Why would fire ants swarm?

Answer by  melz10 (61)

When a fire ants stings an animal, a pheromone is released and signals other fire ants that danger is near. Depending on the circumstances, fire ants would rather fight than flight and that is when they swarm.

Answer by  PhotoPete (45)

Fire ants are extremely territorial. With that in mind, when their mounds are disturbed by an outsider, like a person accidentally stepping on their mound they will swarm. They simply think they are being attacked, and they swarm in self defense.

Answer by  bl834 (1317)

Mostly because something has disturbed their nest. They are very aggressive and do not distinguish between disturbances before swarming/attacking (such as sprinklers or an animal).