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.
Bites. Melee Weapon Attack: +2 to hit, reach 0 ft., one target in the swarm's space. Hit: 7 (2d6) 2d6 piercing damage, or 3 (1d6) 1d6 piercing damage if the swarm has half of its hit points or fewer.
Environments. Marshes, Swamps, Urban