The Brown Marmorated Stink Bug (BMSB), Halyomorpha halys, is an insect species originally from Asia that has become well-established across much of North America. These shield-shaped insects are known primarily as significant agricultural pests that damage numerous crops, and for their tendency to become a nuisance inside homes. As autumn temperatures drop, homeowners frequently encounter these adults, prompting the question of how they survive the harsh winter months. The answer is not simple hibernation but a physiological process that allows them to endure the cold and re-emerge the following spring.
How Stink Bugs Survive the Cold
Stink bugs do not truly hibernate like mammals; instead, they enter a state of dormancy known as diapause. This is a pre-programmed physiological arrest triggered primarily by the decreasing length of daylight in late summer and early autumn, along with cooler temperatures. During diapause, the insect’s metabolism slows dramatically, allowing them to conserve the energy reserves they built up from feeding during the warmer months.
This dormant state involves a cessation of both feeding and reproductive development. Female stink bugs halt the development of eggs in their ovaries until conditions become favorable again in the spring. Entering diapause is a prerequisite for the insects to achieve their maximum level of cold tolerance.
Diapause helps the insects survive by promoting changes in their body chemistry that increase their tolerance to low temperatures. They are chill-intolerant, meaning they cannot survive extended exposure to temperatures that cause freezing within their tissues. Diapause allows them to depress their supercooling point—the temperature at which their body fluids freeze—which helps them survive in buffered microclimates even when outdoor air temperatures fall below freezing.
Where Stink Bugs Seek Shelter
The search for suitable overwintering sites begins in the fall, driven by the same environmental cues that induce diapause. To ensure survival, the insects must find a dry, protected location that shields them from the most extreme fluctuations in weather and moisture. Stink bugs accomplish this by aggregating, or gathering, often using pheromones to signal and attract others to a successful overwintering site.
For homeowners, this aggregation behavior is why the bugs often appear on the sunny, warm sides of houses before moving inside. Human-made structures like homes, sheds, barns, and garages provide the ideal environment. They offer a dry, temperature-buffered space that mimics the large, standing dead trees they might use in a natural setting. The bugs do not damage the structure itself, but they exploit any opening to gain entry.
They squeeze through tiny cracks and crevices, seeking refuge within the structure. Common hiding spots include wall voids, attics, false ceilings, and spaces underneath siding. They also enter through unsealed vents, utility cutouts, and gaps around window and door frames. Inside these secluded spots, they remain largely inactive throughout the winter, waiting for the return of warmth and longer days.
Spring Awakening and Departure
The end of the winter dormancy period is signaled by rising ambient temperatures and increasing photoperiod, or longer daylight hours. As the internal temperatures within the wall voids and attics begin to warm up, the stink bugs are prompted to end their diapause and resume activity. This transition typically occurs in early to mid-spring.
Once active, the bugs instinctively seek to exit the structure to return to the outdoors, where they can find host plants for feeding and begin the reproductive cycle. This is why homeowners often notice the sudden appearance of clumsy, buzzing stink bugs inside their living spaces, particularly around windows and doors. The insects are not emerging from the outdoors; rather, they are attempting to move from their interior hiding spots toward the light, seeking the way out.
The adults that successfully emerge from their overwintering sites will immediately begin feeding and mating to start the next generation. These overwintered adults are responsible for laying the first clutch of eggs, initiating the annual cycle of population growth. The appearance of the bugs inside the home is a temporary, transitional phase as they attempt to locate an exit to the outdoor environment.