Bites - Swarm of Poisonous Snakes

Monster Manual - 5e, D&D Basic Rules

Bites. Melee Weapon Attack: +6 to hit, reach 0 ft., one creature in the swarm's space. Hit: 7 ( 2d6 ) piercing damage, or 3 ( 1d6 ) piercing damage if the swarm has half of its hit points or fewer. The target must make a DC 10 Constitution saving throw, taking 14 ( 4d4 ) poison damage on a failed save, or half as much damage on a successful one.