Swamp Rats

In the Nightshade Chronicles series book two, The White Assassin, Billycan is deep in the southern swamps. He rules a primitive horde of savage swamp rats eager to overrun Nightshade City and claim it for their king. The bats and snakes who also resided in the swamp thought them crude and brutal, but they are later discovered to have strong and deep emotions. Unbeknownst to the Trillium rats at the start of the book, the swamp rats are actually Trillium rats which migrated away from the city. Eventually, the Trillium rats realise the main difference between them and the swamp rats are how many swamp rats speak in a strange, seemingly stupid way.