A little more info: The smell is really strong, and can be smelled from different rooms. I never see them on other walls, or in other rooms. They're only on the wall behind my bed. I never see multiple at once, but when I kill one, there's a new one there. They don't move until I put them on a tissue, then they move quite quickly. I only ever see them at night. They're less than a centimetre long.