swarm in(to) (something or some place)
To move in(to some place or thing) very quickly and in great numbers. Customers swarmed in the moment we opened our doors for our huge Black Friday sale. Bugs began swarming into the house through the open window. Police swarmed in the building to apprehend the suspect.
swarm in(to something)
[for a throng] to crowd into something or some place. People were swarming into the auditorium to hear the guitarist. They swarmed in and ran for the best seats.