from eggs laid by the queen. Male ants, who have wings, live in the colony only at certain times of the year. Their only job is to mate with young queens, who also have wings.
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Scientists have identified more than 10,000 ant species, and they name new species every year. Most experts estimate that 20,000 to 30,000 ant species exist. Ants live almost everywhere on land, except in extremely cold areas. Most inhabit regions with warm climates, including deserts. Mild regions of Europe, North America, Japan, and China also have large ant populations. Some ant species live in underground tunnels, and some build earthen mounds. Others live inside trees or in hollow parts of certain other plants. Still other species construct their nests from tree leaves. Some ants do not build permanent nests.
Scientists think that ants gradually developed from wasp ancestors over 100 million years ago. Ants closely resemble wasps in the structure of their bodies. However, an ant has a node (knotlike growth) on top of its waist that distinguishes it from most antlike wasps.
The bodies of ants
Among most ant species, the queens, workers, and males differ in size. In many cases, the queens grow several times larger than the workers. The males usually appear larger than the workers, but smaller than the queens. The workers of a particular species may also differ in size. Scientists call the largest workers soldiers.
Like all insects, ants have a hard, shell-like covering called an exoskeleton that protects their internal organs. An ant’s muscles attach to the inside of the exoskeleton.
An ant’s body features three main sections: (1) the head, (2) the thorax, and (3) the abdomen. The internal organs and sense organs of an ant resemble those of many other insects.
The head
of an ant has the antennae, eyes, and mouthparts. The mouthparts include the mandibles and the maxillae. The mandibles consist of a pair of jaws attached to the front of the head that move from side to side rather than up and down. Ants use them to grasp food, carry their young, construct nests, and fight enemies. A pair of maxillae lie behind the mandibles and enable an ant to chew food into small particles. The ant then laps up the particles with its tongue and passes them into a small pouch inside the mouth. Muscles that line the pouch contract, squeezing liquid food out of the solid particles. Ants swallow the liquid and spit out the remaining solids as a pellet. They sometimes feed this pellet to larvae, who process it into liquid food.
Each of an ant’s maxillae has a comb, which consists of a row of tiny hairs. An ant cleans its front legs by drawing them across the combs.
The thorax
is the middle section of an ant’s body. Among most species, the males and young queens have two pairs of wings attached to the thorax. The thorax holds the muscles that enable ants to beat their wings and fly at mating time. Worker ants do not have wings.
An ant has six legs attached to the underside of the thorax. Each leg consists of nine segments connected by movable joints. The foot of each leg has two hooked claws that dig into a surface as an ant walks. The claws enable ants to climb trees, walk on the undersides of tree limbs and leaves, and tunnel underground.
The abdomen
is the rear section of an ant’s body. It includes the narrow waist, also called the pedicel, and a bulblike hind part called the gaster. The waist consists of one or two movable, beadlike segments that connect the thorax to the gaster. In ants with one such segment, the waist is called the petiole. In ants with two, the second segment, closest to the gaster, is called the postpetiole. Some ants have a sting at the tip of the gaster that they use to defend themselves.
Internal organs.
A nerve cord extends from the ant’s head through the thorax and abdomen. It connects the brain to nerves throughout the body.
Ants have a simple heart shaped like a long tube. The tube extends from the head to the rear of the gaster. Muscle contractions force the blood through the tube toward the head. The blood empties out of the tube near the brain. An ant does not have blood vessels. Instead, the blood flows from the head back through the body cavity, bathing all the tissues and organs. It then reenters the tube through small openings along the sides. The openings have valves that allow blood to enter the tube but prevent it from leaking out.
Ants do not have lungs. Instead, they have many air tubes that branch out to all parts of the body. Oxygen enters the tubes through tiny openings along the sides of the body called spiracles. Carbon dioxide passes out of the body through the spiracles as well.
