The Brown Marmorated Stink Bug (Halyomorpha halys) is a common invasive pest, widely recognized for its shield-like body shape and tendency to invade human dwellings. Originally from East Asia, this insect has spread across the United States, becoming both an agricultural threat and a significant household nuisance. Understanding their movements is key to managing them, as their daily and seasonal rhythms dictate when they interact with people. The answer to where they go at night depends entirely on the season and their biological drive at that time.
Daytime Basking and Nocturnal Movement
The daily rhythm of the Brown Marmorated Stink Bug is governed largely by temperature and light, as they are cold-blooded insects. During the active spring and summer months, adults often bask in sunlight on host plants, which aids in thermoregulation and provides the necessary energy for their daily activities. The daytime period is primarily spent feeding on the juices of fruits, vegetables, and ornamental plants, using their piercing-sucking mouthparts.
As the sun sets, their behavior shifts from feeding and basking to movement and dispersal. Stink bugs are strong fliers and often exhibit crepuscular or nocturnal activity, particularly when moving between feeding sites. Many species display a positive phototaxis, meaning they are attracted to light sources after dark. This attraction is why they are often seen congregating around porch lights, windows, and other illuminated areas in the evening hours. Their mobility allows them to readily fly between urban, agricultural, and forested areas in search of new resources.
Overnight Resting Locations in Nature
During their active season, from spring through early fall, stink bugs seek temporary, protected locations for overnight rest. When outdoors, these short-term hiding spots offer shelter from predators and the elements. They commonly retreat to dense, shaded areas within their host plants to rest between periods of feeding.
Typical natural overnight locations include finding refuge under leaves or dense foliage in trees and shrubs. They may also tuck themselves into crevices in the bark of trees, under loose stones, or within accumulated ground debris and weeds. These spots provide a dry, dark, and tight space where they can remain relatively still until the following day. This behavior represents a standard nightly pause in activity rather than a long-term survival strategy.
The Seasonal Drive to Enter Structures
The most significant and noticeable movement of stink bugs occurs seasonally as they prepare for the winter months. This is not a nightly rest but a long-term migration driven by the need to enter a state of dormancy, known as diapause. In late summer and early fall, typically starting in September and October, dropping temperatures and decreasing daylight hours trigger the adult bugs to seek protected overwintering sites.
Stink bugs prefer dry, cool, and protected voids for diapause, and man-made structures provide an ideal substitute for natural shelters like dead standing trees or rocky outcroppings. They are drawn to the sunny, warm sides of buildings, often the south and west-facing walls, where they aggregate in large numbers before entering.
The bugs enter structures through tiny cracks, gaps around window and door frames, utility penetrations, and unscreened vents. Once inside, they move into secluded areas like attics, wall voids, chimney flues, and crawl spaces, where they remain inactive throughout the cold months. Warm spells during the winter can prematurely rouse them, causing them to mistakenly emerge into the living space of the home. This seasonal, survival-based movement into houses is the primary reason homeowners encounter Brown Marmorated Stink Bugs indoors.