Boxelder Bug: What It Is, Why It's on Your House, and How to Keep It Out

What is a boxelder bug?

A boxelder bug is a black insect about 1/2 inch long. Most are 12 to 13 mm, dark brown to black, with three red lines on the shield behind the head and thin red edges on the wings. Its scientific name is Boisea trivittata. It feeds on the seeds of box elder trees and gathers by the hundreds on sunny walls in fall.

It is a true bug, not a beetle. True bugs belong to the order Hemiptera and carry a beak for sucking fluids. Boxelder bugs use theirs on plant juice. Its family, Rhopalidae, has the odd name of scentless plant bugs. Yet these bugs smell bad when crushed. When the wings fold, they cross to form an X on the back. Under them, the body is bright red.

Eastern or western boxelder bug?

North America has two boxelder bugs, and they look almost the same. The eastern boxelder bug (Boisea trivittata) lives across the eastern US and southern Canada. Penn State says its range runs west to Nevada. The western boxelder bug (Boisea rubrolineata) ranges from British Columbia to California. The US Forest Service says it reaches east to Nevada, Utah and Texas.

Its red bands are slightly narrower and paler. The western bug is also more of an orchard pest: the Forest Service says it can damage fruit trees, pistachios and almonds. Otherwise both species live the same way, and the steps below work on either one.

This matters when you read other pages. The University of California page that ranks near the top of many searches is written about the western bug. PestWorld, on the other hand, calls the boxelder bug native to the western US. It then describes the eastern range, which reads as if it has merged the two species. East of the Rockies, outside Texas, you almost certainly have the eastern one.

Boxelder bug or something else? Bugs that look like boxelder bugs

Check the shield behind the head first. A boxelder bug has three red lines running lengthwise on it. UC IPM says those lines separate it from the look-alikes it lists. Then check where you found it. Boxelder bugs crowd sunny walls in daylight. The one look-alike that matters for your health, the kissing bug, comes out at night.

Red-shouldered and small milkweed bug features from Colorado State University. Western boxelder bug and golden raintree host from the US Forest Service. Kissing bug features from Texas A&M. Bed bug, large milkweed bug and clover mite details from our own guides.

UC IPM also lists squash bugs, leaf-footed bugs and the bordered plant bug as common mix-ups. If yours is brown with flat, leaf-shaped flaps on its back legs, read our leaf-footed bug guide. Are the red bugs tiny specks that smear red when you touch them? Then they are probably clover mites, covered in our tiny red bugs guide.

Young boxelder bugs cause the bed bug scare. They are bright red, and finding one on a pillow makes people fear the worst. Bed bugs are flat, brown and wingless, and they hide in mattress seams. A red bug with black legs on a window is far more likely a young boxelder bug. If you do find flat brown bugs and blood spots, check our guide to what bed bugs look like.

Boxelder bug or kissing bug?

People search this pairing because both are black with red or orange marks. Look at the head and the outer edge of the body. Texas A&M says kissing bugs have a cone-shaped head, thin legs and coloured stripes around the edge of the body. They are about 1/2 to 1 inch long. A boxelder bug has a small head, and its red lines run along the back.

Behaviour helps too. Kissing bugs are mostly active at dusk and at night, according to Texas A&M, and they feed on blood. A boxelder bug basks in the sun with hundreds of others and feeds on seeds.

It is not a beetle

Many people call them box elder beetles, but they are true bugs. A beetle’s hard wing covers meet in a straight line down the back. A boxelder bug’s wings overlap in an X instead. Our black beetle identification guide explains the same check for other red-and-black insects.

Do boxelder bugs bite? Are they harmful?

Boxelder bugs do not bite people to feed, and they cannot sting. Their beak is made for plant juice. NPIC says there are rare reports of defensive biting. PestWorld adds that they can occasionally puncture skin when handled, leaving a small red spot like a mosquito bite. They carry no disease and do not damage the house.

So why do sources seem to disagree? Wisconsin Extension says they will not bite humans or pets, while Colorado State says they rarely bite. In practice both are right. A jab usually happens when a bug is handled or trapped, say inside a sleeve. That matches what people describe on Reddit. Wash the spot with soap and water.

