Dryad

Lice, or "Dryads" - as coined by the Twelfth Doctor, were insect-like creatures which lived in wood and fed on humans. They lived in a house owned by the Landlord after he found three individuals outside, which had some healing properties that saved Eliza, however turning her partially into wood. In order to properly heal someone however, they had to be regularly fed people, so the Landlord decided to make the house cheap to lure people into buying it. He'd also use a tuning fork to call them to the area where the inhabitants were.

In the end, Eliza controlled all the Dryads into eating her and her son in order to stop the killing that was keeping her alive, and as a result all the Dryads left. (TV: Knock Knock)

Biology
Dryads bore a great resemblance to cockroaches. They had a chitinous hide, were a little bigger and had a brownish red color. They also had biolumenescent antennae on their heads.

Given that the Landlord only found three to start with, only for them to become a gigantic swarm that infested the whole house, it is possible they reproduce asexually and at an incredible rate.

They were extremely sensitive to high-pitched sounds and vibrations. This is how each Dryad communicated with each other. They could be controlled and tamed using music or a tuning fork, as demonstrated by the Landlord.

Diet
The Dryads were carnivorous and fed on prey, mostly humans, who they ensnared with the wood they inhabited. They would then swarm over the target and devour them in seconds.

Behaviour
The Dryads were intelligent insectoids and could sense when people were sick, such as Eliza. They would also cleverly ambush their prey unexpectedly and devour them. They could however be tamed and kept docile with high-pitched sounds like a tuning fork. Eliza also managed to control them mentally due to her mutation.

Abilities
The Dryads had incredible healing abilities and could preserve a person indefinitely by transmuting their body into a substance with the same color and texture as wood. They would however have to be fed in order to maintain this preserved state or the person would revert to their original state and die.

The Dryads' natural habitat was the element of wood which an entire swarm could inhabit. They could also exert fine control over the wood they inhabited and animate it at a molecular level. They could effortlessly emerge or dive into the wood and animate any wooden object such as doors, shutters and trees. They would typically use it to ensnare their prey and then cause the wood to immobilize them or seemingly absorb them.

They attacked their prey by swarming all over their body before breaking them down at a cellular level, effectively disintegrating the quarry. They could however just as easily reconstitute the body of a person they had disintegrated, fully restoring them to life. This was perhaps an extension of their healing abilities.