Weevils were so named by Torchwood because they have no means of communicating with them and finding out more about them. They keep one of them captive for study. Jack named it Janet because ‘Barbara just didn’t work’ – a comment he never explained.

Weevils are thought to be extraterrestrial in origin, but a population of a few hundred live in the sewers of Cardiff, having travelled through the rift. They usually live off sewage, but occasionally one will go rogue, come to the surface and attack humans using their sharp fangs. They all seem to wear Torchwood embroidered boiler suits. They have little or no language, but possibly communicate telepathically. While they attack to kill, it is unclear whether this is simply due to a desire for food. They have some family/group behaviour, accompanied by a territorial aggression. They are adapted to survive in dark, damp conditions, and possess great strength and speed. They are also "time sensitive", physically pained by dramatic disruptions in the spacetime rift. They appear to be here to stay as a part of Cardiff’s underworld.

Weevil experiencing suffering of another telepathically in Combat

Tortured Weevil in Combat