B5
Queller demons were an extraterrestrial demon species that, oddly enough, dwelled within certain meteors. They were summoned to eliminate the insane, particularly in middle ages Europe.
Ben summoned one to Sunnydale in 2000 to deal with the large number of mental patients Glory was creating, though it was killed by Buffy Summers when it targeted her mother.
Powers and abilities
Queller demons were able to stick on flat surfaces such as walls and ceilings. Having slug-like bodies they usually crawled but were also capable of leaping with great agility. They had the ability to track down the insane and to spit a gooey, alkaloid substance which they used to choke their victims. Given their usual habitat, they could most likely survive in the vacuum of space unaided.