Bites (swarm has more than half HP)[/B][/I]. Melee Weapon Attack: +4 to hit, reach 0 ft., one creature in the swarm's space. Hit: (2d4) piercing damage.
Bites (swarm has half HP or less).[/B][/I] Melee Weapon Attack: +4 to hit, reach 0 ft., one creature in the swarm's space. Hit: (1d4) piercing damage.
It seems to me that a swarm should at least have something akin to pack tactics, i.e. advantage on their attacks (because of the sheer number, the odds must be ever in their favor?!) and I would even hazard that they should have multi-attack (at least while above 50% HP).