USU Extension has a Fact Sheet about Boxelder bugs. You can find it at this link: http://extension.usu.edu/files/publications/factsheet/boxelder-bugs06.pdf

These bugs are very difficult to control. Fortunately, they don't harm people, homes, or plants. But they can be a terrible nuisance.

One suggested control is to drown them. Line up some plastic trays underneath the wall where the bugs are congregating, then spray water down the wall so that the bugs are washed down into the trays of water. Because they don't swim well, most of them will be trapped and drowned.

To keep them out of your home, seal all cracks and crevices. You can use sticky traps in windowsills to help catch some.  

Boxelder Bug Management.

Please read over our fact sheet for more information . In general, they are very difficult (if not impossible) to eradicate. Boxelder bugs are considered nuisance pests, but sometimes they can damage fruit. Mostly they accidentally move into homes for warmth during the winter and that’s when they really become a bother.