A single box elder bug may be interesting to look at, even pretty, but when the bugs infest your home, it's hardly fun. Like many bugs, however, box elder bugs are deterred by the smell of vinegar. Use this natural ingredient as a homemade repellent to help staunch the flow of bugs and reduce or eliminate their numbers in your house.
Fill a spray bottle with white vinegar (you can use other vinegars, but white doesn't stain). For best results, use a pump spray bottle rather than a finger atomizer, since this will allow you to spray more and adjust the intensity of the spray.
Spray areas in your home where the bugs like to congregate. Try window sills, near doors or entryways, around the lower edges of walls and inside lighting fixtures.
Give an extra hefty coating of vinegar to places where the bugs seem to be entering your home the most often. Since box elder bugs eat maple leaves almost exclusively, this will often be areas on the side of the house closest to a maple. Bear in mind that it may be in a neighbor's yard.
Go outside and locate the nearest maple trees, if any. Box elder bugs often flock from one of these trees to an indoor area, so if you've got bugs coming in mass quantities, chances are good you've got a maple quite nearby. Spray as much of the straightest path between the tree and an entrance to your home as you can; bear in mind, though, that white vinegar will be harmful to grass if it lands on your lawn.
Make a note of all the locations you've sprayed. Revisit these, especially the most heavily trafficked ones, every couple of days or so and reapply the vinegar.