The Brown Marmorated Stink Bug (Halyomorpha halys), or BMSB, is a shield-shaped insect native to Asia that has become a widespread agricultural pest. These bugs use piercing-sucking mouthparts to feed on a wide variety of plants, causing significant economic damage to crops. As temperatures drop in the fall, adult stink bugs seek sheltered locations to enter diapause, a form of insect hibernation, often congregating inside homes to overwinter. While they do not bite or sting, their tendency to invade in large numbers and release a pungent odor when disturbed makes them undesirable houseguests. Understanding the conditions and substances these insects actively avoid offers the best path to non-chemical management and prevention.
Aromatic and Olfactory Deterrents
Stink bugs navigate and communicate using chemical signals. Strong, foreign odors disrupt their sensory systems, creating an environment they choose to avoid. Essential oils containing potent volatile compounds are effective deterrents because their intense aromas interfere with the insect’s chemoreceptors. Oils such as spearmint, peppermint, lemongrass, and clove are frequently cited for their repellent properties.
To deploy these odor-based defenses, homeowners can create simple spray solutions by diluting essential oils with water and a small amount of dish soap to help the oil emulsify. This mixture can be lightly misted around known entry points like window frames, door seals, and vents to create an aromatic barrier. Placing cotton balls soaked in concentrated clove or peppermint oil inside window sills or near cracks is another localized method of exclusion.
Pungent compounds found in common herbs can also create a less appealing habitat for the BMSB. Crushed garlic cloves or a mixture of garlic powder and water can be applied to exterior surfaces where the bugs tend to gather. The strong scent of dried cloves can be sprinkled on exterior window ledges and doormats, providing a passive repellent. While some oils like rosemary, thyme, or tea tree oil may cause direct contact mortality, their primary function in prevention is to repel them from entering a space.
Environmental Conditions They Avoid
Stink bugs are highly sensitive to temperature and moisture, avoiding conditions that are too cold, exposed, or dry for overwintering. As autumn approaches, they are drawn to the warmth radiated by sun-drenched surfaces, typically the south and west walls of buildings. They seek entry into protected voids. Once inside, they look for cool, dry spaces like attics, wall voids, and behind baseboards to maintain a low metabolic rate for the winter.
The most effective long-term strategy involves mechanical exclusion, which eliminates the protected habitat they seek. This requires a thorough inspection of the building exterior to seal all potential entry points before the first cold snap. All cracks around doors, windows, utility pipes, and chimneys should be sealed using high-quality silicone or silicone-latex caulk. Damaged window and door screens must be repaired or replaced, as even small tears provide an adequate route for the bugs to squeeze through.
Reducing the availability of outdoor overwintering sites near the home is beneficial. Stink bugs in nature shelter under loose bark, in woodpiles, or beneath ground debris. Removing piles of firewood, leaf litter, and other debris from the immediate perimeter of the house reduces the local population seeking shelter. Proper exterior maintenance makes the home less attractive, forcing the insects to find less-ideal locations for their winter diapause.
Direct Contact and Physical Irritants
For immediate removal of visible stink bugs, substances that cause physical harm or irritation upon contact are effective. Unlike passive aromatic deterrents, these methods require the solution or material to touch the insect directly. Soapy water is a widely used solution because the detergent quickly compromises the insect’s protective outer layer, the cuticle.
The soap breaks down the waxy coating on the exoskeleton, which retains the insect’s internal moisture, leading to rapid dehydration or desiccation. The solution also disrupts the surface tension of the water, allowing it to easily enter the insect’s spiracles, the small respiratory openings on its body, causing suffocation. A simple mixture of water and liquid dish detergent, sprayed directly onto the bug, will cause it to drop and quickly perish.
Another physical irritant is food-grade diatomaceous earth (DE), a naturally occurring powder composed of the fossilized remains of microscopic aquatic organisms. The powder’s particles are microscopic and abrasive, damaging the stink bug’s exoskeleton upon contact. This abrasion causes the insect to lose body moisture, leading to desiccation and death. Diatomaceous earth is most effective in dry conditions and should be applied as a fine dust in cracks and crevices where the bugs crawl.
Natural Predators and Biological Controls
The BMSB population in North America is partially kept in check by a range of native generalist predators, though these are often insufficient to control large infestations. Spiders, praying mantises, and some species of birds prey on the adult stink bugs and their young. Certain native insects, including some species of wasps and predatory stink bugs, also attack the eggs and nymphs of the BMSB.
A primary biological control agent is the samurai wasp, Trissolcus japonicus, a tiny parasitic wasp that specifically targets stink bug eggs. The female wasp lays her eggs inside a stink bug egg mass, and the developing wasp larva consumes the host, preventing the stink bug from hatching. In its native Asian range, this parasitoid is effective, destroying a significant percentage of BMSB egg masses.
The samurai wasp was accidentally introduced into the United States and has established itself in several regions, offering a long-term solution to controlling the pest. Researchers are studying its natural spread and effectiveness. Its presence is a significant factor in balancing the BMSB population. While general predators offer incidental control, the samurai wasp represents a specialized, targeted mechanism that helps suppress the population at the earliest stage of its life cycle.