Stink Bug Season in Westchester: How to Keep Them Out

Why Stink Bugs Descend on Westchester Every Fall

The brown marmorated stink bug (*Halyomorpha halys*) is a non-native invasive insect that arrived in the United States from East Asia in the late 1990s and has since become one of the most widely encountered fall pests throughout the Northeast. In Westchester County, the pattern is consistent: as temperatures begin to drop in September and October, stink bugs aggregate on the south and west-facing exteriors of homes in communities from Yonkers to Yorktown Heights, seeking entry points to overwinter inside the structure.

They are not dangerous and do not reproduce indoors. But when dozens or hundreds find their way inside a Westchester home and begin emerging from wall voids during winter warm spells, the invasion — and the odor of crushed insects — becomes a genuine quality-of-life problem.

The Aggregation Behavior

Stink bugs are phototaxis-driven: they are strongly attracted to warmth and sunlight reflected off building surfaces. On sunny September and October afternoons, the south and west facades of Westchester homes can be covered with stink bugs seeking entry. They navigate through gaps around window frames, door weatherstripping, HVAC penetrations, attic vents, and any other opening they can locate.

Once inside wall voids and attic spaces, they enter a semi-dormant state called diapause for the winter. When interior temperatures warm in late winter or early spring, they become active again and often emerge into living spaces — typically in large numbers over a short period.

Entry Points Specific to Stink Bug Invasion

Stink bugs are larger than mice and require larger gaps, but Westchester's older housing stock provides these reliably:

Window air conditioner gaps: Seasonal window AC units with poorly sealed edges are among the most reliable stink bug entry points. The foam insulation kits that ship with these units degrade over seasons and leave substantial gaps.

Chimney and fireplace dampers: An open or poorly sealed damper is a direct path into the living space. Even closed dampers often have gaps at the edges.

Attic vents: Deteriorated or improperly screened soffit and gable vents allow mass entry into attic space, which then provides access to interior wall voids.

Window and door weatherstripping: Compressed or deteriorated weatherstripping around any exterior opening leaves gaps that stink bugs navigate through.

The Fall Timing Window

The most effective intervention for stink bug prevention is before aggregation begins — ideally in mid-September in Westchester County, before the first significant cool evenings that trigger aggregation behavior. Two key actions:

Perimeter insecticide treatment: A professional fall perimeter application, targeting the exterior foundation, sill plates, window frames, and entry points, intercepts stink bugs before they can aggregate and seek entry. Applied by a licensed exterminator, this treatment significantly reduces the population that reaches the building exterior.

Sealing: Caulking around window frames, door frames, and utility penetrations, along with replacing deteriorated weatherstripping and screening attic vents, physically prevents entry for the individuals that reach the building.

What Not to Do Once They're Inside

If stink bugs are already inside your walls or emerging into living space, do not crush them — the defensive odor is significant and unpleasant in an enclosed space. Vacuum them up using a bag vacuum and dispose of the bag immediately outdoors. A DIY light trap (a shallow dish of soapy water under a desk lamp) can catch active individuals overnight.

For significant invasions — dozens or hundreds of stink bugs emerging over multiple days — professional treatment of the wall void and attic harborage sites is the most effective resolution.

BluesWay Pest Control provides professional stink bug prevention and elimination services for Westchester County homeowners. Call us at (914) 968-8404 to schedule a fall perimeter treatment before stink bug season peaks — effective timing makes the difference between a minor annoyance and a serious invasion.