n. & v.
n. 1 a cluster of bees leaving the hive with the queen to establish a new colony. 2 a large number of insects or birds moving in a cluster. 3 a large group of people, esp. moving over or filling a large area. 4 (in pl.; foll. by of) great numbers. 5 a group of zoospores.
v.intr. 1 move in or form a swarm. 2 gather or move in large numbers. 3 (foll. by with) (of a place) be overrun, crowded, or infested (was swarming with tourists).
[ OE swearm f. Gmc ]