|Meat eater ant feeding on honey|
Ants form colonies that vary greatly in size. Some species have a few dozen predatory individuals living in small natural cavities. Some highly organised colonies may cover large territories and have millions of individuals. Ants are usually small, but can carry the weight of twenty ants. Worker ants carry food back to the colony so that other ants and the queen can eat.
The following account is mainly about ants which live in large colonies.
A colony has a female reproductive ant, called a queen, who lays eggs. Those eggs will hatch into worker ants. Larger colonies of ants having millions of ants mostly have female ants making groups of workers, soldiers, or other special castes. Almost all ant colonies also have some fertile male ants called drones.
These colonies are sometimes described as 'superorganisms' because the ants appear to operate as a unified entity, collectively working together to support the colony.
Phylogenetic analysis suggests that ants arose in the Lower Cretaceous period about 110 to 130 million years ago, or even earlier. One estimate from DNA studies places the origin of ants at ≈140 million years ago (mya). Another study puts it in the Jurassic at 185 ± 36 mya (95% confidence limits).
After the rise of flowering plants about 100 million years ago ants diversified. They became ecologically dominant about 60 million years ago.
During the Cretaceous period, a few species of primitive ants ranged widely on the Laurasian super-continent (the northern hemisphere). They were scarce in comparison to other insects, representing about 1% of the insect population.
Ants became dominant after adaptive radiation at the beginning of the Cainozoic. 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, approximately one in ten 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).
Termites, though sometimes called white ants, are not ants and belong to the order Isoptera. Termites are actually more closely related to cockroaches and mantids. Termites are eusocial but differ greatly in the genetics of reproduction. The similar social structure is attributed to convergent evolution. Velvet ants look like large ants, but are wingless female wasps.
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).
Like other 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 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 pumps haemolymph toward the head, thus driving the circulation of the internal fluids.
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 and polarization. Compared to vertebrates, most ants have poor-to-mediocre eyesight and a few subterranean species are completely blind. However, some ants, such as Australia's bulldog ant, have excellent vision and are capable of discriminating the distance and size of objects moving nearly a metre away.
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. In some species, a small pocket (infrabuccal chamber) inside the mouth stores food, so it may be passed to other ants or their larvae.
Both the legs and wings of the ant are attached to the mesosoma ("thorax"). The legs terminate in a hooked claw which allows them to hook on and climb surfaces. Only reproductive ants, queens, and males, have wings. Queens shed their wings after the nuptial flight, leaving visible stubs, a distinguishing feature of queens. In a few species, wingless queens (ergatoids) and males occur.
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.
Development and reproduction
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 larval stages passing through a pupal stage before emerging as an adult. The larva is fed and cared for by workers.
Larvae may also be given solid food brought back by foraging workers, and may even be taken to captured prey in some species. The larvae grow through a series of moults and enter the pupal stage.
The differentiation into queens and workers (which are both female), and different castes of workers, is influenced in some species by the food the larvae get. Genetic influences, and the control of gene expression by the feeding are complex. The determination of caste is a major subject of research.p351, 372
A new worker spends the first few days of its adult life caring for the queen and young. It then does digging and other nest work, and later, defends the nest and forages. 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 that are older and are likely to die soon of natural causes.
Most ant species have a system in which only the queen and breeding females can mate. Contrary to popular belief, some ant nests have multiple queens (polygyny). The life history of Harpegnathos saltator is exceptional among ants because both queens and some workers reproduce sexually.
The winged male ants, called drones, emerge from pupae with the breeding females (although some species, like army ants, have wingless queens), and do nothing in life except eat and mate.
The nuptial flight
Most ants produce a new generation each year. During the species specific breeding period, new reproductives, winged males and females 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 some others they may mate with anywhere from one to ten or more different males. 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 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,p143 a process akin to swarming in honeybees.
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 parthenogenesis, and one species, Mycocepurus smithii is known to be all-female.
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, and survive only a few weeks. Ant queens are estimated to live 100 times longer than solitary insects of a similar size.
Ants are active all year long in the tropics but, in cooler regions, 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
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.
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.
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.
Ants attack and defend themselves by biting and, in many species, by stinging, often injecting or spraying chemicals, such as formic acid in 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.
The sting of jack jumper ants can be fatal, and an antivenom has been developed for it.
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 and 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. Before striking, the ant opens its mandibles extremely widely and locks them in this position by an internal mechanism.
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.
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.
Nests may be protected from physical threats such as flooding and overheating by elaborate nest architecture. Workers of Cataulacus muticus, an arboreal species that lives in plant hollows, respond to flooding by drinking water inside the nest, and excreting it outside. Camponotus anderseni, which nests in the cavities of wood in mangrove habitats, deals with submergence under water by switching to anaerobic respiration.
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 field for navigation. 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 may sometimes turn back on themselves and form a circular ant mill. The workers may then run around continuously until they die of exhaustion.
- See also: Entomophagy
Ants and their larvae are eaten in different parts of the world. The eggs of two species of ants are used in Mexican escamoles. They are considered a form of insect caviar and can sell for as much as US$40 per pound ($90/kg) because they are seasonal and hard to find. In the Colombian department of Santander, hormigas culonas (roughly interpreted as "large-bottomed ants") Atta laevigata are toasted alive and eaten.
In areas of India, and throughout Burma and Thailand, a paste of the green weaver ant is served as a condiment with curry. Weaver ant eggs and larvae, as well as the ants, may be used in a Thai salad, yam, in a dish called yam khai mot daeng or red ant egg salad, a dish that comes from the Issan or north-eastern region of Thailand.
From the late 1950s through the late 1970s, ant farms were popular educational children's toys in the United States. Some later commercial versions use transparent gel instead of soil, allowing greater visibility at the cost of stressing the ants with unnatural light.
An ant trail
The spider Myrmarachne plataleoides (female shown) mimics weaver ants to avoid predators.
Ants may obtain nectar from flowers such as the dandelion but are only rarely known to pollinate flowers.
A meat ant tending a common leafhopper nymph
A weaver ant in fighting position, mandibles wide open
Leaf nest of weaver ants, Pamalican, Philippines
An ant collects honeydew from an aphid
Aesop's ants: picture by Milo Winter, 1888–1956
Ant Facts for Kids. Kiddle Encyclopedia.