Boxelder bugs are highly seasonal pests that become most noticeable during the fall and early spring. As temperatures drop, they gather in large numbers on sun-exposed walls, using heat from the structure to stay warm before attempting to move indoors. 

Homeowners often notice clusters forming on exterior siding, windows, and entry points, especially on the sunny side of the home. As they find small cracks or gaps, they may begin to enter wall voids, attics, or window frames to overwinter. Once inside, they typically remain inactive but may reappear on warmer days, leading to repeated sightings over time. This can make it feel like the problem is ongoing, even if no new pests are entering. 

While they do not bite or cause structural damage, their tendency to appear in large numbers and return seasonally makes them a persistent nuisance. They may also leave stains on surfaces if crushed. Preventing entry before seasonal changes is key to avoiding indoor activity.