Why they show up every October
The stink bug most Maryland homeowners deal with is the brown marmorated stink bug, an invasive insect from East Asia that has been common across the mid-Atlantic for well over a decade. In summer it feeds on fruit trees, gardens, and ornamental plants. When the days get shorter and nights get cooler in September and October, adults start looking for a protected place to spend the winter.
To a stink bug, your house looks like a large, warm rock with plenty of cracks. They gather on the sunniest sides of the building, usually the south and west walls, and work their way into any gap they can find. Homes in Columbia that back onto wooded open space, common areas, or large gardens often see the most activity, because there are more bugs nearby when the weather turns.
The good news: stink bugs don't bite, don't carry disease, and don't breed inside your home over the winter. They don't eat wood, wiring, or fabric. The problem is the numbers, the smell when they're disturbed, and the fact that they keep appearing indoors on warm winter days when they wake up and wander toward light.
Where they get in
Adult stink bugs are about the size of a fingernail, but they're flat and can squeeze through surprisingly narrow openings. The most common entry points we find on Columbia homes are:
- Gaps around window frames, especially older windows and damaged screens
- Spaces where siding meets trim, corner boards, or the foundation
- Openings around utility lines, dryer vents, outdoor faucets, and cable entries
- Attic and soffit vents without intact screening
- Worn weatherstripping and door sweeps on exterior and garage doors
- Gaps around window air conditioners left in place for the season
What to do when they're already inside
Once stink bugs are inside wall voids and the attic, there's no spray that will reach all of them. The goal indoors is to remove the ones you see without making the problem worse:
- Don't crush them. That releases the odor they're named for, and it can linger on fabric and surfaces.
- Vacuum them up, ideally with a shop vac or a vacuum you can empty outside right away. The smell can stay in a regular vacuum for a while.
- Knock them into a jar of soapy water. The soap breaks the surface tension and they can't climb out.
- Skip foggers and bug bombs. They don't reach insects hiding inside walls and leave residue in your living space.
- Turn off unneeded lights near windows at night, since stink bugs move toward light when they become active.
Why timing and sealing matter more than spraying
The most effective stink bug control happens before they get inside. An exterior treatment applied to the walls, eaves, and entry points in late summer and early fall stops many of them from settling in. Sealing the gaps listed above keeps out the ones that land on the house anyway. Doing both together works much better than either one alone.
If you're reading this in late October and the bugs are already in, don't give up on prevention. Sealing still helps limit how many make it from the walls into your living space, and it sets you up for a much better fall next year. It also helps with other fall invaders, like ladybugs, boxelder bugs, and spiders, which use the same openings.
A simple way to find the gaps: walk around the house on a sunny afternoon in late September or early October and watch where stink bugs cluster. The spots where they gather and disappear, often a window corner, a vent, or a gap in the trim, usually point straight to the openings that need attention.
When to call a professional
A few stink bugs on the windowsill each week is normal for this area. It's worth calling a pro when:
- You're finding dozens of stink bugs indoors, or large clusters on exterior walls
- They keep appearing in the same rooms, which points to a specific entry point you can't locate
- The attic or a second-floor area has heavy activity that's hard to reach safely
- You want an exterior treatment timed correctly for next season
See our stink bug control service page for what a fall exterior treatment and sealing visit covers in Columbia, MD.