Ants live together in big groups called colonies, and some colonies hold thousands to millions of ants. The queen is the largest ant in the colony and the ant that lays the eggs, and a queen lays thousands of them, while a new queen raises her first workers, and then they take over the work of the nest. Almost all the ants you see are female workers that cannot lay eggs, and these workers find food, groom and carry the young inside the nest, and build and defend the nest. Cooperation in ant colonies is largely self-organized, which means that coordination arises from interactions among individual ants, and the clues that follow show how that works.

Ants do not see very well, so they find their way mostly by smell and touch, and they use their two bent, elbowed antennae to smell and to touch things. They pass messages with smells, touch and vibrations, and in 1959 E. O. Wilson and mathematician William Bossert discovered how ants communicate with chemical signals called pheromones. Ants use these scent chemicals to warn each other of danger or to lead each other to food, and if an ant colony is attacked, ants make alarm chemicals that call other workers to help defend the nest. When an ant finds food, it lays a scent trail on the way home, and the pheromone makes other ants likely to follow the same path, while worker ants carry the food back to the nest.

A team led by Deneubourg tested how a trail can steer a whole colony by giving Argentine ants a bridge with two branches between the nest and the food, with one branch twice as long as the other. Within a few minutes, the colony usually chose the shorter branch. The first ants back at the nest were those that took the shorter path both ways, and that route was marked with pheromone twice first, so nestmates were drawn to it. Simple interactions, such as one ant following another's trail, can together solve hard problems like finding the shortest route to food, and the bridge test is one clear example of how a colony can solve such a problem.

Ants make their nests underground, in mounds, or in trees, and weaver ants build theirs from leaves. A baby ant is called a larva, and weaver ant workers use their own larvae like needles: the larvae make silk that stitches the leaves together to form the nest. To bring the leaves close, the workers form chains, as ants grab the leaf edge, nestmates grab the first ant's body, and the chain together drags and bends the leaf.

When a flood comes, fire ants cling together and float in a group, and a fire ant raft carries the whole colony, with the queen and young in the middle. In water, the ants grip each other with a force 400 times their body weight, making the raft act like a thick, stretchy fluid made of ant molecules. A raft builds itself in less than 100 seconds, and it heals itself: if one ant is removed, others move in to fill the gap. Fire ant rafts can float on water for weeks at a time, and to stay safe from fire ants, stay away from their mounds and from floating rafts of ants.

Ants range in size from tiny to about an inch long, and they eat many different kinds of food, such as nectar, seeds, fungus and insects. They have strong jaws called mandibles that they use to carry things and to cut. Some ants can sting, and all ants can bite, and a fire ant sting can cause burning, itching and swelling. If an ant stings or bites you, tell a grown-up. Trouble breathing or a tight chest after a sting means getting medical help right away.

All ants live in advanced societies with cooperative parenting and division of labor, but their ancestors were solitary wasps. In a healthy fire ant colony the queen lays an average of 800 eggs a day, and the colony can reach 500,000 workers, while a queen ant can live for several years and many workers live only a few months. As of November 2026, about 20 quadrillion ants live on Earth, and about 2.5 million ants live on Earth for every person. An ant colony can act like one living thing, a superorganism, because its members communicate and cooperate. The Gordon lab at Stanford studies ant colonies as systems that work without central control, comparing them to the internet, the immune system and the brain.

Words to know

• colonies: big ant groups
• pheromones: scent chemicals
• raft: floating ant group
• superorganism: one living thing