Utah State University Extension
Boxelder bugs are a common nuisance insect to many homeowners. Although boxelder bugs are active throughout the summer, many people don’t notice them until they start “sunning” themselves on structures, particularly the southern-facing walls. As temperatures start to decrease in the late summer and fall, large numbers of adults will move from plants and congregate on heated buildings.
Hodgson, Erin W. and Roe, Alan H., "Boxelder Bug" (2010). All Current Publications. Paper 864.