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 insect. The swarm can't regain hit points or gain temporary hit points. Sacrificial. On a successful hit with its sting attack, the swarm of bees loses hit points equal to the damage dealt.
Sting. Melee Weapon Attack: +3 to hit, reach 0 ft., one target in the swarm's space. Hit: (2d4) poison damage, or (1d4) poison damage if the swarm has half of its hit points or fewer. On a hit the target must succeed on a Constitution saving throw DC 13 or be frightened (condition) of the bees for 1 minute.