If you woke up with bites, read our bug bite identification guide for the insects that do bite indoors. A photo of a bite cannot tell you which bug made it, so look for the insect.

Are boxelder bugs harmful to cats and dogs?

No. UC IPM says they do not injure people or pets, and Wisconsin says they will not bite pets. Their bodies carry bad-tasting chemicals, which is why few birds or other animals eat them. The real risk to pets is any spray you use. Keep them off treated walls for as long as the label says.

Why you should not squish a boxelder bug

Squashing one causes two problems. The crushed bug gives off a strong, unpleasant smell, and it can stain the surface it was on. Their droppings leave reddish-orange spots as well, and UC IPM says these spot curtains, furniture and clothing. Vacuum them, sweep them up or brush them into a jar instead.

What do boxelder bugs eat?

Boxelder bugs eat seeds. They suck juice mostly from the seeds, leaves and flowers of female box elder trees. Maple and ash come next. Some also feed on fruit, such as apples, plums, cherries, peaches, pears, grapes and strawberries. Inside your home they do not eat your food, your wood or your fabric.

The box elder tree (Acer negundo) is a kind of maple, and only the female trees grow seeds. That is why the University of Minnesota says the bugs are rarely found on male trees. They do little harm to the trees themselves. Penn State notes that feeding on new leaves can twist them or turn them yellow. Still, UC IPM says they do little damage to ornamental trees.

Fruit is where you may notice them. UC IPM lists apples, cherries, peaches, pears, plums and grapes among their foods, and the Forest Service adds strawberries. Wikipedia says the damage happens mostly in fall. It lists dimples, scars, misshapen fruit and early fruit drop on strawberries and some tree fruits. Even so, they are not a major farm pest. In a home garden, hosing them off the fruit is usually enough.

Indoors, they go looking for water. The University of Minnesota says they gather around houseplants for moisture. Wikipedia, citing Utah State, says they may feed on some houseplants too. So a boxelder bug on your plant pot is thirsty, not nesting.

Why are boxelder bugs on my house? What attracts them

Boxelder bugs come to your house for warmth and shelter, not food. In fall they look for a dry, protected place to spend the winter. Walls that face south or west catch the most sun. So they gather there first, then crawl into any gap they find. A seed-bearing box elder tree within a couple of miles adds to the numbers.

• A sunny wall. The University of Minnesota says they favour buildings with a lot of southern or western exposure.
• A tall or lonely building. Buildings taller than those around them, or alone on flat ground, also draw large numbers, says the same source.
• Gaps. Cracks around windows, doors, siding, pipes, vents, soffits and chimneys let them into the walls.
• A host tree nearby. Adults fly several blocks, says UC IPM, and up to 2 miles, says the University of Minnesota.
• Clutter by the foundation. Leaves, rocks, boards and weeds next to the walls give them places to hide.

The colour of your house probably does not matter. The University of Minnesota and Wisconsin Extension both say so plainly. Washington State University says the bugs are especially drawn to white houses. UC IPM also mentions light walls in winter sun. Our reading: the sunny wall is what draws them, and you simply notice dark bugs more on a pale one.

Boxelder bugs are not the only fall invader on a sunny wall. Asian lady beetles arrive at the same time and also stain and smell. Our ladybug vs Asian lady beetle guide shows how to tell those apart.

Why there are so many boxelder bugs this year

Numbers swing a lot from year to year. The University of Minnesota says they are most abundant during hot, dry summers that are followed by warm springs. Iowa State points to a very warm May and a dry July. In other years you barely see them. So one bad fall does not mean every fall will be bad.

People often blame a neighbour who cut down trees. University of Maryland Extension got exactly that question. Its answer: it is hard to say whether the tree work had any effect on where the bugs went.

Boxelder bugs in the house: are they breeding inside?

No. Boxelder bugs do not breed, lay eggs or feed inside homes. Every one you see indoors in winter or spring got in the previous fall, according to the University of Minnesota. They spent the cold months resting in your walls or attic. Then warmth from the sun or the furnace woke them. Once active indoors, they live only a few days.

