Vurms

A life-form dwelling in Dwarf mines, originally found in the deep caves in the mountains around Llamedos. Swarming, or slithering, by the hundred, packs of Vurms generate a low but steady luminescence which enables the adapted eyes of Dwarfs to see their way in the deeper mines.

They have other uses as well: Crushed vurms are used to produce 'night chalk', which glows for about a day and is very handy, e.g. for the marking of crime scenes in the dark. And vurm blood is used to create drahts - glowing, unique identity symbols for Deep-Downers - which are made by tattooing vurm blood under the skin.

They are adapted to seldom require feeding, but are carnivorous creatures living on carrion. They are attracted to blood and corpses and will smell dead animals - or dwarfs - from a long distance. They have no teeth so they wait until their food gets runny of its own accord. After a feed, they will shine very much brighter. Almost anything is food to a vurm, who live so deep underground that even a breath is food, blood is food, and anything that was once alive, no matter how mangled it is, is food. Vurms are shown to be so attracted to blood that they would rather die then give up their feast, as shown in Thud!.

Carrot Ironfoundersson is all too aware of this when investigating a murder in the Dwarf community in Ankh-Morpork, during the events in Thud!.