Every September the south and west walls of houses from Merrill to Chiloquin turn into insect sunbathing decks. Boxelder bugs come off the boxelder maples that line older Klamath Falls streets; elm seed bugs come off the Siberian elms planted across the basin for shade; both are looking for a warm crack to spend the winter in, and they find it in siding gaps, window frames, and attic vents. They don't bite, breed indoors, or damage the house. They are simply everywhere, and a licensed local pest operator who times this season every year calls back with a free quote for keeping them outside.
Who's on the wall
Boxelder bugs are the black-and-red ones, half an inch long, familiar to anyone who grew up in the basin. Elm seed bugs are smaller, rusty brown with a black head, newer to Oregon and now well established here; OSU Extension's Klamath office fields samples of them every spring and fall, and they have the same habit of clustering on siding and slipping indoors when the sun hits. Brown marmorated stink bugs are the shield-shaped ones that show up in the curtains and release that smell when disturbed. Cluster flies are the slow, large flies that appear at upstairs windows on warm winter days after overwintering in the attic. Ladybird beetles do the same thing by the hundreds. None of them is a health issue; all of them are a patience issue, and the fix is the same family of work.
Timing is most of the job
The window is narrow: a residual exterior treatment on the sunny walls, around window and door frames, at the soffit line, and along the foundation in late August or early September — before the first cold nights send the bugs looking — does more than three treatments in October. Pair it with exclusion: caulking the gap where siding meets trim, screening attic and crawlspace vents, sweeps under garage-side doors. Indoors, the honest advice from any licensed operator is a vacuum, because spraying inside a house for bugs that don't feed there accomplishes little. In a bad seed-bug year the pressure returns in spring when the overwintered adults leave the walls, and a second perimeter visit then is worth having.
The trees, and the program
You can reduce the population by removing the host tree, which is a drastic trade of shade for peace and rarely worth it; raking and disposing of fallen elm seeds under the trees, and keeping firewood and mulch away from the walls, helps more than people expect. Most households in Klamath Falls and Altamont handle this as the fall visit of a recurring program for Klamath County, since the same exterior treatment also gets ahead of the fall spider migration and the first mice. Describe the house, which walls get the sun, and what trees are nearby, and the quote comes back free.