When black-and-red bugs start gathering on your siding, windows, or front door in fall, you may be dealing with boxelder bugs. These insects can appear in large numbers, especially on warm, sunny afternoons.

The good news? Boxelder bugs are mainly a nuisance. They don’t eat wood or cause the structural damage associated with pests like termites. Still, nobody wants a crowd of insects on their house or unexpected visitors indoors.

Here’s how to identify boxelder bugs, understand why they show up, and keep them outside.

What do boxelder bugs look like?

Adult boxelder bugs are roughly 12–14 mm long, with flat, elongated bodies. They’re mostly black, with red-orange lines along the body and wings.

Young boxelder bugs, called nymphs, are smaller and more noticeably red. Their dark wings develop as they mature.

You’ll often spot them clustered together on tree trunks, siding, brickwork, window frames, and other sun-warmed surfaces.

Why are boxelder bugs around my house?

Boxelder bugs feed primarily on the seeds and other parts of boxelder trees, also known as Manitoba maple. They may also feed on other maples.

As temperatures drop in late summer and fall, adults look for sheltered places to spend the winter. Homes offer plenty of hiding spots, including gaps behind siding and small openings around windows, doors, and utility lines.

South- and west-facing walls are especially attractive because they collect afternoon warmth. A gathering on your siding doesn’t necessarily mean bugs are already indoors, but it’s a good reason to check for entry points.

Are boxelder bugs harmful?

Boxelder bugs aren’t generally considered dangerous to people or pets, and they don’t reproduce inside homes. They also don’t infest stored food or eat building materials.

Their biggest drawbacks are the nuisance of having them indoors, an unpleasant odour when disturbed, and the stains they can leave when crushed.

Avoid handling or squashing them. Removing them gently is usually the cleaner approach.

How to keep boxelder bugs outside

The best long-term strategy is exclusion: closing the openings bugs use to enter your home.

Seal gaps and cracks

Inspect around window frames, door frames, siding joints, and places where pipes or cables enter the building. Use an appropriate exterior sealant to close accessible gaps.

Don’t block drainage openings, ventilation, or weep holes. Where these need protection, use a suitable screening solution that preserves their function.

Check screens and door seals

Repair damaged window screens and make sure they fit securely. Replace worn weatherstripping and install or adjust door sweeps where gaps allow insects inside.

Focus on sunny walls

Pay extra attention to the sides of your house where bugs gather. Their clustering can help you identify the areas that need a closer inspection.

Do this work before the main fall gathering begins whenever possible. Once insects are tucked behind siding or inside wall spaces, prevention becomes more difficult.

What to do if boxelder bugs are already indoors

For the occasional indoor bug, a vacuum is usually the simplest solution. Empty the collected insects promptly into a sealed bag and dispose of it in an outdoor garbage container. Follow your vacuum manufacturer’s instructions for emptying and cleaning the unit.

Avoid crushing bugs on walls, curtains, or furniture because they can stain surfaces.

You may see bugs reappear during warm winter days or in spring as they become active in their hiding places. Continue removing visible insects and address exterior entry points when conditions allow.

Should you spray for boxelder bugs?

Start with sealing, screening, and physical removal. These measures address how bugs enter and avoid unnecessary pesticide use indoors.

If you’re considering a pesticide, use only a product registered in Canada whose label specifically permits the intended pest, site, and application. Follow all label directions, including precautions for children, pets, plants, and nearby water.

Don’t apply outdoor products indoors or spray into electrical fixtures, outlets, or wall cavities. Avoid homemade pesticide mixtures, which can damage surfaces or plants and may not provide reliable control.

For large, recurring gatherings or difficult-to-reach entry points, a qualified pest-control professional can assess whether a targeted treatment is appropriate.

Will boxelder bugs come back next year?

They may. Nearby host trees, sunny exterior walls, and accessible shelter can make the same property attractive from year to year.

That doesn’t mean you need to remove a healthy tree. Start with practical building maintenance and exclusion. Keeping entry points sealed is useful against boxelder bugs and other occasional invaders, too.

The bottom line

Boxelder bugs can be annoying, but they’re usually manageable. Identify them correctly, seal the openings they use, repair screens and door seals, and vacuum any that make their way indoors.

A little preparation before fall is often the most useful step toward keeping these seasonal visitors outside, where they belong.