Blood Worm

You infect a creature you can see within range with a magical disease in the form of a malignant parasite. Once per turn when a creature hits the infected target with a weapon attack, that attack deals an additional 4d6 necrotic damage, and the attacker regains hit points equal to the necrotic damage dealt. Each time the infected target takes this necrotic damage, it makes a Constitution saving throw against the spell. If the saving throw succeeds, the spell ends.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the necrotic damage increases by 1d6 for each slot level above 4th.