I had that same problem in my last apt. Ants would be everywhere..

I went out and bought boric acid...i laid it all around the lining of my walls and all ants disappeared...

What it does is when ants go out scouting and they find something...they usually tend to leave a scent trail...what the boric acid does is kills the scent trail and also kills the ants in the process....i poured that stuff around my baseboards where i noticed the ants coming from and voila....no mo ants in my pants