An ant’s digestive system consists of a tube that extends from the mouth to the end of the gaster. This tube connects the insect’s two stomachs, both in the gaster. The first stomach, called the crop or social stomach, stores liquid food without digesting it. The crop can expand greatly to hold food. An ant frequently regurgitates (spits up) some of the stored food and shares it with other ants. A valve separates the crop from the ant’s second stomach. When the ant is hungry, it moves food from the crop to the second stomach for digestion.
Sense organs.
An ant’s chief sense organs are its antennae. Ants have two antennae attached to the front of the head. The antennae serve as organs of smell, touch, and taste. When an ant engages in activity, its antennae move constantly. Ants use their antennae to feel the ground, detect scents in the air, examine food, and stroke one another. Antennae also help ants to find their way about, search for food, and recognize nestmates, who share a similar odor.
Ants have taste organs on their mouthparts in addition to those on the antennae. These taste organs lie between the mandibles. Ants have touch organs not only on the antennae but also on almost all other parts of the body. The touch organs consist of tiny hairs and spurs.
Most ants have two compound eyes, one on each side of the head. A compound eye consists of tiny lenses set close together. The number of lenses varies from 6 to more than 1,000, depending on the ant species. Usually, the males and queens have more lenses than the workers do. Each lens sees only a small part of whatever an ant looks at. Impressions from all the lenses together form a picture composed of tiny bits. Compound eyes enable ants to see movements easily. However, ants can clearly see only nearby objects. In addition to compound eyes, some ant species have three simple eyes, called ocelli, on the top of the head. Ocelli can sense only light or dark. Some ants that live their entire lives underground have no eyes.
Ants lack ears, but they can detect vibrations by means of sense cells called chordotonal organs on their antennae, legs, and body. These organs register vibrations that pass through the ground or other solid material. Researchers do not know for certain whether ants can hear sounds that pass through the air.
Some ants can make sounds by means of a stridulatory organ on the abdomen. In most cases, this organ consists of a row of ridges on one segment of the abdomen and a hard point on another segment. Ants make squeaky or buzzing sounds by rubbing the segments together, much as a person might make noise by running a fingernail over the teeth of a comb. Some ant sounds can be heard by people.
Life in an ant colony
All ants live in groups, but different ant species vary in their ways of life. This section discusses the general features of life in an ant colony. The section Kinds of ants describes some of the many ways of life among ants.
Castes.
Most ant colonies share the same basic structure. It divides the colony into three distinct castes (classes): (1) the queen, (2) the males, and (3) the workers.
In most cases, a young queen starts a new colony after mating with one or several males. After establishing a colony, the queen lays eggs for the rest of her life. The other ants protect, feed, and tend the queen because her eggs help ensure the survival of the colony. However, the queen does not “rule“ the colony. Some colonies have only one queen. However, in some species, thousands of queens may reside in a single colony.
Males do not do any work in the colony. They live only a short time, and their only purpose is to mate with young queens.
The workers feed and lick the queen, as they do one another. Besides caring for the queen, the workers enlarge, repair, clean, and defend the nest; care for the young; gather food; and even remove dead or sick ants from the colony. A worker may do chiefly one job all its life or may change jobs from time to time.
The workers among many species of ants vary in size and shape but are always female. The largest workers, the soldiers, have a big head and large mandibles. In some species, the soldier’s chief job is to defend the colony. Among certain carpenter ants, ants that nest in wood, the soldiers have a blunt, plug-shaped head. These soldiers serve as doorkeepers. To keep enemies out, the soldier blocks a tunnel with its head. The soldier will stand aside to allow a nestmate to pass, recognizing the member by its odor. Among harvester ants, ants that collect seeds for food, the soldiers crack open the seeds that smaller workers collect. The small workers then feed on the soft, inner contents of the seeds.
Nests.
Most ant species make their nests underground by carving tunnels and chambers in the soil. Some of these species build large mounds of soil, twigs, and pine needles over their underground nests.
