Melee Weapon Attack: +7 to hit, reach 0 ft., one creature in the swarm's space. Hit: 12 (2d6 + 5) piercing damage, or 6 (1d6 + 3) piercing damage if the swarm has half of its hit points or fewer. The target must make a DC 15 Constitution saving throw. On a failed save, it takes 21 (6d6) poison damage and is poisoned until the end of its next turn. On a successful saving throw, it takes half as much poison damage and is not poisoned.