Pennsylvania is ground zero for the brown marmorated stink bug, an invasive species first identified in the United States in Allentown, PA, in 1998. Since then, these shield-shaped insects have spread to every county in the state and become one of the most recognizable household nuisances for Pennsylvania residents. They don’t bite, sting, or cause structural damage, but they invade homes by the hundreds each fall and release a pungent odor when disturbed or crushed.
Why Pennsylvania Has So Many Stink Bugs
The brown marmorated stink bug is native to East Asia and arrived in Pennsylvania with no natural predators to keep its population in check. The state’s climate, with warm summers and cold winters, drives the bugs’ behavior in a predictable cycle: they feed and reproduce outdoors during the growing season, then seek shelter inside structures as temperatures drop in the fall. Pennsylvania’s mix of agriculture, suburban development, and wooded areas creates ideal habitat, giving stink bugs both food sources and overwintering sites in close proximity.
The species has since spread to more than 45 states, but Pennsylvania remains a hotspot. The mid-Atlantic region’s particular combination of humidity, crop diversity, and building density means homeowners here deal with larger invasions than most of the country.
How to Identify Them
Brown marmorated stink bugs are roughly the size of a dime, about 14 to 17 millimeters long, with a distinctive shield shape. Their mottled brown coloring helps them blend in against tree bark and siding. The easiest way to confirm you’re looking at this species (rather than a native stink bug) is to check for two features: alternating light and dark bands along the edges of the abdomen, and smooth, white bands on the antennae. Native stink bugs in Pennsylvania, like the green stink bug, lack these banding patterns.
The “stink” comes from glands on the underside of the thorax that release a chemical containing compounds similar to those found in cilantro. The smell is often described as a sharp, herbal, slightly rotten odor. It’s a defense mechanism, and crushing or vacuuming the bugs without precautions will trigger it.
When They Show Up in Your Home
Stink bugs follow a reliable seasonal pattern in Pennsylvania. From late May through September, they’re outdoors feeding on plants and laying eggs. A single female can lay 250 or more eggs in a season, deposited in clusters of 20 to 30 on the undersides of leaves. Adults and nymphs feed throughout the summer, and by late August the new generation of adults begins looking for overwintering sites.
The fall invasion typically starts in mid-September and peaks in October, though warm spells in early November can extend it. Stink bugs are drawn to the sunny, south- and west-facing sides of buildings, where they crawl into any gap they can find: cracks around window frames, tears in screens, gaps under doors, openings around utility pipes, and spaces behind siding. They’re not trying to eat anything in your home. They enter a dormant state called diapause and simply wait out the winter inside your walls, attic, or crawl spaces.
On warm winter days and again in spring (typically March through April), dormant stink bugs become active and start appearing indoors. They’re disoriented and drawn to windows and lights. This is the second wave of annoyance, and it can last several weeks as bugs emerge gradually from their hiding spots.
Damage to Gardens and Crops
Stink bugs feed by piercing plant tissue with their needle-like mouthparts and sucking out the juices. This feeding style causes damage that’s often worse than it looks on the surface. On tree fruits like apples and peaches, it creates a characteristic pitting and distortion called “cat facing,” which makes the fruit unsellable even though it’s technically still edible. Pennsylvania’s apple and stone fruit industries have been hit particularly hard.
In home gardens, the damage shows up differently depending on the plant. Tomatoes and peppers develop spongy, discolored patches and internal tissue breakdown. Beans and okra get scarred, sunken areas and deformed pods. Stink bugs also feed on corn, soybeans, grapes, raspberries, and a long list of ornamental plants and weeds. If you’re growing any of these in Pennsylvania, stink bugs are a seasonal reality.
For commercial agriculture, the economic impact has been severe. In the early 2010s, mid-Atlantic apple growers reported losses exceeding $37 million in a single season. The problem has stabilized somewhat as growers adopted management strategies, but stink bugs remain one of the most damaging agricultural pests in the region.
Keeping Them Out of Your Home
Physical exclusion is the most effective long-term strategy, and the work needs to happen before stink bugs start moving in, ideally by late August or early September. Focus on the exterior of your home:
- Seal cracks and gaps around windows, doors, siding, utility pipes, and behind chimneys with silicone or silicone-latex caulk.
- Repair or replace damaged screens on windows, doors, and attic vents. Even small tears are large enough for stink bugs to squeeze through.
- Install door sweeps on all exterior doors, including garage doors.
- Cover vents and openings with fine mesh screening, particularly soffit vents and weep holes in brick.
These steps also help with other fall invaders like ladybugs and boxelder bugs. The investment in caulk and screening pays off over multiple seasons.
Exterior insecticide sprays applied around the foundation, windows, and eaves in September can reduce the number of bugs that make it inside. Look for products labeled for stink bugs and follow the directions for perimeter treatment. These sprays degrade over time, so a single application in early to mid-September, timed before the main invasion wave, gives the best results. Spraying after bugs are already inside your walls won’t help.
Removing Stink Bugs Indoors
Once stink bugs are inside, the goal is removal without triggering the smell. Crushing them is the worst option. A vacuum cleaner works, but use a shop vac or a vacuum with a bag you can seal and discard immediately. Standard bagless vacuums will smell for weeks.
For smaller numbers, the simplest method is to flick or gently sweep them into a container of soapy water. The soap breaks the surface tension of the water, so the bugs sink and drown quickly without releasing much odor. A wide-mouth jar or plastic container kept near a window works well during the spring emergence when a few appear each day.
For larger infestations, Virginia Tech researchers found that a homemade light trap outperforms commercial options by a wide margin. The setup is simple: fill an aluminum foil roasting pan with water and a squirt of dish soap, then position a desk lamp directly over the pan in a dark room. The light attracts the bugs, they fly toward it, hit the water, and drown. In testing, this homemade trap caught 14 times more stink bugs than store-bought traps costing up to $50, and it’s completely pesticide-free.
Indoor insecticide sprays are not recommended. They won’t reach bugs hiding inside walls, they leave residue on surfaces you touch, and dead bugs trapped in wall voids can attract other pests like carpet beetles.
Natural Predators Catching Up
One reason stink bug populations exploded in Pennsylvania was the complete absence of natural enemies. That’s slowly changing. A tiny parasitic wasp from Asia that targets stink bug eggs has been found establishing itself in Pennsylvania on its own, likely arriving as a hitchhiker. This wasp lays its eggs inside stink bug eggs, destroying them before they hatch. Researchers at Penn State and USDA have been studying and, in some areas, releasing these wasps as a biological control measure.
Native predators have also started adapting. Birds, spiders, and predatory insects that initially avoided stink bugs have gradually begun feeding on them. These biological controls won’t eliminate stink bugs from Pennsylvania, but they’re contributing to a slow, steady reduction in peak populations compared to the worst years of the early 2010s. For homeowners, that means the annual fall invasion is still very real but, in many areas, somewhat less overwhelming than it was a decade ago.