The brown marmorated stink bug is an invasive pest now established across Michigan, showing up in homes every fall and damaging crops from apples to soybeans. Originally from East Asia, this shield-shaped insect has spread throughout the state since its arrival, and most Michigan residents encounter it when clusters appear on exterior walls in September and October before moving indoors for winter.
How to Identify Them
Brown marmorated stink bugs are mottled brown, shield-shaped, and roughly half to three-quarters of an inch long. The easiest way to tell them apart from native stink bug species is by looking at the legs and antennae, which have alternating brown and white bands. The edges of the abdomen also show a distinctive black and white pattern that’s visible without magnification if you look closely.
Young stink bugs (nymphs) look quite different from the adults. They’re smaller with orange to red coloring, so you might not immediately recognize them as the same insect. By late summer, they’ve matured into the familiar brown adults that begin congregating on sun-warmed exterior walls.
When They Enter Michigan Homes
Stink bugs don’t breed indoors. They’re looking for a warm, dry place to spend the winter, a behavior called overwintering. In Michigan, this process starts in September and October when adults gather in large numbers on the sunny sides of buildings, barns, and houses. If you notice clusters on your exterior walls during those months, expect to find them inside later in the season.
Once inside, they tuck into wall voids, attics, and gaps around window frames, entering a dormant state. They become visible again in late winter and early spring when warming temperatures rouse them. That’s when homeowners often find stink bugs crawling on windows and walls, disoriented and sluggish, trying to find their way back outside. This two-phase pattern (fall invasion, spring emergence) is why many people feel like they’re dealing with stink bugs year-round even though the insects are only active for part of that time.
Are They Harmful to People?
Stink bugs don’t bite or sting. They’re not venomous and they don’t carry diseases. The main nuisance is the smell: when disturbed or crushed, they release a pungent chemical from glands on their abdomen that most people describe as a sharp, cilantro-like odor. This defensive spray can also cause mild skin irritation in some people, similar to contact dermatitis. If the fluid gets in your eyes, it can cause temporary irritation to the cornea, so avoid rubbing your eyes after handling them.
Eating stink bugs is a different story entirely. While this isn’t a typical concern for most Michigan residents, a case series of 28 patients who consumed stink bugs documented symptoms including severe vertigo (in 89% of cases), tremors (82%), vomiting (64%), and disorientation. Symptoms appeared 4 to 6 hours after ingestion. This is worth knowing if you have young children or pets who might put one in their mouth, though serious harm from a single accidental encounter is unlikely.
Crop Damage Across Michigan
For Michigan’s agricultural sector, brown marmorated stink bugs are a serious economic threat. They feed by piercing fruit and plant tissue with needle-like mouthparts, leaving behind dimpled, discolored spots that make produce unsellable. Feeding damage has been recorded in tomatoes, sweet peppers, raspberries, apples, peaches, pears, cherries, corn, and soybeans. Early in the growing season, they target apple, cherry, and pear trees in particular.
The scale of damage can be staggering. In neighboring mid-Atlantic states where the pest established earlier, commercial farmers using standard pest management still saw a minimum of 25% of fruit per tree damaged by stink bug feeding, with losses reaching 90% in apples and pears. Michigan’s fruit industry, one of the largest in the country, faces similar risk as populations grow.
Keeping Them Out of Your Home
Prevention works far better than removal. The goal is to seal entry points before September, when stink bugs start scouting for winter shelter. Focus on three areas: doors, windows, and foundation cracks. Check weatherstripping around all exterior doors and replace any that’s worn or gapped. Inspect window screens for tears and make sure frames sit flush. Caulk visible cracks in your foundation, and pay attention to spots where utility pipes or wires enter the house, as these are common entry points.
Attic vents, chimney flashing, and soffits are also vulnerable. Hardware cloth or fine mesh screening over attic vents can block access without reducing airflow. The investment of an afternoon sealing gaps in late August can save you months of dealing with stink bugs indoors.
Removing Stink Bugs Indoors
If stink bugs are already inside, the key rule is simple: don’t crush them. Squashing releases their defensive odor, which lingers and can stain surfaces. A vacuum cleaner works well for picking up individuals or small groups. Use a handheld vacuum or a shop vac you can empty outside, since the smell will transfer to whatever bag or canister collects them.
For larger numbers, researchers at Virginia Tech found that a homemade trap outperformed commercial options costing up to $50. Fill a foil roasting pan with water and a squirt of dish soap, then place a desk lamp directly over it in a dark room. The light attracts the bugs, and the soapy water breaks the surface tension so they sink and drown. In testing, this setup eliminated 14 times more stink bugs than store-bought traps, and it’s completely pesticide-free.
Avoid using insecticide sprays indoors. They’re largely ineffective against overwintering stink bugs hidden in wall voids, and spraying inside creates chemical exposure for your household without solving the underlying entry problem.
Biological Control Efforts in Michigan
Michigan is actively fighting brown marmorated stink bugs with a natural enemy from their native range: the samurai wasp. About the size of a sesame seed, this parasitic wasp lays its eggs inside stink bug eggs, destroying them before they hatch. In Asia, samurai wasps attack up to 80% of stink bug eggs. Native North American parasitoid wasps, by comparison, manage less than 10%.
The samurai wasp was first discovered in Michigan in 2018, likely arriving accidentally in shipped egg masses. Since then, Michigan State University researchers have reared and released over 27,000 samurai wasps across 34 sites in the state. In 2021 alone, 20,000 wasps were released. The results are encouraging: researchers recaptured samurai wasps at previous release sites from 2019 and 2020, confirming that the wasps are successfully overwintering and maintaining populations years after release. This long-term establishment is critical, because it means the biological control is self-sustaining rather than requiring repeated releases indefinitely.
The samurai wasp poses no risk to people, pets, or other beneficial insects. It’s highly specialized, targeting stink bug eggs almost exclusively. As populations build across Michigan, the hope is that they’ll provide a meaningful check on stink bug numbers in both agricultural and residential settings.