Understanding the biology of the Brown Marmorated Stink Bug (BMSB) largely answers why they land on people. This invasive species, originally from Asia, is the primary culprit for this behavior across North America and parts of Europe. The phenomenon is not a personal attack, but an accidental, close-range misjudgment driven by powerful environmental cues. Their instinctual search for shelter, combined with a sensory system tuned to heat and light, leads them to mistake large, warm objects—including people—for a safe haven.
Environmental Attractants That Draw Them Close
The journey that ends with a stink bug landing on a person begins with the bug reacting to broad environmental signals. One primary driver is phototaxis, the instinctual movement toward light. Artificial light sources, especially those that emit shorter wavelengths like ultraviolet (UV) and blue light, act as powerful beacons.
Porch lights, exterior floodlights, and interior lights escaping through windows are particularly attractive during the evening hours. This attraction is pronounced in the late summer and early fall as the insects begin their search for shelter.
BMSB also display thermotaxis, a drive toward heat. They gravitate toward the sunniest sides of buildings in the late afternoon, absorbing warmth to prepare for the coming cold. These large, warm, vertical structures offer both a visual cue for a safe location and a source of stored thermal energy.
The bugs are drawn to the general vicinity of a human dwelling by these strong signals. This initial attraction sets the stage for accidental, close-range landings on people nearby.
Why Your Body is a Target for Landing
Once a stink bug is in close proximity, your body becomes a target because its sensory profile mimics a desirable overwintering site. The human body is a large, warm object that continuously emits heat, which the insect’s thermoreceptors can detect. They perceive this radiating warmth as a potential sheltered spot, similar to the crevices they are instinctively seeking.
The bugs are not seeking to bite or feed on you; they are simply attempting to land on what they perceive as a stable, warm structure. This mistaken identity is reinforced by trace chemical cues that your body emits. Exhaled breath and skin emit small amounts of carbon dioxide and moisture, which can signal the presence of a large, metabolically active mass.
A third factor is the role of aggregation pheromones. Stink bugs release these chemical signals to call other members of their species to a newly discovered safe location for overwintering. If a person is near a spot where a bug has deposited a pheromone, they may be perceived as part of the safe, established cluster, leading to an accidental landing.
The Driving Force of Seasonal Behavior
The reason these landings become a widespread problem is rooted in the stink bug’s annual survival strategy known as diapause. This is a state of dormancy, similar to hibernation, that the adult bugs must enter to survive the cold winter months. The intense drive to find shelter begins in the late summer and accelerates through the fall, typically starting around September.
During this period, the survival instinct overrides caution, leading to a massive, concentrated movement toward vertical structures. The bugs are desperate to find a secluded, dry, and protected space, such as voids within walls, attics, or under siding. This migration makes them numerous and visible.
The behavior subsides once they have successfully found a sheltered crevice or once ambient temperatures drop enough to induce full dormancy. Until that point, their focus on locating any warm, stable structure means a person standing still can easily become an unintended, temporary landing platform.