A swarm is a large group of insects, animals, or people moving together in a dense, active mass. When thousands of bees leave their hive together to find a new home, they form a buzzing cloud called a swarm. Locusts travel in swarms so enormous they can darken the sky and devour entire fields of crops in hours.

The word captures both the size of the group and its energy: a swarm doesn't sit still. Ants swarm over a dropped piece of candy at a picnic. Fish can swarm in huge schools that twist and turn together as one. Even people can swarm: fans might swarm onto a field after a championship victory, or shoppers might swarm into a store on the first day of a big sale.

Scientists who study swarms have discovered something fascinating: even though no single bee or bird is in charge, swarms move with surprising coordination. Each member follows simple rules, yet together they create complex patterns that no individual could create alone.

As a verb, to swarm means to move or gather in such a group: reporters swarmed the astronaut after her return from space, or protesters swarmed around a government building.