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 beast.
Bites. Melee Weapon Attack: your spell attack modifier to hit, reach 0 ft., one target in the swarm’s space. Hit: 2d6 + 1 piercing damage.