The pest control textbook says, "cut down the tree!" I don't subscribe to this solution, but if the tree is yours, you should begin there. If you treat the sick tree - you may need a tree service to do this - you may be able to get rid of the problem completely. It could take two treatments. If there are many trees and the neighbors also have them, then you won't make much progress. If you can't afford a tree sprayer, use a good pesticide on the trunk and the surrounding ground in the early spring before they emerge. I recommend Home Defense. It has a 6 month residual, it's not very toxic, no odor, its very repellent to bugs, and you can buy it at home dippy.
This bug likes boxelders (duh) and silver maples. Here in CO they have also taken to scrub oak. They lay eggs at the base of the tree or on the trunk in the spring when the seed pods emerge. In good conditions there will be two generations by the fall when the adults start looking for warm hibernation spots. They emerge on sunny winter days and migrate to warm surfaces - like the south side of your house.
Your best defense is caulking and sealing. If your house has lap siding, it'll be a lot of work. Be certain to close the gap made by the siding overlapping the foundation. Good screen fit and tight doors are necessary. This will also reduce your heating bill.
Once the bug shows up inside, you can bet the space between the inside and outside walls is loaded. Wait to do your caulking until early summer so they are not trapped in the walls.
You can also spray the sunny sides of the structure in the late fall with the chemical above. The bugs will land and then quickly leave before they look for entry points. It doesn't really kill them because the contact time is too little.
Not all boxelders attract bugs. We lived where there were 4 large trees near the house. In the fall the bugs would pile up around the foundation by bushels. We moved to a place that had 2 large boxelders close to the house and they never attracted bugs. They were both male trees. The female trees draw the bugs.
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