Vardy

The Vardy (plural: Vardies) were a type of microbot, small robots which collectively controlled the Emojibots that served as an interface for them on Gliese 581 D.

These would gather together to make buildings as well as distribute fertiliser across the colony's wheat. By the time of the Twelfth Doctor's arrival with Bill Potts, the Vardy were a lifeform of their own, a species with sentience and awareness.

When the Emojibots first encountered grief, they considered it an enemy of happiness and thought of destroying it, they called upon the Vardy to kill anyone who wasn't happy, stripping them of skin, organs and muscle leaving behind their skeleton, which later would be used to make calcium-based fertiliser. (TV: Smile)

Behind the scenes
The Vardy were named after Andrew Vardy, a Canadian professor at Memorial University, whose area of research is swarm robots.