Traits

Keen Smell: The swarm has advantage on Wisdom (Perception) checks that rely on smell.

Swarm: The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny rat. The swarm can't regain Hit Points or gain Temporary Hit Points.

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.