Swarm of Aracha (5e Creature)
From D&D Wiki
Swarm of Aracha
Large swarm of Small beasts, unaligned
Saving Throws Dex +4, Wis +3
Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Small beast. The swarm can't regain hit points or gain temporary hit points. Other creatures treat the space this swarm occupies as difficult terrain.
Swarm Tactics. The swarm has advantage on an attack roll against a creature if it is within 5 feet of that creature.
Sand Burrowing. While on soft ground such as sand, the swarm gains a burrowing speed of 10 ft.
Spider Climb. The swarm can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.
Bite. Melee Weapon Attack: +2 to hit, reach 5 ft., one target. Hit: 2 (1d4) piercing damage, and one aracha "clings" and becomes physically attached to the target, and the aracha's speed becomes 0 feet while clung; it occupies the target's space and moves with it. While the aracha is clung to the target, the target's attack rolls have disadvantage against the aracha. While the aracha is clung to a target, it can make another bite attack against the target without having to roll to hit. The aracha can no longer cling if it is reduced to 0 hit points, or moves away from the target. Any number of clung creatures are removed if the target creature takes an action to remove them.
Swarms of aracha will form deep within desert ruins, normally whenever their mother has been recently creating offspring. Coming together to form a swarm is the best chance at survival these little creatures will get.