D is for... Dryads

Giant insects with an affinity for wood, they infested an old house which Bill Potts and her student friends rented. Many years before, a boy living at the property had found a handful of them in the garden and taken them to show his dying mother. The creatures were able to keep her alive, but only by turning her into wood herself. The boy grew up and rented out the house every 20 years or so, usually to young people. The Dryads would attack them and absorb them into the house. Now an old man, the landlord could control the creatures using sound waves. His mother - Eliza - also had control over them. One by one Bill's friends were attacked and absorbed by the Dryads. She and the Doctor met Eliza and convinced her that what her son was doing was wrong, and that she led no real existence at all, hidden away in a tower room in the house. She decided that it was time to bring things to an end, and the Dryads consumed her and her son. The house began to collapse, releasing all of Bill's friends as they had not been fully absorbed into the structure.
The Doctor was unsure if the Dryads, which he named after the mythic wood sprites, were terrestrial in origin or if they had come from another world.

Appearances: Knock Knock (2017).