Bites

Melee Weapon Attack: +5 to hit, reach 0 ft., one creature in the swarm's space. Hit: 14 (4d6) piercing damage, or 7 (2d6) piercing damage if the swarm has half of its hit points or fewer. The target must make a DC 13 Constitution saving throw, taking 7 (2d6) poison damage on a failed save, or half as much damage on a successful one. If the target is wearing nonmagical armor, the armor takes a permanent and cumulative -1 penalty to the AC it offers. Armor reduced to an AC of 10 is destroyed.

Infest Corpse (Recharges after a Long Rest)

The plaresh targets one dead humanoid in its space. The body is destroyed, and a new plaresh rises from the corpse. The newly created plaresh is free-willed but usually joins its creator.