Many ants nest in other places. For example, carpenter ants make nests in the trunks and branches of trees and in the wooden beams of houses. These ants, unlike termites, do not eat wood. They chew tunnels in wood only to make nesting space. Other kinds of ants make their homes beneath the bark of trees, in hollow twigs, or in the thorns of certain plants. Some species chew up plant fibers and use the material to make “cardboard” nests. Ants may even nest in old acorns and hickory nuts that beetles have hollowed out.
Tropical weaver ants construct nests from tree leaves. Some workers hold the edges of leaves together, while other workers carry silk-spinning larvae back and forth across the edges. The result is a thick sheet of silken webbing that binds the edges of the leaves together.
Most ant nests consist of many chambers. One chamber houses the queen and her eggs. Other chambers serve as “nurseries” in which the workers keep the immature ants. Ants move their young among chambers to keep them at the ideal temperature and humidity. Workers gather and rest in other chambers. The nests of some ants have rooms for storing food or growing fungi for food. As a colony grows, the workers enlarge the nest by constructing more chambers and passageways. Ants that live in regions with cold winters move to the deepest parts of their nests during that season.
Reproduction.
Many queens lay thousands of eggs in a lifetime. Most eggs develop into workers. Some become males and young queens that leave the nest a few weeks after reaching adulthood. These ants go on a mating flight. They fly in a swarm high in the air and mate.
During mating, a male deposits sperm inside a queen’s body. A young queen may mate with one or more males. She receives her lifetime supply of sperm during the mating flight and stores it in her gaster. The sperm later enter her eggs as she lays them.
After mating, the male and queen land on the ground. The male wanders off and dies. The queen removes her wings by knocking them off with her legs, pulling them off with her jaws, or rubbing them against a nearby object. She then begins to search for a nesting site. Sometimes, newly mated queens do not begin a new colony but rather become members of an existing colony of the same species or return to their original colony. In other cases, two or more unrelated queens may start a colony together. Among parasitic ants, the queen takes over the nest of another ant species, called the host. She then rids the colony of its queen and depends on the host workers to care for her and her eggs. However, among most ant species, the queen establishes a new nest.
After the queen prepares a nest, she seals the entrance. She soon begins to lay eggs. The queen primarily lives off her body fat during this time. Her now useless wing muscles dissolve into nourishing substances that enter the bloodstream and provide her with energy. She may also eat some of her eggs. Queens of most species do not leave the nest to search for food.
Ants go through four stages of development: (1) egg, (2) larva, (3) pupa, and (4) adult. The small size of ant eggs makes them difficult to see without a microscope. They hatch within a few days and become larvae. The white, wormlike larvae cannot move, and the workers often carry them around in their jaws. The larvae lack legs, but they have a head and a mouth. The queen feeds her first larvae with her saliva and sometimes with her eggs. The larval stage usually lasts a few weeks. After the larvae complete their growth, they become pupae. The larvae of some species spin a fine silk cocoon around themselves before becoming pupae. In other species, only a tough layer of transparent skin covers the pupae. The pupae lie motionless and do not eat. Over a period of one to several weeks, the pupae transform into adult ants, which emerge from the cocoon or skin.
Larvae play a vital role in feeding most colonies because they alone can process solid food. The workers feed them solids, and the larvae regurgitate a nutritious fluid used to feed other members of the colony.
The first worker ants to become adults leave the nest and bring back food for the queen. They take over the care of the brood—the eggs, larvae, and pupae—and the queen continues to lay eggs. As the colony increases in size, it produces more young queens and males who leave the nest to mate and repeat the cycle.
Protection against enemies.
Anteaters, birds, frogs, lizards, spiders, toads, and many insects prey on ants. In most cases, ants from different colonies, even those from the same species, treat one another as enemies.
About half of all ant species have a sting that serves as an effective defense against other insects. The sting releases a poison that can damage or destroy tissue. Some ants that lack a sting can spray poison from the tip of the gaster. Ants can only defend themselves against larger predators by attacking in a massive swarm.
