Box elder bugs are harmless to people, pets, houses and furniture, but you will definitely want to learn how to get rid of them because they make unpleasant housemates in fall and winter, when swarms sneak indoors for warmth. In addition, box elder bug nymphs can damage tree seedlings and foliage when they hatch in spring.
The best way to kill box elder bugs is to eliminate them before fall temperatures drive them indoors. Remove any female box elder trees near the house, or have a professional apply insecticide to the trees. Since box elder bugs typically return to box elder trees about the time the tree begins to flower, spraying the tree anytime after flowering begins should kill most or all of the insects. A pest elimination specialist can also spray trees with a compound that will prevent box elder bug eggs from hatching. Since box elder bugs will not lay eggs indoors, only the trees need to be treated for eggs.
Once the weather turns cold and box elder bugs come indoors, they are difficult to remove. Before fall comes, prevent box elder bugs from getting in by caulking around door and window frames, around pipes, behind chimneys, and in any cracks in the house's siding. Repair or replace torn or loose screens. A pest control expert can also apply pyrethrin-based insecticide to the south walls of the house to deter box elder bugs. Since pyrethrins degrade in sunlight, however, a weekly application may be required throughout the fall.
To kill box elder bugs inside the house, do not use insecticides. They are inefficient and may put your family or pets at risk of illness. Instead, spray box elder bugs with water containing approximately four percent dish soap by volume. The soap will only work if the bugs are sprayed with it directly. Since box elder bugs are not poisonous to the touch and cannot bite, you can also smash or gather them by hand to dispose of them.