If the one is BED BUGS, it's quite difficult to clear them. You must use the綠水開水抺 from time to time, may be every day. They usually hiding under the bed or safa, must change the bed sheets often. I have the experience, I think it comes from my maid, because she stayed in the boarding house for a week before came to my house.
After she came, my children started being bited by the bed bugs. It's horrible.....