It looks like this is going to be one of "those" years. The large populations of boxelder bug nymphs noticed last summer have matured into the familiar adults and have begun to migrate to the sunny south side of houses and buildings. It could be a long fall based on the number of calls and messages received so far.
During the summer BEBs live, feed and reproduce on trees, shrubs and other plants (including boxelders, maples, ashes and others). They feed on sap from their host plants but do not cause significant damage. In late summer the immatures transform to winged adults that migrate to sheltered, protected locations where they can survive the winter.
BEB adults always go into migration-mode during September and October as temperatures and day-lengths decrease. The bugs are most numerous and most annoying on the really warm, nice days in the fall when you want to be outside.
There is no magic control, and certainly nothing that will eliminate boxelder bugs. The best deterrence is to prevent entry into the house by caulking and sealing possible entry sites (cracks and gaps).
Spraying masses of boxelder bugs on the side of your house with a lawn and garden insecticide (such as bifenthrin or permethrin) or soapy water spray will kill the ones you directly hit. But the sprays have little or no residual activity and will not affect the ones that come the next day (or the next hour!). Frequent reapplication will be required to make a dent in the population, as more bugs keep arriving as long as the sun keeps shining! One reference stated BEBs may fly as for as two miles while randomly searching for places to land.
Since frequent reapplication will be needed, it makes more sense to use the least-toxic alternative available. That would be insecticidal soap or a soapy water spray made with 1 tablespoon of liquid detergent per quart of water. Spray early and spray often, as often as you have time to do it.
Boxelder bugs that find their way inside should be swept up and discarded. Sprays are even less effective indoors.
See our Clinic article on boxelder bugs for more information.