Invasive insects like the Brown Marmorated Stink Bug (BMSB), native to Asia, are agricultural and household pests in North America. Their life cycle includes a phase where they seek shelter inside human-made structures. The frequent presence of this shield-shaped pest inside homes leads many to question its natural daily activity patterns. Understanding the typical rhythm of the stink bug is the first step in managing its presence.
Daily Activity Patterns
Stink bugs are not truly nocturnal insects, meaning they are not primarily active during the night. Their natural rhythm is largely diurnal, with peak activity occurring during the day when temperatures are warmer. They spend daylight hours feeding on plants, mating, and dispersing to new host sites.
A significant portion of their movement is also crepuscular, meaning they are active during the twilight periods of dawn and dusk. This preference for light and warmth allows them to maximize time for foraging and reproduction. During the hottest part of the day, they may seek shade, but their general movement is closely tied to the presence of sunlight and warmer temperatures. Adult stink bugs can fly substantial distances, with an average dispersal of five to six kilometers.
Light and Heat Attraction
The belief that stink bugs come out at night stems from their strong behavioral response to light and heat, which can override their typical daytime cycle. This movement toward light is positive phototaxis, a common insect behavior drawing them to artificial light sources after dark. They are particularly attracted to white light, which is more appealing than colors like green or red.
As evening falls, the glow from porch lamps, security lights, and indoor lights visible through windows acts as a powerful beacon. This attraction causes them to aggregate on exterior walls near these light sources, making their presence noticeable. Furthermore, stink bugs are drawn to the residual heat radiating from buildings after sunset. The warmth stored in the structure, particularly on sun-exposed sides, encourages them to linger and move around during the night.
Overwintering Behavior and Entry
The most common reason homeowners encounter stink bugs active at night relates to their annual preparation for diapause, or hibernation. As temperatures begin to drop in the late summer and early fall, adult BMSB actively seek protected, cool, and dry sites to overwinter. Buildings receiving afternoon sun are ideal substitutes for their natural overwintering sites, which include dead standing trees and sheltered rock crevices. The search for shelter begins in September and October, leading to mass movements toward homes, where they exploit any available entry point.
Common access points include gaps around window and door frames, utility line penetrations, foundation cracks, and unscreened roof or gable vents. Once inside wall voids, attics, or crawl spaces, they enter a dormant state that lasts until spring. However, the warmth of the living space can disrupt this dormancy, causing them to become active even during the night. If the temperature within the structural void or attic rises, the bugs may rouse and emerge into the main living areas through small cracks, electrical outlets, or ceiling fixtures. Therefore, seeing a stink bug crawling across a bedroom wall at midnight is not a sign of a nocturnal insect, but rather an insect accidentally roused from its winter rest by the consistent warmth of the indoor environment.