Stink bugs, particularly the Brown Marmorated Stink Bug (BMSB), are frequently seen near homes, leading many people to wonder if they are nocturnal. These insects are not strictly nocturnal; their natural activity patterns are primarily diurnal (active during the day) or crepuscular (active during twilight hours). The perception of them being nighttime pests is largely due to their powerful attraction to artificial light and a seasonal search for warm shelter.
Daily Activity and Feeding Cycles
In their natural environment, stink bugs are generally insects of the daylight hours, with their activity dictated by temperature and the need to feed. The primary life cycle of the adult stink bug revolves around consuming plant matter. This need for warmth to fuel their movement means they are most active during the warmest parts of the day, when solar radiation is highest.
Feeding activity often peaks during mid-day and extends into the late afternoon. Some species, like the Southern Green Stink Bug, show higher feeding rates during the scotophase, or the dark period. The timing of their activity is a biological strategy to maximize feeding and mating opportunities when environmental temperatures are most favorable.
The movement and feeding of these insects are closely tied to their circadian rhythm and environmental cues such as light and temperature. Unlike truly nocturnal insects that rely on darkness for their major activities, stink bugs use the light and warmth of the day to locate food sources and mates.
Attraction to Artificial Light Sources
While stink bugs are not naturally nocturnal, their presence around porch lights and windows at night is a result of a strong behavioral response called positive phototaxis. This is the innate tendency of an organism to move toward a light source. Researchers have determined that adult BMSBs are most attracted to white light and the shorter wavelengths, specifically the UV and blue-green spectrums (368–455 nm).
This attraction to light is why they appear to be active at night, as they are drawn to human-made light sources from a distance. Porch lights, street lamps, and even light filtering from interior windows can pull them away from their natural habitats in fields and trees. Studies have identified an optimal light intensity for attraction in adults to be around 75 lux, which is comparable to the brightness of a typical residential outdoor light.
This positive phototaxis is a significant factor in why they become a nuisance pest, aggregating on the exterior walls of homes after sunset. This nocturnal presence is therefore a side effect of human development and lighting, not their primary behavioral pattern.
Seasonal Changes and Overwintering Behavior
The other major factor contributing to human encounters with stink bugs is their seasonal migration, which is entirely separate from their daily activity cycle. As temperatures drop in late summer and early fall, stink bugs begin to seek suitable locations for overwintering. This process is triggered by changes in photoperiod (day length) and decreasing temperatures.
The insects enter a state of metabolic reduction known as diapause, where they cease feeding and reproduction to survive the cold season. To achieve this, adult stink bugs aggregate in large numbers and seek warm, protected microclimates. Human-made structures, such as houses, sheds, and garages, provide the ideal, buffered environment for this period of dormancy.
The bugs gain entry through small cracks, vents, and openings, often congregating in attics, wall voids, and behind baseboards, where they remain sluggish and inactive. Their appearance inside homes during the fall and winter is not a sign of feeding or breeding activity, but simply a consequence of their need for a warm, dry place to wait out the cold until spring arrives.