Until the Fairy Queen has completed her reincarnation, the dryads had to remain behind. Since they couldn't move freely, they can only manage to maintain rather thin bodies, and barely move.
They tend to shape themselves like female while the Treants shape themselves like a male. In Founding, the Demon Capital Arc, the Dryads and Treants reunited with their master Ramiris and lived on a special floor inside the Labyrinth alongside the elves. After that, they helped their master continue in her research.