Masses of black bugs with red-orange markings gathering on sunny walls in fall are box elder bugs. They cluster on warm south and west sides of the house, then slip inside to overwinter. They are harmless but conspicuous, and common wherever box elder and maple trees grow.
What’s most likely going on
Box elder bugs feed on box elder and maple seeds through the warm months, then congregate on warm walls in fall before entering wall voids to overwinter, re-emerging indoors on warm winter days.
What it means for your home
They do not bite, damage the home, or harm trees — the issue is the large staining clusters and their habit of wandering into living space all winter.
What to do next
We treat exterior harborage and aggregation sites and seal entry points, focusing the work in fall when they are gathering to come inside. You can read more in our Pest Library entry on box elder bugs, or head straight to our Box Elder Bug Control service.
Reviewed by Matthew — Salty Dog Pest Control. WSDA-licensed structural pest applicator (License #101709). Veteran- and family-owned, serving Whidbey Island, Fidalgo Island, and west Skagit County.
Frequently asked questions
Do these bugs cause damage?
No — they do not bite, damage the house, or meaningfully harm trees. They are strictly a nuisance in large numbers.
Why only on one side of my house?
They gather on the warmest sun-facing walls in fall before moving inside, which is the time to treat and seal.
Not sure what you’re dealing with? Call (360) 206-3293 for a free estimate over the phone, or browse the full Pest Library.
