Ants

We have ants in our kitchen. One day they were all over the floor and noone knew where they came from. All doors closed, no openings or nothing. Very strange indeed. My housemate used the vacuum cleaner to clean the floor up and since then, the landlord has been here and put a white powder in strategic places. I assume this is some kind of ant-poison (or at least poison) although it looks suspiciously much like flour. I don't think its a good idea to taste it so I am going to just leave it there.