Are Boxelder Bugs Harmful?

No, boxelder bugs are not harmful to people, pets, or your home. They do not sting, they do not spread disease, and they almost never bite. Still, when hundreds of them cover your sunny siding in late September, it is easy to worry.

In Thurston County, the bug you are seeing is the western boxelder bug, and fall is when it looks for a warm place to spend the winter.

Every fall, the team at Bigfoot Pest Management hears from Olympia, Lacey, and Tumwater homeowners asking the same question: Are boxelder bugs harmful?

Below, we cover what these bugs are, the small problems they do cause, why they pick your house, and how to keep them out.

What Are Western Boxelder Bugs?

Western boxelder bugs (Boisea rubrolineata) are the boxelder bugs that live in western Washington. They are true bugs, not beetles. They feed on the seeds of boxelder, maple, and ash trees.

Here is how to spot one:

• Size: Adults are about 1/2 inch long.
• Color: They are dark gray to black with thin red lines on the back and along the wing edges.
• Belly: The underside is orange-red. You will see it when they fly.
• Young bugs: Nymphs are bright red and have no wings.

Most national articles describe the eastern boxelder bug. Our western species looks and acts much the same, but its red markings are thinner. In the Northwest, western boxelder bugs have one generation per year.

Boxelder Bugs vs. Common Look-Alikes

Several fall bugs get mixed up with boxelder bugs. This quick chart can help.

Bug	Size	Key marks	Harmful?
Western boxelder bug	About 1/2 inch	Black with thin red lines; red nymphs	Nuisance only
Western conifer seed bug	About 3/4 inch	Brown, flat, leaf-shaped flaps on back legs	Nuisance only
Brown marmorated stink bug	About 5/8 inch	Shield shape, white bands on antennae	Nuisance, bad smell
Kissing bug	Over 1 inch	Long, cone-shaped head	Not known to live in Washington

Are Boxelder Bugs Harmful to Humans?

Boxelder bugs are not harmful to humans. According to the National Pesticide Information Center, they do not sting and do not spread disease.

They are not known to bite people. In rare cases, a trapped bug may pinch skin in self-defense. That can leave a small red spot, a lot like a mosquito bite.

Their mouthparts are made to pierce seeds and suck plant juice. They do not feed on blood, and they have no venom.

Some people worry that boxelder bugs are kissing bugs. The Washington State Department of Health says the kissing bugs that carry Chagas disease are not known to live in Washington.

Kissing bugs are also much larger, at more than an inch long.

Are Boxelder Bugs Harmful to Pets?

Boxelder bugs are not harmful to pets. The University of California IPM program notes that they do not injure people or pets. Their bright red and orange colors warn birds and other animals that they taste bad. Most dogs and cats lose interest fast after one try.

If your pet eats a large number of any bug and seems sick, call your vet to be safe.

Are Boxelder Bugs Harmful to Plants and Trees?

Boxelder bugs cause only minor plant damage. They suck juice from seeds, leaves, and young twigs. This can leave small yellow spots or cause a few leaves or fruits to grow a little misshapen. Healthy trees are not seriously hurt.

Their favorite host is the female (seed-bearing) boxelder tree. Maples and ash come next, and they sometimes visit fruit trees. Boxelder bugs are native to North America, so they are not an invasive species.

Are Boxelder Bugs Good for Anything?

Yes, boxelder bugs play a small role in a healthy yard. They help recycle nutrients by feeding on fallen seeds. Spiders, some birds, and other insects eat them, especially the young nymphs in spring and summer.

That is one reason pest pros do not try to wipe them out across a whole neighborhood. The goal is simple: keep them outside, where they belong. A few boxelder bugs on a tree trunk in July are nothing to worry about.

The trouble starts in fall, when they move from the trees to your walls. A plan that focuses on your house, not the whole yard, protects your home and leaves the rest of nature alone.

Can Boxelder Bugs Damage Your Home?

Boxelder bugs do not chew wood, wiring, drywall, or fabric. They do not breed inside, and they do not eat food in your kitchen. The problems they cause are about mess and numbers.

