Box Elder Bugs feed on the little “whirlybird” seeds that are released from box elder and maple trees in the fall. When colder weather comes, they like to find a nice warm spot to spend the winter. They are only a half inch long, so finding a way into most buildings is not too difficult. Just inside the exterior walls of the building, on the warm sunnier side, is their preference. To stop these pests, exterior cracks and crevices in the building must be sealed. Exterior doors must be sealed tightly on all sides as well.