That sucks, right after Thanksgiving we had a problem with them in out=r house and we could not figure out where they came from. We have a 6 year old that likes to stash food around but we searched hogh and low and sanitized everything, and I do mean everything! Under couches, beds, in between the mattresses, under and in every cab, fridge, etc! Never did find where they came from as it was very cold outside during those few weeks before and after. We just went around like mad people and killed and sprayed for a week before the problem just disappeared!