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 its hp or fewer. If the target is a creature other than a construct or an undead, it must succeed on a DC 13 Dexterity saving throw or lose 2 (1d4) hp at the start of each of its turns as leeches attach to it and drain its blood. Any creature can take an action to find and remove the leeches with a successful DC 13 Wisdom (Perception) check. The leeches also detach if the target takes fire damage.