What Does “A Swarm of Rats” Mean?
“Swarm” is borrowed from insect terminology, usually reserved for bees or locusts, and its use for rats emphasizes the same thing “horde” does: overwhelming numbers appearing seemingly all at once. It’s less a precise behavioral description than an impression, the sense of a space suddenly, alarmingly full of rats, most often associated with a serious infestation rather than a typical, smaller colony sighting.
Genuine large-scale rat swarms tend to show up in specific conditions: abundant, easily accessible food, minimal predation pressure, and enough undisturbed shelter for a colony’s rapid reproductive potential to go largely unchecked over multiple breeding cycles. Urban environments with reliable food waste and extensive underground infrastructure, like sewer and subway systems, have proven especially conducive to this kind of population surge, which is part of why “swarm” so often gets reached for in describing serious urban rat problems specifically.
Example: “Reports described a swarm of rats overtaking the abandoned lot within just a few months of the property going vacant.”
Related: Collective Nouns for Mammals · What Is a Group of Rats Called?