Swarm of Insects

If the swarm has a Climb Speed, the swarm can climb difficult surfaces, including along ceilings, without needing to make an ability check.

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.

or 3 (1d4 + 1) Poison damage if the swarm is Bloodied.

Climb or Fly 20 ft. (DM’s choice)