Box Elder Bugs on Your House? Here’s Why and How to Get Rid of Them

Box elder bugs cover sunny walls every fall because they are looking for a warm, protected place to spend the winter, and the gaps in your siding are the closest thing they can find. They are a nuisance rather than a threat, and the most effective control happens before they ever get inside.

Box elder bug calls start every September across Wisconsin, Iowa, Nebraska, and South Dakota. A homeowner notices hundreds of black and red insects clustered on the south side of the house, crawling around window frames and lining the edge of the garage door, and by October a few are wandering across the living room. These bugs do not chew wood, they do not breed inside your home, and they very rarely bite. The frustrating part is that once they are tucked into the walls there is little you can do except wait them out, which is why the timing of everything below is so important.

How to Identify a Box Elder Bug

Adult box elder bugs (Boisea trivittata), also spelled boxelder bugs, are about half an inch long with a flat, elongated black body. Three red-orange stripes run lengthwise down the section just behind the head, and the edges of the wings are outlined in the same red-orange color. Younger bugs, called nymphs, are smaller and mostly bright red, and in late summer you will often see both stages mixed together in the same cluster.

They are easy to confuse with a couple of other insects that show up on homes at the same time of year. Asian lady beetles and stink bugs follow the same fall pattern of gathering on warm walls, and the quickest way to tell them apart is by shape and by what happens when you disturb them.

• Box elder bugs are flat, black, and about half an inch long, with red-orange stripes and wing edges. Their droppings leave reddish spots, and they smell when crushed.
• Asian lady beetles are round, dome-shaped, and orange to red, with a variable number of spots and a white M-shaped mark behind the head. They release a yellow fluid that stains and smells, and they can give a small pinch.
• Brown marmorated stink bugs are shield-shaped and mottled brown, with light bands on the antennae, and they give off a strong odor when handled or crushed.

If what you are seeing is round and orange, our posts on why Asian beetles look like ladybugs and how to get rid of Asian lady beetles cover that pest in detail. For brown, shield-shaped bugs, see our guide to getting rid of stink bugs in the home.

Why Box Elder Bugs Gather on Your House in the Fall

Through spring and summer, box elder bugs live in trees, using their straw-like mouthparts to feed on seeds and sap. Their favorite food is the seed of the female box elder tree, a fast-growing member of the maple family that is common in yards, along creeks and in windbreaks throughout the region. They will also feed on the seeds of other maples and, to a lesser degree, ash trees.

When the nights cool off in late summer, the adults stop feeding and begin searching for somewhere to overwinter. In the wild, that might be a crack in tree bark or a layer of leaf litter. Your house offers something much better, with walls that soak up the afternoon sun and a network of gaps behind siding, trim and soffits. The bugs gather in the warmest spots first, which is why the south and west walls of a home are often covered while the north side is nearly bare. Box elder bugs are also drawn to groups of their own kind, so a small cluster in September can grow quickly over the following weeks.

Why Am I Seeing Box Elder Bugs Inside in Winter or Spring?

The bugs that make it into your walls in the fall spend the winter in a dormant state. On a sunny winter afternoon, or once temperatures start climbing in March and April, the warmth wakes them up. Some find their way back outside, but many follow the heat inward and come out around outlets, light fixtures, baseboards and window frames. These are not new bugs hatching indoors. They are the same adults that moved in months earlier, and they cannot reproduce until they return to the trees in spring.

Are Box Elder Bugs Harmful?

For people and pets, no. Box elder bugs do not carry disease, they do not get into stored food, and they do not damage wood, drywall or insulation. Their mouthparts are built for piercing seeds, and while they can occasionally poke the skin when handled, it is uncommon and usually leaves nothing more than a small red mark.

The problems they cause are mostly cosmetic. Their droppings leave small reddish-orange spots that can stain curtains, light-colored walls and upholstery. Crushing them makes things worse, since it smears a stain and releases an unpleasant smell, which is why swatting them with a shoe or paper towel is one of the least effective ways to deal with them indoors.

Do Box Elder Bugs Damage Trees or Plants?

Not in any meaningful way. Heavy feeding can leave some leaves spotted or slightly distorted, but box elder bugs do not kill trees or cause lasting harm to landscaping. They will sometimes feed on soft fruit such as apples, plums or grapes and leave small dimpled spots behind, and that is about the extent of the damage.

How to Get Rid of Box Elder Bugs Inside Your Home

Once box elder bugs are in your living space, a vacuum is the best tool you have. It removes them without staining surfaces and keeps the smell contained, as long as you empty the canister or remove the bag right away and seal it before throwing it out. A shop vac works well when larger numbers collect near windows or in a sunroom.

Spraying insecticide indoors accomplishes very little. The bugs you see are a small fraction of the ones sitting in the wall voids, and household sprays cannot reach them there. Killing large numbers inside the walls can also leave behind a supply of dead insects that attracts carpet beetles. Rather than chasing individual bugs, pay attention to where they keep appearing, whether that is a particular window, a ceiling light or an outlet, and seal those gaps from the inside to cut down on how many make it into the room.

How to Keep Box Elder Bugs From Getting In

Prevention outside the house is where you can make the biggest difference, and it depends on getting the timing right. The work should be done by late summer, ideally in August or early September, before the bugs start gathering. Once clusters are covering your siding in October, many have already worked their way into the walls.

Start with a walk around the outside of your home, paying the closest attention to the south and west sides. Look for these common entry points:

• Gaps around window and door frames, which can be sealed with a quality silicone or acrylic latex caulk
• Torn window screens and screens that do not sit flush in their frames
• Worn or missing door sweeps and weatherstripping, including along the garage door
• Openings where cables, utility lines, dryer vents and outdoor faucets pass through the siding
• Gaps under fascia boards and soffits, along with unscreened attic or roof vents

Sealing every crack is not realistic on most homes, especially older ones, but closing the larger openings on the sunny sides of the house will noticeably reduce how many bugs end up inside. For a wider look at getting your home ready for the colder months, read our post on why pest control is essential in fall.

Does Soapy Water Kill Box Elder Bugs?

It does, on contact. A spray bottle or garden sprayer filled with water and a generous amount of liquid dish soap will kill the bugs it hits, and it works well on clusters sitting on siding, foundation walls and decks. It has no lasting effect, though, so it only helps with the bugs in front of you and has to be reapplied as new ones arrive. If you are spraying painted surfaces, test a small area first.

Should I Cut Down My Box Elder Tree?

Removing a female box elder tree can reduce the number of bugs around your home, but it rarely solves the problem by itself. Box elder bugs are capable fliers and will travel from trees on neighboring properties, which is why homes without a single box elder in the yard still get them. Only female trees produce the seeds the bugs depend on, so male trees play a much smaller role. If a tree is already coming down for other reasons, its removal may help, but it is not worth taking out a healthy shade tree for this alone.

When to Call a Professional for Box Elder Bugs

If box elder bugs return in large numbers every year despite sealing and spraying, a professional perimeter treatment is the most reliable fix. A licensed technician applies a residual product to the exterior walls, eaves and entry points where the bugs gather, timed for late summer and early fall so it is in place before they go looking for shelter. Because the treatment stays active for weeks, it keeps working as new waves of bugs land on the house, which is something soapy water cannot do.

At Fenix Pest Control, we handle box elder bugs as part of our residential pest control service, pairing exterior treatments with an inspection of the entry points that let them in. If you are already seeing clusters on your siding this fall, it is not too late to treat the outside of the house and cut down on how many show up indoors this winter. You can learn more on our box elder bug pest library page, or send us a message through the form below and a Fenix rep will be in touch within minutes.

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