The brown marmorated stink bug (BMSB), an invasive species from Asia, is a significant nuisance pest for homeowners across North America and Europe. These insects often appear in large numbers on porches and window screens, leading many to question the role of artificial light in their presence. This common observation suggests the bugs are strongly drawn to exterior lighting. The truth involves a specific behavioral response to light combined with a seasonal drive to find shelter.
Understanding Stink Bug Phototaxis
Stink bugs exhibit phototaxis, their automatic movement toward or away from a light source. Research confirms that adult BMSBs are positively phototactic, moving toward artificial light at night. This response is not uniform across all types of illumination, depending strongly on the light’s wavelength and color.
BMSBs are most drawn to shorter-wavelength light, including ultraviolet (UV) and visible light at the blue and white ends of the spectrum. Studies show that white light is the most attractive stimulus, followed by blue light. Conversely, longer wavelengths, such as yellow, orange, and red, are significantly less attractive.
Their vision is most sensitive to the green and UV ranges, with peak sensitivity around 519 nanometers (green) and 367 nanometers (UV). The insect’s life stage also affects this behavior, as adult males are often more attracted to light than females or nymphs.
Overwintering Behavior and Structural Entry
While light acts as an attractant, it is not the primary reason these bugs enter homes in the fall. The main motive for migration is the instinct to find a protected, warm place for overwintering, a dormant state known as diapause. This search for shelter typically begins in late summer and early autumn as temperatures drop.
Adult BMSBs seek out man-made structures like houses and sheds to hide in dry crevices for the winter. They often aggregate on the sun-warmed, south-facing sides of buildings before locating an entry point. They squeeze into cracks around window and door frames, utility penetrations, chimneys, or under siding.
The bugs are not actively feeding during overwintering, so their motivation is purely survival. Light sources likely serve as a beacon, guiding them to the general area of the structure. This combination of structural and light attraction leads to visible congregations near exterior fixtures.
Adjusting Exterior Lighting to Reduce Attraction
Homeowners can take steps to mitigate light-based attraction, especially during the peak migration season in the fall. The most effective strategy is to switch out exterior bulbs that emit highly attractive short-wavelength light. Mercury vapor lamps and bright white or cool-toned compact fluorescent lamps (CFLs) should be replaced.
Instead, opt for bulbs that emit longer wavelengths, which are less visible to the bugs. Yellow “bug lights,” high-pressure sodium vapor lamps, or warm-spectrum LED bulbs (those with a color temperature below 3000 Kelvin) are effective alternatives. These lights still provide illumination for humans but significantly reduce the visual cue that draws BMSBs toward the home.
Strategic placement and timing of lights can also minimize attraction. If possible, move lights away from direct entry points, such as mounting a lamp on a post a short distance from the front door. Utilizing motion sensors or timers to keep exterior lights off during late-night hours, a prime time for insect activity, further reduces the overall attraction.