Swarm of Rats is a Medium swarm of Tiny beasts with unaligned alignment and Challenge Rating 1/4 in the 2014 SRD. This stat block includes AC 10, 24 hit points, speeds, traits, and actions.
Bites - Melee Weapon Attack: +2 to hit, reach 0 ft., one target in the swarm's space. Hit: 7 (2d6) piercing damage, or 3 (1d6) piercing damage if the swarm has half of its hit points or fewer.