Diseased Bites

Melee Weapon Attack: +7 to hit, reach 0 ft., one creature in the swarm's space. Hit: 10 (4d4) piercing damage plus 21 (6d6) necrotic damage, or 5 (2d4) piercing damage and 10 (3d6) necrotic damage if the swarm has half of its hp or fewer. The target must make a DC 15 Constitution saving throw or contract a disease (see the Bog Rot trait).