buy some terro liquid ant killer from amazon for like $4, put a couple dots on a piece of cardboard, and watch them all come and eat it and then they bring it back to the other ants and they all die!! not a solution to the dirty roommates, but it will feel better to not have ants in ur space! i get ants in my room this time every year because of where i live and where my room is in the house (this side of the house gets ants every year regardless of food being left out). works like a charm