I notice whenever I leave food uncover, they would just feast on it. Even cup i used to drink soft drink, if I don't get it washed immediately, these NEIGBOURS would just fill inside the cup. My question is? Where do they come from and where are they living

Just fumigate your house, insecticide is a waste of time.

Akin, you dont seem to get the point.

I used to wonder where they come from too but I just concluded that we can't have the answer to every question. Maybe the food particles breed the ants.

I used to have the same problem despite use of all types of insecticides. At a point my sister saw it as a spiritual attack, until the fumigator was called in to do his thing. Now, not even one can be seen no matter how long I leave dirty plates in the sink.
     Talking of where they come from? The sand of course, in small cracks even under concrete. They gather so quickly, cos of their cooperative nature.