A large number of insects or other small organisms, especially when in motion. A group of bees with a queen bee in migration to establish a new colony. See Synonyms at flock1. An aggregation of persons or animals, especially when in turmoil or moving in mass: A swarm of friends congratulated him. A number of similar geologic phenomena or features occurring closely within a given period or place: a swarm of earthquakes. To move or emerge in a swarm. To leave a hive as a swarm. Used of bees. To move or gather in large numbers. To be overrun; teem: a riverbank swarming with insects. See Synonyms at teem1. To fill with a crowd: sailors swarming the ship's deck. To climb by gripping with the arms and legs. To climb (something) in this manner.