From publisher blurb:
Live for the Swarm.
Druids of the Circle of the Swarm meet in dark and sacred places around the corpses of ritualistically sacrificed beasts. You act for the good of nature, for the good of the circle, for the good of the swarm. Summon fearsome tiny beasts to do your bidding and disperse yourself into the hive mind, your countless forms will blot out the sun.
Have you ever fought an annoying NPC and thought, "Can I shoot hornets at him?" or had a difficult problem that could only be solved by becoming a swarm of rats? If so, this is the book you've been looking for.
This 5 page (2 if we're being honest, not including the cover and copyright pages) handbook includes everything you need to join the Circle of the Swarm as your next druid character.
The swarm shape feature also includes a highly variable stat block with optional features perfect for creating a swarm to fight in your next campaign.
The Circle of the Swarm starts with two base abilities, Summon Swarm and Swarm Shape. These two features form the core of the archetype, giving you the capacity to create swarms to attack your foes and become a swarm of whatever tiny creatures you desire.
Later abilities allow you to enhance your swarms, disperse yourself over a wide area to find hidden secrets, and temporarily disperse to protect yourself or sacrifice parts of your swarm to save an ally.