Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny insect. The swarm can't regain hit points or gain temporary hit points. Spider Climb. The swarm can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check. Web Sense. While in contact with a web, the swarm knows the exact location of any other creature in contact with the same web. Web Walker. The swarm ignores movement restrictions caused by webbing.
Bites (swarm has more than half HP). Melee Weapon Attack: +3 to hit, reach 0 ft., one target in the swarm's space. Hit: (4d4) piercing damage plus (2d6) poison damage. The target must make a DC 11 Constitution saving throw, taking the poison damage on a failed save, or half as much damage on a successful one. If the poison damage reduces the target to 0 hit points, the target is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way. Bites (swarm has half HP or less). Melee Weapon Attack: +3 to hit, reach 0 ft., one target in the swarm's space. Hit: (2d4) piercing damage plus (1d6) poison damage. The target must make a DC 11 Constitution saving throw, taking the poison damage on a failed save, or half as much damage on a successful one. If the poison damage reduces the target to 0 hit points, the target is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way.