Why are stink bugs in my house every fall?

A sunny wall in September is a signal. The brown marmorated stink bug is an introduced species that spends summer on trees and crops, and as days shorten the adults head for shelter. Penn State's description is that they begin to search for overwintering sites starting in September through October and are attracted to the outside of houses on warm fall days in search of protected overwintering sites. South- and west-facing walls, especially light-colored ones, collect them by the dozens on a warm afternoon, and from there they find the gap behind the siding, the space around a window frame, an unscreened attic vent or the crack under a door. Once inside a wall void or attic they go still for the winter.

Because your house is warm. Stink bugs tucked into wall voids and the attic don't stay put; a run of warm days, or the heat coming on, wakes some of them, and Penn State notes they emerge from cracks under or behind baseboards, around window and door trim, and around exhaust fans or lights in ceilings. That's the one on the lampshade in January and the one buzzing at the window in February. Penn State is clear that they will not reproduce inside structures or cause damage; the ones you see are the same ones that came in last fall. Crushing them releases the smell, and Penn State notes crushed bugs can cause skin irritation in some people, so the vacuum is the tool.

Sealing before they arrive, vacuuming after. Penn State's recommended control is to seal entry points with good quality silicone or silicone-latex caulk before fall, around windows, doors, siding joints, utility penetrations and the chimney, along with screening vents and repairing screens. Once they're inside, use a vacuum to remove them, with the caveat that the vacuum may smell of stink bugs for a while; a stocking inside the hose caught with a rubber band keeps them out of the canister. Penn State notes indoor sprays are ineffective and not recommended, because they don't stop the ones still in the walls from emerging. A perimeter treatment on the outside of the house in early fall, at the windows, eaves and siding, cuts down how many get in.

The stink bug wave hits the whole island in late September and October, and the houses that get it worst are the ones with big sunny south walls, older windows and vinyl siding with open ends, from Massapequa and Levittown to Huntington, Smithtown and the North Fork. They come out of the ceiling light fixtures all winter, and Penn State notes the adults reappear in late April to mid-May heading back outside. Bobby Bugs does an exterior treatment in early fall and points out the gaps that need caulk and screen; fall invader work is general insect work and carries no guarantee.