Which insects are common fall invaders in homes?

UNH Cooperative Extension's own fact sheet is explicit about naming five species as the state's principal fall home invaders: the boxelder bug, the multicolored Asian lady beetle, the brown marmorated stink bug, the western conifer seed bug, and cluster flies — and it notes that the lady beetle, the stink bug, and the conifer seed bug are all relatively recent arrivals to New Hampshire, while cluster flies and boxelder bugs have been a familiar seasonal nuisance for longer. All five share the identical behavior pattern: massing on sun-warmed south- and west-facing exterior walls through September and into October, then squeezing through cracks, vents, and siding gaps to spend winter dormant. None of the five reproduce indoors, damage the structure, or pose a disease risk to people — this is a nuisance list, not a damage list, with one candid exception carved out below.

Every other insect on this roster is genuinely harmless beyond being a nuisance. The Asian lady beetle isn't quite. It can nip occasionally, it reflex-bleeds a foul, staining yellow fluid loaded with defensive alkaloids when disturbed or crushed, and it's a documented indoor allergen — clinical literature has recorded allergic rhinoconjunctivitis and asthma linked to indoor lady beetle exposure. That doesn't move it out of the 'fall invader' category, but it does mean the candid advice for this one species is slightly firmer than 'ignore it': vacuum rather than crush, and if someone in the household develops new respiratory or eye symptoms during a heavy lady beetle year, it's worth mentioning to a doctor.

Three more groups reliably show up more in fall, and they're worth naming here precisely because homeowners lump them in with the insects above — even though the underlying driver is different for each. Field and house crickets really fit the fall-invader pattern loosely: they wander toward buildings as nights cool and are drawn by exterior lighting, entering through the same unsealed gaps. Camel crickets, by contrast, are a moisture story — they show up in damp basements and crawlspaces year-round, tracked to humidity and prey rather than the calendar. House centipedes are similarly moisture- and prey-driven, present indoors whenever conditions are damp enough, not massing outside each fall and pushing in. And the fall spider surge is mostly an inside job — sexually mature males already living in the house leave their webs to search for females, rather than outdoor spiders fleeing the cold. Naming all three on this roster, and then immediately separating their mechanism from the true five, is the accurate version of this list — a hub that folds everything into one story isn't more helpful, it's just less accurate.

The reason the ID matters is that it changes the calendar you're working against. For all five UNH-named species, the single effective intervention is exterior exclusion — caulking, screening, sealing — finished before the entry window closes in early-to-mid October in southern New Hampshire. For camel crickets and centipedes, the fix is drying out the space, not sealing a wall against a fall migration that isn't happening. For spiders, it's decluttering harborage and excluding gaps year-round, since the population is largely resident rather than seasonal. Getting the ID right on this page is what routes a reader to the correct page for what to actually do next, rather than applying the cluster-fly playbook to a centipede problem it was never designed for.