On warm fall and winter days, boxelder bugs can become a nuisance by crawling on the exterior of buildings and entering buildings through cracks, crevices and screen doors. This bug grows to about one-half inch long and is black with red lines on its body and wings. Boxelder bugs mainly feed on winged seeds found on boxelder trees.
Controlling boxelder bugs can be simple. Screening or sealing cracks or entrances and vacuuming bugs inside the home helps reduce their numbers. Household spray pesticides are also effective when sprayed directly onto the boxelder bugs.
The most permanent solution to boxelder bugs is removing female boxelder trees, but that may not be practical. Using a residual insecticide such aspermethrin, cyfluthrin, or bifenthrin along the foundation of buildings can reduce boxelder bug invasions. An alternative to commercial insecticides is laundry detergent mixed with water and sprayed directly on the bugs. Be careful to avoid contact with plants because some are sensitive to detergent spray.
For more information, see the following Colorado State University Extension fact sheet(s).