The Brown Marmorated Stink Bug (BMSB) is an invasive insect originally from Asia that has become a widespread nuisance pest across the United States. These shield-shaped insects, recognizable by their mottled brown coloring and lighter bands on the antennae, do not bite people or cause structural damage, but they invade homes in large numbers. The presence of these bugs is a seasonal phenomenon tied to their instinctual need to find a secure, protected place to survive the colder months. Their search for shelter transforms them from an outdoor pest into an indoor problem, often catching homeowners off guard in the early fall.
Understanding Seasonal Migration
The sudden appearance of these insects is governed by a predictable annual cycle driven by temperature and day length. Throughout the spring and summer, the bugs feed on a variety of plants, including fruits, vegetables, and ornamental trees, developing through several nymphal stages outdoors. As day length shortens and temperatures begin to drop in late summer and early fall, adult bugs enter a resting state called diapause and begin seeking shelter to overwinter. This migration, typically spanning September and October, marks the transition from outdoor feeding grounds to hibernation structures. The bugs seek a cool, dry, and protected location where they remain dormant until they emerge in the spring, usually between March and April, to fly outside and begin their reproductive cycle.
Common Outdoor Hiding Spots
Before they penetrate the interior of a home, the insects congregate in specific outdoor locations to prepare for the winter. In natural settings, they prefer to overwinter in dry crevices, such as under the thick, peeling bark of dead, standing trees, particularly oak and locust varieties. They are less commonly found in moist environments like leaf litter or mulch, preferring elevated and dry refuge. When structures are nearby, the bugs are strongly attracted to the sunniest sides of buildings, often the south or west-facing walls, where they bask in the afternoon warmth during the fall migration. They will gather near common entry points, including around window and door frames, utility penetrations, and under fascia boards and loose siding.
Identifying Interior Overwintering Locations
Once inside a structure, the bugs seek out inaccessible, undisturbed locations where they can remain dormant throughout the winter. Their preference for narrow, protected spaces leads them deep into the building envelope, often utilizing wall voids, attics, and crawlspaces as primary hibernation sites. Unheated attics are frequently noted as the most favored overwintering location within a building, while basements and crawlspaces are less commonly used. The bugs gain entry through remarkably small gaps, such as cracks around window and door trim, unscreened roof and gable vents, and openings where utility lines enter the home. A sudden temperature increase—perhaps from a home’s heating system—can draw them out into the living space, where they are often seen emerging from cracks behind baseboards, around ceiling light fixtures, and through exhaust fan openings.