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 unified entity. Ants have colonized almost every landmass on Earth. The only places lacking indigenous ant species are Antarctica, Greenland, Iceland, parts of Polynesia, the Hawaiian Islands, and other remote or inhospitable 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.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 pre 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 more transitory, surviving 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
