Stink bugs get into houses through surprisingly small gaps in the building exterior, driven indoors by cooling fall temperatures. An adult brown marmorated stink bug can squeeze through an opening as small as 3 by 7 millimeters, roughly the width of a pencil eraser. That means cracks around windows, gaps under doors, torn screens, and openings where pipes or wires pass through walls are all viable entry points.
Why They Come Inside in Fall
Stink bugs are overwintering insects. They don’t breed or feed inside your home. They’re looking for a sheltered spot to survive the cold months in a state of dormancy, similar to how ladybugs cluster inside walls and attics. Adults move to buildings on warm, sunny days in September and October, with flight activity peaking in the afternoon. The timing can vary from one day to the next, which is why you might see dozens on a Tuesday and none on a Wednesday.
Late in summer, stink bugs gather in large numbers on host plants like fruit trees, ornamental shrubs, and garden crops. When those gatherings happen close to a building, the bugs are far more likely to move onto the structure and eventually find their way inside. Once a few arrive, they release an aggregation pheromone, a chemical signal (separate from the defensive stink) that draws more stink bugs to the same spot. This is why infestations tend to concentrate on one side of a house rather than spread evenly.
The Entry Points They Use
Because they can fit through a 3-by-7-millimeter hole, stink bugs exploit gaps most homeowners never think about. The most common entry points include:
- Window and door frames: small cracks where caulk has aged or weatherstripping has compressed
- Utility penetrations: holes where plumbing, gas lines, electrical conduits, or cable wires pass through exterior walls
- Attic and roof vents: unscreened louvres or vents with damaged mesh
- Soffits and fascia: gaps where the roofline meets the siding
- Outdoor faucets: spaces around hose bibs and spigots
- Chimneys: uncapped or poorly sealed chimney openings
Once they’re inside the wall cavity or attic, stink bugs settle into crevices and go dormant. You often won’t notice them until a warm winter day or the arrival of spring “wakes” them. Disoriented by indoor heat, they wander toward light and end up buzzing around windows, lamps, and ceiling fixtures instead of heading back outside.
What Attracts Them to Your House
Two factors draw stink bugs to a building before they ever find a crack to crawl through: warmth and light. South- and west-facing walls absorb the most afternoon sun, making them the most common landing zones. If your home’s sunny side also has a porch light or illuminated windows, it becomes even more attractive. Stink bugs are strongly drawn to light in late summer and early fall, which is why they also swarm convenience stores, gas stations, and lit-up commercial buildings.
The aggregation pheromone compounds the problem. A handful of early arrivals on your siding can chemically recruit dozens or hundreds more. Homes near agricultural fields, orchards, or wooded areas tend to see the worst infestations because large populations of stink bugs are already congregating on nearby plants.
How to Seal Them Out
Physical exclusion is the single most effective strategy, and it needs to happen before September. Once the bugs are already inside your walls, sealing won’t help until the following year.
Use high-quality silicone or silicone-latex caulk to seal cracks around windows, doors, and siding joints. Fill gaps around utility penetrations with steel wool, copper mesh, or urethane expandable foam. Install door sweeps on every exterior entrance. For attic vents, roof vents, and crawl space openings, cover the opening with quarter-inch wire mesh (hardware cloth) and back it with fine insect screening for extra protection. Repair or replace any torn window screens, paying attention to the corners where mesh pulls away from the frame.
The goal is to eliminate every opening larger than a few millimeters. It’s tedious work, but it’s the only approach that reliably reduces the number of stink bugs getting inside year after year.
Why Pesticides Often Don’t Work
Indoor pesticides are largely ineffective against stink bugs. The bugs are dormant inside walls and voids where sprays can’t reach them, and by the time they emerge into living spaces, killing them one by one with chemicals is no more efficient than simply removing them. Outdoor perimeter treatments can help, but timing is critical. They need to be applied before the bugs begin landing on the building in early fall, and residual effectiveness drops as the product degrades from sun and rain.
Removing Stink Bugs Already Inside
If stink bugs are already wandering through your rooms, the priority is getting them out without triggering their defensive odor. Crushing or startling them releases the smell, which can linger on skin, fabric, and surfaces.
A simple vacuum cleaner works well for picking up individuals or small clusters. Use a handheld vacuum or attach a stocking over the end of the hose (secured with a rubber band) so you can dispose of them outside without them stinking up the vacuum canister. For larger numbers, researchers at Virginia Tech found that a homemade light trap outperformed commercial options by a wide margin. Fill a foil roasting pan with water and a squirt of dish soap, then set a desk lamp directly over it in a dark room. The light draws the bugs in, and the soapy water traps them. In testing, this setup caught 14 times more stink bugs than store-bought traps costing up to $50.
Flushing individual bugs down the toilet or flicking them into a jar of soapy water also works without releasing much odor. The key is avoiding any method that squishes them against a surface.