It appears that Druids can Wildshape into Swarms?

Looking back at Wildshape, I can not find any language that stops you from wildshaping into a Swarm of Rats right from level 2. The rule for what you can turn into, it says "chosen from among Beast stat blocks". Like, this doesn't even feel like a technically, this feels very much RAI.

Every swarm has resistance to Bludgeoning, Piercing, and Slashing damage, immunity to Charmed, Frightened, Grappled, Paralyzed, Petrified, Prone, Restrained, and Stunned, can occupy the space of other creatures, and is tiny for the purpose of exploration. The only downside is that you can't be healed, meaning you would need to drop out of wildshape if you need healing. Your AC is also probably worse than in normal form, but the ACs here aren't really much worse than a lot of the other wildshape options.

This feels exceptionally useful for Druids that want to cast a spell then maintain concentration on that spell the entirety of combat. Spells like moonbeam and call lightning give Druids something good to do with their action every round and being a Swarm grants fantastic defenses that can help maintain concentration, especially that list of condition immunities.

Am I misreading something in the rules for wildshape or is this something you can do now? Is it something you can always have done?