• Stains: Their droppings leave small red-orange spots on curtains, walls, and light-colored fabric.
• Smell: Crushed bugs give off a bad odor.
• Crowds: Hundreds may gather on siding, window frames, and doors.
• Indoor visitors: Some slip inside through gaps and wander toward windows.

Boxelder Bug Harm at a Glance

Concern	Risk level	What to expect
People	Very low	No stings or disease; bites are rare
Pets	Very low	Bad taste keeps most pets away
Plants and trees	Low	Minor spotting on leaves and seeds
House structure	None	They do not chew or tunnel
Curtains, walls, fabric	Moderate nuisance	Droppings can stain
Food and pantry	None	They do not feed indoors

Why Boxelder Bugs Invade Thurston County Homes in Fall

Boxelder bugs come to your house to survive the winter. Each September, adults leave their host trees and gather on warm, sunny walls that face south or west. As nights get colder, they crawl into cracks around windows, gaps under siding, attic vents, and wall voids.

Once inside the walls, they do not eat. According to WSU Entomology, they live off stored body fat until spring.

This habit of hiding for the winter is called overwintering, and boxelder bugs aren’t the only pest that does it. Like stink bugs that overwinter inside homes, they wait out the cold in wall voids and come back out when spring warms things up.

A few local factors make South Sound homes a target:

• Mild, wet winters with sunny breaks. Warm winter days can wake bugs up. You may see them on the sunny side of the house or near indoor windows in January or March.
• Lots of host trees. Maples are common across Thurston County, and many yards have planted boxelder trees.
• Light-colored houses. WSU notes that boxelder bugs are drawn to white homes.
• They travel. Boxelder bugs can fly up to 2 miles to find shelter, so your neighbor’s tree counts too.

How to Keep Boxelder Bugs Out This Fall

The best way to stop boxelder bugs is to block them before they gather. Here are the steps that work.

1. Seal cracks early. By early September, caulk gaps around windows, doors, siding, and where pipes or wires enter the house. The same work also keeps out other pests, like sealing gaps with steel wool and caulk to stop mice.
2. Weatherstrip doors. Add door sweeps and replace worn weatherstripping.
3. Screen vents. Cover attic, soffit, and crawl space vents with fine screen. Fix torn window screens.
4. Vacuum, don’t swat. Indoors, use a vacuum to pick up bugs. Empty the bag or canister into a sealed trash bag outside. Crushing them causes stains and smells.
5. Use soapy water outside. Spraying clusters with insecticidal soap or dish soap mixed with water kills them on contact.
6. Skip cutting down trees. Removing your boxelder tree will not stop bugs from flying in from nearby yards.
7. Time a perimeter treatment. A professional treatment on the foundation and siding works best in late summer, before bugs start to gather.

Want help finding and closing the gaps? Our exclusion and repair service seals the entry points boxelder bugs use. For more fall prep ideas, see our guide on how to keep bugs out this fall.

Related Questions to Explore

When to Call a Professional

A few boxelder bugs on the siding are normal in the fall. It is time to call a pro when:

• You find bugs inside your home every day.
• Hundreds gather on the same walls year after year.
• The gaps they use are high up, like rooflines, second-story windows, or attic vents.
• Droppings are staining your curtains, walls, or furniture.
• You are also seeing stink bugs, spiders, or rodents. That often points to the same open entry points.

Bigfoot Pest Management is a locally owned, family-run team serving Olympia, Lacey, Tumwater, Yelm, and the rest of the South Sound.

We use Integrated Pest Management (IPM), which means we find and seal how bugs get in first, then treat only where it is needed.

Our pest prevention plans include perimeter treatments timed before the fall rush, and if the pests come back, so do we. We are licensed by the Washington State Department of Agriculture (License #84786).

Conclusion

Boxelder bugs look alarming in big groups, but they are a nuisance, not a danger.

• They do not sting, spread disease, or damage your home’s structure.
• The real problems are stains, smells, and bugs wandering inside.
• Sealing gaps early and timing a perimeter treatment in late summer are the best ways to keep them out.

If boxelder bugs have taken over your siding this fall, we can help. Contact BigFoot Pest Management or get a quote for your Olympia pest control needs today.