Boxelder bugs are classified as “occasional invaders,” (rarely a constant issue, showing up when you least expect them).
Boxelder bugs are ½ inch long and have an elongated, oval shape. They are mostly black with red wing veins and markings on the abdomen. The inside of your home is not an ideal habitat, but since they don’t overwinter well outside, they will hibernate inside wall voids or behind siding. Sometimes your heating system may wake them, causing them to become a major nuisance and their feces can also cause red stains on curtains and furniture, adding to your headache.
When the weather warms up in late April or early May, the adults will leave your home and fly back to their host tree (a seed-bearing Boxelder tree so they can feed on its seeds; but, can also feed on apple, plum or maple trees). During the spring, they are rarely a problem; however in autumn, the adults will congregate on the South side of rocks, trees, and buildings where the sun is warm. Once a large enough number have gathered, they will fly towards a nearby building to hibernate.
If you see a Boxelder bug in your home, your immediate reaction may be to grab the nearest shoe, but don’t. Refrain! The Boxelder bugs emit a very unpleasant smell. The best course of action to take is to grab a vacuum and suck them up. However, killing Boxelder bugs inside your walls can attract the Dermestid Beetles who feed on the decaying bodies of dead Boxelder Bugs. Instead, continue to vacuum vigilantly and wait until June or July, when Boxelder bugs leave your home then take preventive measures outside.
The best thing you can do to reduce Boxelder bug issues is exclusion (eliminating entryways). While it is impossible to close every entryway, you can take measures to greatly reduce your problem. First, screen all vents on the outside of your home with 16-mesh screening. Areas of major concern include; roofs, overhangs, and weep-holes in brick buildings. Next, use a silicone-based caulking and seal around cable entrances, windows, doors, overhangs, fascia boards, etc. (basically any area with a gap that bugs can get through). Not all insects require a chemical treatment; sometimes, a little bit of TLC is enough.