Insects of the family Formicidae.
Ant colonies range in size from a few dozen predatory individuals to highly organized colonies with specialized wingless females arranged in castes ("workers", "soldiers" etc).
Ants are highly successful and have colonized all land masses on Earth excluding Antarctica and a few remote islands. They are also remarkably diverse - especially in tropical regions where they have adapted a range of co-evolutionary relationships with other species. E.O.Wilson (ant specialist and acclaimed author) has estimated the number of ant individuals alive at any one moment as being between one and ten quadrillion.
Ants are easily introduced into an area accidentally, so they include a number of problematic invasive species (e.g. fire ants in the US).
Most ant questions on this site will be pest control questions. How do I remove ants? Should I remove ants? How can I do it without harming kids, pets, and 'beneficial' insects. Ants can pose problems by eating plants (e.g. leaf cutter ants) but are usually a problem due to their stings and their innate ability to find food.
Despite these problems, it should be born in mind that ants can also be beneficial to humans and even gardeners. They suppress more problematic pest populations, help to aerate(aeration) the soil, can act as predators, used to harvest rooibos (South African seeds used to make a herbal tea), and as food. They also have a number of medicinal uses, e.g. army ant mandibles can be used as medical sutures, and some ant venoms have medical uses.