Box Elder bugs are plant feeders, so why would they be attracted to a home? The four main components that play into this bug’s decision include proximity to populations, warmth, aggregate overwintering behavior, and luck (or lack thereof).
The closer your home is to a Box Elder bug host plant, the more likely you are to encounter these bugs. The most common host for Box Elder bugs is the female box elder tree, so if you have one of these sitting in your backyard, you may have the associated bugs crawling around your home all throughout the spring and summer months.
As temperatures drop in the late summer and fall, the Box Elder Bug will seek out places to maintain their body temperature. Since the sun is strongest on the south and west walls, these will be the warmest places and will be most attractive to bugs seeking warmth. In some cases, the type of building material or even color of the exterior of the home can play into making one home more attractive than another. Other heat producers such as dryer vents or heating systems may draw the bugs
father inward especially as temperatures fall even more in later fall and winter.
Aggregate Overwintering Behavior
Box Elder bugs do not have a food source in the winter in most places, so their biological programming sends them into a hunt for a place to go dormant for the winter and wait for a food source to pop back up in the spring. As they search for cracks, crevices, and voids that they can use as refuge from the elements, they will also tend to gravitate toward other Box Elder bugs that have already landed on a home. Their aggregation allows them to huddle tougher in the colder nights and rely
on each other for protection.
Sometimes one home will be just as close to a Box Elder population as the next one but will have far more bugs than its counterpart. If none of the above explanations provide adequate reasoning for them choosing a particular home, it can be entirely based on chance. Perhaps the breeze on the day they decided to seek an overwinter site was blowing toward that particular home. Maybe the first one just felt like flying left instead of right. Maybe the predator that was chasing the bugs at that time decided to attack in that direction. Whatever the case may be, there are always some homes that seem like they should be less attractive to the Box Elder bug than the next home but end up with more than their fair share.