Fall Home Invaders 2026: When They Come Inside

Between early September and early November, depending on where you live, and the spread is smaller than you would expect: the flights are cued by shortening days as much as by cold, so Georgia and Maine are only weeks apart rather than months. Ohio State Extension puts peak brown marmorated stink bug flight in late September or early October; the University of New Hampshire has them massing on buildings from about September 1st to 20th; the University of Kentucky has them entering Kentucky buildings in early to mid September. The state table on this page gives a computed date for each state.

They did not come in in January. They came in during the autumn and have been sitting in a wall void, an attic or a window frame ever since, not feeding and not moving. A warm spell, or simply the warmth of the room on the other side of that wall, brings a few out of dormancy, and they head toward light. That is why they turn up on curtains, lampshades and TV screens in midwinter. They are not breeding, and no new ones are arriving.

Ohio State University Extension gives the clearest published figure, for the multicoloured Asian lady beetle: adults are prompted to search for overwintering sites on the first day over 64°F after a significant drop in temperature, usually to near freezing. The University of Kentucky describes flights as heaviest on sunny days following cooler weather, when temperatures return to at least the mid 60s, and the University of Minnesota gives above 65°F. The pattern is a cold night followed by a mild sunny afternoon, and it is why the invasion happens on two or three specific days rather than gradually.

Not really, and it is worth being precise. Stink bugs, boxelder bugs and western conifer seed bugs do not bite, do not sting, do not carry disease and do not damage the house. Cluster flies carry no disease of medical importance, because their larvae parasitise earthworms rather than living in waste. Asian lady beetles are the one exception worth flagging: they can pinch hard enough to feel, and a 2007 paper in the Journal of Allergy and Clinical Immunology identified them as a seasonal indoor allergen, naming two allergen proteins, so a heavy infestation can matter for someone with asthma or allergies. For a healthy household, none of them is a danger.

No. This is the strongest consensus in the whole subject. Penn State Extension: "It is not advisable to use an insecticide inside after the insects have gained access to the wall voids or attic areas." It kills large numbers of them, and then carpet beetles arrive to feed on the accumulated bodies and go on to attack woollens and stored dry goods. Kentucky, Ohio State, Cornell, Maryland and Minnesota give the same advice, and indoor foggers and bug bombs are specifically discouraged. Vacuum what gets into the living space, and seal the outside next summer.

Once they are on the wall in numbers, sealing stops helping and starts trapping. The published deadlines are late summer, not autumn: the University of Minnesota says seal for boxelder bugs before the end of August and for Asian lady beetles by late September; the University of New Hampshire says caulk and seal before early September and screen attic vents before September 10th. Each state page here computes a date for that state.

Look at the shield behind the head rather than at the spots. The Asian lady beetle has a whitish shield carrying a black M, or a W depending which way up you view it, and the spots are useless because one species ranges from none to nineteen and from pale yellow to deep red. Native species such as the convergent lady beetle have a dark shield with pale converging marks. Ohio State, Cornell, Minnesota and Maryland all lead with the M.

The individuals that survive the winter leave in spring, once outdoor temperatures pass about 63°F, to feed and breed outside. They do not come back to the same house because they remember it; they come back because the house is still the warmest sheltered structure in the same landscape. The way to change that is exclusion in late summer, before the next flight.