Battles between worker ants from different colonies occur often. Sometimes these battles do not result in serious injuries. For example, honey ants, ants that collect and store liquid food, often engage in shoving matches between workers from rival colonies. The workers do not hurt one another, but the victors sometimes take over the nest of the defeated colony. Some ants fight huge, grim wars in which thousands of ants kill one another. The ants may use their jaws to grab enemies by a leg or an antenna. Often, several nestmates grab the legs and antennae of an enemy ant and hold the victim stretched out. Other nestmates may join the fight and tear the victim apart with their jaws. The winners may invade the nest of the defeated colony and carry off the brood, which they eat. Certain ant species live entirely by robbing the nests of other ants in this way.
Communication.
Coordinating the activities of an ant colony requires efficient methods of communication. The release of chemicals called pheromones serves as the basic means of communication among ants. An ant’s body contains about a dozen glands that open at certain places in the head, thorax, and abdomen. These glands produce pheromone signals that other ants can smell and taste, enabling nestmates to communicate. The various kinds of pheromones communicate different information. By releasing pheromones from the tip of the gaster, for example, an ant may lay a scent trail from a new food supply to its nest. Nestmates then follow the trail to the food. To immediately warn nestmates of danger, ants can release airborne “alarm” pheromones.
Ants recognize nestmates by their familiar odor. When two ants meet, they smell each other with their antennae. Ants can even distinguish between the different castes within the colony and identify the queen by her unique chemical signals.
Ants also communicate by touch and vibrations. Ants that live inside plants or in leaf nests may tap their gasters against the outside walls of the nest when they discover food or an enemy nearby. The taps send vibrations through the nest walls to alert the ants inside. Ants with a stridulatory organ arouse their nestmates by producing squeaky or buzzing sounds.
Life span.
Among insects, ants have a long life span. Queens, workers, and males live for different lengths of time. Queens live the longest, usually from about 5 to 15 years. However, some queens have lived more than 20 years. Workers live from less than 1 year to more than 5 years. Males live only a few weeks or months before the mating flight and die soon after mating.
Kinds of ants
Entomologists (scientists who study insects) sometimes group ants according to their ways of life, which vary greatly. This section discusses six groups of ants that live in different ways. They include: (1) army ants, (2) slave-making ants, (3) harvester ants, (4) dairying ants, (5) honey ants, and (6) fungus-growing ants.
Army ants
prey ferociously on insects and spiders. Some feed primarily on other ants and their young. While most species of army ants travel across the land in narrow columns, some species in desert regions live primarily underground. Army ants live in immense colonies numbering from 10,000 to several million members. Each colony includes a single large queen. Army ant colonies do not build permanent nests but instead establish temporary nests called bivouacs.
Many army ant species follow complex patterns of movement based around the reproductive cycle. In one common pattern, the colony remains in the same location for two to three weeks while the queen lays thousands of eggs. Once the eggs hatch, the colony has many hungry larvae to feed. At that time, the colony migrates to a different bivouac nearly every night and sends out raiding columns of worker ants to hunt for food for the young. This period of migration (wandering) continues until the larvae mature into pupae and no longer require feeding. The demand for food within the colony drops suddenly, and the colony remains in a single location for a couple of weeks while the pupae complete their development into adult ants. During this time, the colony sends out small raids to secure food, and the queen lays a new batch of eggs. The pupae and the newly laid eggs hatch at about the same time, and the colony begins another cycle of migration in search of food for the larvae.
Most army ants inhabit the tropical regions and rain forests of Central America, South America, Africa, and Asia. However, some species live in milder climates in North America. Army ants generally do not present a danger to people or large animals, though their sting is extremely painful.
Slave-making ants
invade the nests of other ants, kidnap the pupae, and bring them back to the invaders’ colony. When the pupae develop into adults, they act as members of the slave-making colony. The “slaves” help to build the nest, care for the young, and hunt for food.
