Skeletonize.

If the swarm starts its turn in the same space as a dead creature that is Large or smaller, the corpse is destroyed, leaving behind only equipment and bones (or exoskeleton).

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 scarab. The swarm can't regain hit points or gain temporary hit points.

Actions

Ravenous Bites.

Melee Weapon Attack: +4 to hit, reach 0 ft., one target in the swarm's space. Hit: 14 (4d6) piercing damage, or 7 (2d6) piercing damage if the swarm has half of its hit points or fewer. If the target is a creature, scarabs burrow into its body, and the creature takes 3 (1d6) piercing damage at the start of each of its turns. Any creature can use an action to kill or remove the scarabs with fire or a weapon that deals piercing damage, causing 1 damage of the appropriate type to the target. A creature reduced to 0 hit points by the swarm's piercing damage dies.

Swarm of Scarabs