How do they get into the house, its as if they are beamed in, there are no gaps in the floor as its concrete and no big gap to get through, are they aliens, help?
They usually get in under the door, remember they are soft and slimy so they can slime their way through very small gaps, also try any air vents that come into the rooms eapecially if you have a damp area, like an old cupboard under the stairs old damp kitchen cupboards etc.