Some kinds of slave-making ants depend on slaves for their survival. For example, Amazon ants have long, curved, swordlike mandibles that serve well for fighting and carrying home pupae but interfere with hunting and eating, digging nests, and caring for young. These ants rely on slaves to perform these tasks.
After the mating flight, the young slave-making queen takes over the nest of a slave species to establish a new colony. She kills or drives away many of the colony’s workers and their queen. The slave-making queen then stays with the colony’s brood until some of them reach adulthood. These new worker ants treat the slave-making queen as they would their own queen. They care for her eggs, which develop into slave-making adults, who will raid other nests and bring back more slaves. Slave-making ants most commonly live in the cool regions of North America, Europe, and Asia.
Harvester ants
collect seeds and store them in special chambers in their nests. In doing so, they always have a supply of food available in case food outside the nest becomes scarce. The ants remove the husks from the seeds and chew the kernels into a soft paste called ant bread. They feed this paste to one another and to their young. Most harvester ants will also eat insects when available, especially termites.
Harvester ants live throughout much of the world, primarily in deserts and other regions with a distinct dry season. They build their nest in exposed areas in the form of a mound.
Dairying ants
live chiefly on a sugary liquid called honeydew produced by other insects. In addition to sugar, honeydew contains small amounts of protein and other nutrients. Dairying ants obtain honeydew from insects that suck juices from plants. These juices contain more sugar and water than the insects need, and they discharge the excess as honeydew. Dairying ants visit the plants on which the insects feed so that they can lick up the honeydew. In most cases, the insect will wait for an ant to come by and “milk” it before releasing its honeydew. The ant does so by stroking the insect with its antennae. The best-known dairying ants feed on aphids (plant lice). Other ants obtain honeydew from scale insects called mealy bugs or other insect species.
Many dairying ants collect the eggs of aphids and store them in their nests in winter. When spring arrives, the eggs hatch, and the ants carry the aphids out of the nest and place them back on plants. The ants then begin to collect honeydew from the aphids again.
Certain species of dairying ants tend underground “herds” of aphids that feed on plant roots inside the ant nest. Among these species, the young queen carries an egg-laying aphid between her jaws when she leaves the nest to go on the mating flight. After the queen digs her new nest, she places the aphid on a root and starts a new herd. Other species of dairying ants tend aphids aboveground on stems, leaves, and flowers.
Dairying ants protect honeydew-producing insects by fighting off predators. Because the insects they protect can feed on crops and cause great damage, farmers consider dairying ants to be agricultural pests.
Honey ants,
also called honeypot ants, gather honeydew from aphids and other insects or directly from plants and store it in their nests. Inside the nest, certain workers, called repletes, serve as living storage tanks for the colony. After returning to the nest, the workers that gather the honeydew feed it to the repletes. The replete stores the food in its crop. Over time, the gaster of the replete becomes so swollen with honeydew that the ant cannot walk. It hangs motionless from the ceiling of a special chamber in the nest. The replete feeds its nestmates by regurgitating some honeydew whenever a nestmate taps it with its antennae. Honey ants most commonly inhabit deserts and other dry, warm regions, particularly in Australasia and North America.
Fungus-growing ants
cultivate gardens of fungi in their nests. Each colony of fungus growers raises one particular type of fungus. The fungi grow tiny, nourishing knobs that provide the ants with their only source of food. The ants in a colony fertilize their garden with plant materials—including seeds and parts of flowers and leaves—that they gather from outside the nest. Some fungus growers use insect waste, such as caterpillar droppings, for fertilizer. The ants tend carefully to their garden, controlling the temperature and humidity in the nest and removing fungi that may grow as weeds. The ants also produce chemicals in their glands that they can apply to the garden to prevent the wrong fungi from taking over. When a young fungus-growing queen leaves the nest to mate and establish a new colony, she carries a little pellet of fungus in a special chamber under her head. After the queen prepares her nest, she starts a new garden with the pellet. Most fungus growers reside in the tropical and subtropical regions of North and South America.
