Fall Home Invaders in North Dakota: 2026 Timing

The main entry week in North Dakota lands around September 24 in a typical year, with insects massing on walls from about August 31 and stragglers still moving until roughly October 18. We compute those dates from day length at Fargo and the city's median first freeze of September 28. Any single year runs a week or two either side, because the flights only happen on the right afternoons.

They did not just get in. They came in during the autumn, settled into a wall void, attic or window frame, and have been sitting still ever since. A warm spell, or just the warmth of the room on the other side of that wall, brings a few out of dormancy and they walk toward the light, which is your window and your lamp. They are not feeding, not breeding, and not multiplying inside the house. University of Kentucky Entomology is explicit that the adults overwinter unmated and do not reproduce indoors.

Finish by about August 17, which is two weeks before they typically start massing here. Every published exclusion timing says the same thing in different words: University of Minnesota Extension 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. Sealing after they are in the walls does not remove them, and it can seal them in.

Look behind the head, not at the spots. The multicoloured Asian lady beetle has a whitish shield there marked with a black M, described by Ohio State Extension as "a black regularly to irregularly shaped M or W, depending upon whether the beetle is viewed from the front or from the rear". Spot count is useless: this one species ranges from no spots to nineteen, and from pale yellow through orange to deep red. Native species such as the convergent lady beetle have a dark shield with pale converging marks, not a white one with an M.

They can pinch. Ohio State Extension notes consistent reports of biting, particularly where a beetle gets trapped between skin and clothing, and University of Minnesota Extension says some can bite hard enough to break the skin, causing minor and short lived discomfort. There is also documented allergy: a 2007 paper in the Journal of Allergy and Clinical Immunology described the Asian lady beetle as a new seasonal indoor allergen and identified two allergen proteins, Har a 1 and Har a 2. That matters if someone in the house has asthma or seasonal allergies. For everyone else these are a nuisance, not a health threat, and they carry no disease.

No, and this is the most important thing on this page. 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." The reason is not squeamishness. It works well enough to kill hundreds or thousands of insects in the void, and then carpet beetles arrive to feed on the dead ones and go on to attack woollens, stored dry goods and other natural materials in the house. University of Kentucky, Ohio State, Cornell, Maryland and Minnesota all give the same advice. Indoor foggers are specifically discouraged.

No to both, for all four. They do not chew wood, they do not nest, they do not lay eggs indoors, and they cannot start a population in your walls. The damage is to fabric and paint, from staining: crushed stink bugs and boxelder bug droppings mark surfaces, and Asian lady beetles bleed a yellow fluid from their leg joints when handled that can stain permanently. That is the case for vacuuming rather than swatting.

Cluster flies, almost certainly, and no. Their larvae are parasites of earthworms, so unlike house flies and blow flies they have no connection to garbage or waste, and Penn State Extension states they are not known to carry any diseases of medical importance to humans. They overwinter in attics and upper wall voids and gather at windows on warm winter days, which is why they seem to appear from nowhere in February.