These are trees that feed on living organisms.
The trees are thought to be the Snakes of Alvar Pena in the Adventures of Ugo.
The trees "roots" only reach to the tip.
The trees stop moving in cold winds.
These trees die, which Sonju make a tunnel by connecting the Bloodsucker Trees underground forming a maze that he says only him and Mujika can find the exit. But later Mujika says she would be lost. 
- ↑ Yakusoku no Neverland Manga: Chapter 48, Page 13