Why are there stink bugs in my house in January?
They came in through gaps in September and October to overwinter in the attic or walls, and a warm day woke them up. They're trying to get back outside. Vacuum them; they aren't breeding indoors.
Stink Bugs, Asian Lady Beetles, and Boxelder Bugs
Reviewed by William "Willy" Vizcarrondo, NYS Certified Pesticide Applicator (C1825832). Updated September 23, 2026.
Quick facts
Brown marmorated stink bugs, multicolored Asian lady beetles, and boxelder bugs are the fall invaders. On the first warm afternoons after cold nights in September and October, they gather by the hundreds on the sunny side of Long Island houses and work their way into attics, wall voids, and window frames to spend the winter. None of them breed or feed indoors; they're just waiting for spring.
| Size | Stink bug about 2/3 inch; Asian lady beetle about 1/4 inch; boxelder bug about 1/2 inch |
|---|---|
| Color | Stink bug mottled brown, shield-shaped, with light bands on the antennae; lady beetle orange to red with variable black spots and a black W or M mark behind the head; boxelder bug black with red lines |
| Look-alikes | Native stink bugs and lady beetles, which don't invade in numbers; kissing bugs (not found here) |
| Where you'll find it | South- and west-facing walls in fall; attics, soffits, wall voids, behind baseboards, around window and door trim, ceiling lights and exhaust fans indoors |
| Active on Long Island | Invasion September through October; indoor sightings all winter on warm days; exit in March and April |
| Danger level | Nuisance and staining; lady beetles can bite; stink bugs smell when crushed |
Long Island season
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
They arrive in September and October, show up at windows and lights on warm winter days, and try to leave again in March and April.
How to identify it
A stink bug is shield-shaped, mottled brown, about two thirds of an inch long, with light and dark bands on the antennae and along the edge of the body (Penn State). An Asian lady beetle is a ladybug that varies from pale orange to deep red with anywhere from zero to 18 spots, and the tell is a black W or M shape on the white plate behind the head (Penn State).
A boxelder bug is black with thin red lines along the back and wings, and it comes from boxelder, maple, and ash trees. All three show up in the same places at the same time.
Signs you have them
- Dozens or hundreds of bugs on the sunny side of the house on a warm September afternoon
- Bugs squeezing under siding, into soffit gaps, and around window frames
- Bugs at windows, ceiling lights, and exhaust fans indoors in winter
- Yellow stains on walls and sills from lady beetles
- A cilantro-like or musty odor when stink bugs are crushed
Why it matters
They don't damage the house or breed inside, and Penn State says so plainly for stink bugs: they will not reproduce inside structures or cause damage. The problems are volume and mess. Tens of thousands of lady beetles can gather in one attic or wall void (Penn State), they bite occasionally, and they leak a yellow, foul-smelling fluid that stains walls and can raise a welt on skin.
Crushing or vacuuming large numbers of stink bugs releases their odor into the house (Penn State). On Long Island's North Shore, wooded lots and light-colored houses with a sunny south wall are the most-hit.
Can I handle it myself?
Yes, and the timing is everything. Exclusion is the real fix: seal cracks around windows, doors, siding, utility pipes, behind the chimney, and under the fascia with good silicone or silicone-latex caulk before September, and repair screens and vents (Penn State). Indoors, vacuum them rather than crushing them, and empty the bag outside.
Exterior sprays only help in a narrow window, late September into early October right before they congregate, because sunlight breaks the product down fast (Penn State). By November, spraying is pointless.
How Bobby Bugs treats it
A perimeter treatment of the sunny walls, soffits, and entry points in late September or early October, timed to the first cold nights, plus sealing the gaps we find. General insect treatment covers fall invaders.
Frequently asked questions
Do Asian lady beetles bite?
Occasionally, and it can pinch. They also leak a yellow fluid from their leg joints that stains and can irritate skin. Vacuum clusters instead of handling them.
When should I spray for stink bugs?
Late September to early October, just before they gather on the house, and only outside. Any later and it doesn't work; the product breaks down in sunlight and the bugs are already inside.
How do I keep them out next year?
Caulk every crack around windows, doors, siding, pipes, and the chimney before September, fix screens, and cover attic and soffit vents with fine mesh. Sealing works better than any spray.
Sources
Think you have fall invaders? Call (516) 509-6001 for a free written quote.