Box elder bugs cover the sunny side of your house in fall because they’re looking for a warm place to spend the winter. As nights turn cold in September and October, they leave the box elder and maple trees they fed on all summer and gather on south- and west-facing walls that soak up afternoon heat. From there, they slip through small gaps around windows and trim into wall spaces and attics. Good box elder bug control starts before they show up, with sealed gaps and a treatment on the outside walls where they gather. Any that make it inside are best vacuumed up, never squashed.
You step outside on a warm October afternoon and the whole south wall looks like it’s moving. Hundreds of black bugs with red-orange stripes on their backs sit in the sun on your siding and crawl around the window frames. It looks alarming. It’s also one of the most predictable things that happens to homes every fall.
Why Box Elder Bugs Pick Your House
All spring and summer, box elder bugs feed on box elder seed and leaf juices, and sometimes on nearby maples. As days shorten and nights turn cold, they stop feeding and look for shelter. Out in the yard, that might mean loose tree bark or a pile of leaves. Your house is a big upgrade.
A wall that’s been in the sun all afternoon stays warm into the evening, and the gaps behind siding and trim lead into spaces that won’t freeze all winter.
Some homes get hit far harder than the house next door. A few things push yours to the top of the list:
- A female box elder tree (the kind that grows the winged seeds) in your yard or on the next lot
- Walls facing south or west, since those hold the most afternoon heat
- If the caulk (the rubbery seal around windows and trim) is cracked or your trim has pulled away from the siding, the bugs will find those openings first
- Torn window screens and worn door sweeps (the rubber or brush strip along the bottom of a door)
Do Box Elder Bugs Cause Damage?
Here’s the reassuring part. Box elder bugs don’t chew wood or wiring, and they won’t get into your pantry. They also don’t breed inside your home over the winter. They’re waiting out the cold, and in spring they head back outside to the trees.
That said, they can be a nuisance. Their droppings leave small reddish-orange spots on curtains and light-colored walls. Crush one, and you’ll get a bad smell and a stain that’s tough to wash out. They rarely bite, and when one does, it feels more like a pinch than anything that needs medical attention.
What surprises most homeowners is seeing them in January. A sunny winter day warms the wall space where they’re hiding; they wake up and wander toward the light. That’s how you end up with box elder bugs on the inside of a window while there’s snow on the ground.
Families from Grand Rapids to the Salt Lake Valley see this every year, and it usually means a good number of bugs moved into the walls back in the fall.
Box Elder Bug Control Starts Outside
Timing matters more than anything else with these bugs. Once they’re inside your walls, you can’t easily reach them. The best window for box elder bug control is late summer through early fall, before large clusters form on your siding.
Start by closing the openings they use to get in. Our guide on how to seal off your home from pests goes into more detail, but these are the spots we check first on a fall visit:
- Caulk the gaps around window and door frames, especially where trim meets the siding
- Torn screens and missing door sweeps are worth replacing before October
- Where pipes, cables, or a dryer vent pass through the wall, fill the gap around them
- Put fine mesh over attic and roof vents so bugs can’t crawl into the attic and work their way down
For clusters already sitting on your siding, a bucket of water with a few squirts of dish soap works better than most people expect. Pour or brush it straight onto the bugs. The soap breaks down their outer coating, and it eliminates most of the bugs it soaks. It won’t do anything for bugs already tucked behind the trim, so you’ll have to repeat it every warm afternoon until the weather turns.
Hosing them off the wall feels satisfying. The trouble is that they land in the grass, dry off, and climb right back up.
Some homeowners ask whether they should cut down the box elder tree in their yard. It can help, since female trees are the main food source. Box elder bugs can also fly in from trees down the street, so taking out one tree rarely solves the problem on its own.
Raking up the fallen seeds under the tree each fall is a small step that still reduces how many bugs grow up in your yard. If you’re curious about what draws them to certain trees, we cover that in our post on what box elder bugs eat.
What to Do When They Get Inside
Grab the vacuum. It’s the fastest, cleanest way to deal with box elder bugs on windowsills and walls. Use a hose attachment so you don’t crush them on the floor, and empty the canister or bag outside right away, or seal it in a trash bag before tossing it.
Skip store-bought treatments for wall spaces. Bugs that die inside your walls can attract carpet beetles, small beetles that feed on dead insects and then move on to wool rugs and clothing. You’d be trading one pest problem for another. Vacuuming the strays and sealing the outside of the house does much more good.
Box elder bugs also share the fall season with a few other bugs looking for winter shelter. If you’re seeing shield-shaped brown bugs mixed in, those are probably stink bugs. Our list of the most common fall pests can help you tell them apart.
How We Handle Box Elder Bugs
Two brothers started proof. Pest Control in 2015 with a purpose to give back, and we’ve spent every fall since then helping families get their walls back from box elder bugs. Our approach starts with an inspection of your home’s sunny sides, where we look for the exact gaps and cracked caulk the bugs use.
From there, we apply botanically-derived products to the outside walls and window frames where box elder bugs gather. We time those treatments for late summer and early fall, so the bugs encounter a treated surface before they can get in. All our products are EPA-registered, so you don’t need to worry about your kids or pets.
Our pest-free guarantee™ covers 30+ household pests, including box elder bugs. We visit on a regular schedule year-round, and if box elder bugs come back between scheduled visits, we come back too. Those re-service visits are unlimited.
If your siding is already crawling this October, it isn’t too late to cut down how many spend the winter in your walls. Call us at (888) 291-5333 or reach out through our contact page, and we’ll get a technician out before the next warm afternoon brings another wave.
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