Perhaps the best known fungus growers are the leaf-cutter ants. These ants build huge underground nests in which millions of ants may live. At night, they send out columns of workers to cut pieces of leaves from trees, shrubs, and other plants. The workers carry the leaf fragments back to the nest, holding them over their heads. The ants look as though they are carrying parasols, and so people sometimes call them parasol ants or umbrella ants. Inside the nest, the ants chew the leaf fragments to a pulp, which they use to grow fungi. In parts of Central and South America, leaf-cutters cause severe damage to crops by stripping away their leaves. For example, in Brazil, colonies of leaf-cutter ants sometimes strip all the leaves from an orange grove in one night. 
Keeping an ant farm
You can study a colony of ants as they work, eat, and care for their young by keeping an artificial nest called an ant farm. An ant farm consists of a container made of transparent plastic or glass through which you can view the chambers of the ants’ nest. You can purchase a commercial ant farm that comes with a certificate to exchange for live ants. To help prevent the spread of nonnative ant species, many countries prohibit the shipping of queen ants in the mail. For this reason, the ants you receive will likely consist entirely of workers. Without a queen to lay eggs, your ant colony will not last long. The worker ants will only live for a month or two.
You can also make your own ant farm. A large, clean glass jar or plastic container with clear sides and a lid makes the simplest ant farm. First, fill the jar with slightly wet soil and pack the soil down lightly. Next, collect the eggs, larvae, pupae, and ants from a single colony. This will take some practice and skill. You can find ant colonies under rocks or by digging up a nest in the soil. You may recognize the colony’s queen by her large size. Gather the ants in a plastic bag. Then put the bag of ants in the refrigerator for half an hour to slow them down, which will help you transfer them to the jar more easily. Once the ants have dug a nest in the jar, they will become less eager to leave and easier to observe. Ants typically need little or no light, so wrap dark paper around the walls of the jar to keep out the light. Take the paper off only when you wish to watch the ants. However, you may allow light to pass through the top of the jar. When handling the jar, be careful not to shake it.
Feed the ants every few days with a little honey mixed with water and soaked into a cotton ball. You may also feed them small pieces of nuts, dead insects, and cookie crumbs, among other things. You may be surprised to learn all of the things that ants will eat. Remove unused food from the ant farm promptly, or it will become moldy. Moisten the soil in the jar when it starts to become dry. Do not forget to release the ants outside when you have completed your observations.
The importance of ants
Ants play an important role in the balance of nature. They eat large numbers of insects and keep them from becoming too plentiful. Ants themselves serve as an important food source for birds, frogs, lizards, and many other animals. See Balance of nature.
The activities of ants can both benefit and interfere with agriculture. Some ant species aid farmers by eating insects that damage crops. Ants that dig underground also help to break up, loosen, and mix the soil. In doing so, they enable the soil to absorb water more easily. However, some species, such as dairying ants, protect aphids and other insects that harm crops. Fire ants, stinging ants common in the southern United States, build large mounds that interfere with the cutting of hay.
Some ants act as household pests. For example, carpenter ants damage houses by tunneling through their wooden beams. Pharaoh’s ants and thief ants invade houses, restaurants, and other buildings and eat stored food. Certain species, such as the fire ant, also have a painful sting, which can cause an allergic reaction in some people.
Occasionally, people introduce ant species into areas where the insects do not naturally occur. The ants grow in number and destroy native ants and other insects in the area. Once a nonnative ant species has established itself in an area, getting rid of it becomes difficult.
Ants play an important role in maintaining many ecosystems. An ecosystem consists of a community of living things along with its natural environment. Tunneling by ants adds air to the soil and distributes nutrients (nourishing substances) near plant roots. Ants also consume dead plants and animals and animal wastes and break down fallen leaves and wood. These activities help recycle nutrients and the element carbon, making them available for use by growing plants.
