Spider Climb. The swarm can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

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.

Bite. Melee Weapon Attack: +6 to hit, reach 0 ft., one target in the swarm's space. Hit: 10 (4d4) piercing damage, or 5 (2d4) piercing damage if the swarm has half of its hit points or fewer.

The creature must succeed a DC 18 Constitution saving throw or be poisoned for 1 minute. At the beginning of the poisoned creatures turn it gains an additional +1 to its AC, and an additional +2 to its Strength score (to a maximum of 30). The poisoned creature must then use all of its actions, bonus actions, and movement to attack the closest creature within 30 feet that's not the swarm. If there are no other creatures, the poisoned creature may attack the swarm. At the end of the creatures turn, it may make another Constitution saving throw against the poison.

After 1 minute, the creature loses all benefits gained by the poison.