That is why they seem to appear from nowhere on a warm day in January. Iowa State explains that bugs inside the walls stay still while they are cold. The ones warmed by the furnace or the sun crawl into the rooms. People in Saskatchewan describe the same thing on Reddit. A warm snap heats the wall cavity, and the bugs start moving.

There is no nest to find and destroy. They rest loose in wall gaps, behind siding and in attics, the way they would under bark or rocks outdoors. By spring the survivors try to get back outside. UMN notes that many stay trapped indoors, and UC IPM says trapped bugs eventually die.

Our rule of thumb, built from the extension biology above. No source sets a number for an infestation.

Boxelder bug life cycle: eggs, nymphs and adults

A boxelder bug goes through three stages, egg, nymph and adult, with no pupa. Eggs hatch in 10 to 14 days, the bright red nymphs molt five times, and new adults appear by midsummer. Most areas get two generations a year, and only adults survive the winter. Any nymphs still around in fall die at the first hard frost.

Sizes and hatching time from Penn State, the Forest Service and UMN. Egg colour from Penn State and UC IPM. Generations from Penn State and the US Forest Service.

In spring, the adults that survived winter fly to host trees and lay the first eggs. Their young grow up by midsummer and lay a second batch. The Forest Service says that second generation is usually the larger one. Cooler places may get only one generation, and Penn State says Pennsylvania gets one or two a year.

A baby boxelder bug, the nymph, is the bright red bug people find on tree trunks in early summer. It has wing pads but no working wings, so it cannot fly. With each molt it gets bigger and darker, until the last molt gives it full black wings with red edges.

How long does a boxelder bug live? It depends on when it hatched. Here is our reading of the life cycle. An adult from the late-summer generation lives through winter and lays eggs the next spring. So it can live most of a year. Once one wakes up inside your home, though, it lives only a few days to a week, says UMN.

When do boxelder bugs come out and go away?

Boxelder bugs leave their winter shelter from late April to early May in Pennsylvania. They fly back to host trees. You see crowds again from late August to October, when they gather on sunny walls. They go quiet after the first hard frosts, but some wake up and wander on warm winter days.

Typical months for the northern and central US. Sources: UMN, Penn State, Wisconsin, Colorado State and UC IPM. In warmer states the year runs earlier.

How to get rid of boxelder bugs

To get rid of boxelder bugs, vacuum the ones indoors and wash clusters off outside walls. Then seal the cracks and gaps they use before the end of August. Once they are inside your walls, nothing reaches them all, so keeping them out next fall is the real fix. Sprays come last, and outside only.

Start with what costs nothing. Once boxelder bugs are indoors, the only practical control is removing them by hand or vacuum, says UMN. Penn State calls sealing the house the best way to keep them out. And UC IPM says insecticide use is rarely justified.

1. Indoors: vacuum, do not spray

Inside the house, a vacuum beats any spray. Iowa State says household aerosol insecticides generally do not kill them, and most residual products are of little use. UC IPM goes further and says not to use sprays for boxelder bugs inside the house at all. During the worst weeks, vacuum every day or two. Empty the bag straight away, because Washington State University notes that a bag full of bugs soon stinks.

2. Outdoors: water first, then soap

Water is the cheapest tool you have. UC IPM says a forceful stream washes them off walls and tree trunks. NPIC notes they can be drowned, especially the young ones. Soapy water kills them on contact. Iowa State gives 5 tablespoons of liquid detergent per gallon of water. The US Forest Service gives the same amount, or 1/2 cup of dry laundry detergent per gallon.

Soap has limits, though. It only works on the bugs it wets, so you may have to spray daily while they keep arriving. University of Maryland Extension warns that soaps and oils can also kill helpful insects and damage leaves. The Forest Service says to keep the mix off foliage. Aim at the wall, not the garden.

3. Seal the house before the end of August

Sealing is the only step that changes next year. Boxelder bugs start hunting for a winter home in late summer. So the University of Minnesota says to finish repairs before the end of August. Check every place where two materials meet, such as brick and wood siding. Then check every spot where a pipe, wire, faucet or dryer vent goes through the wall.

Penn State recommends a good silicone or silicone-latex caulk. For larger gaps, UMN suggests expanding foam or copper mesh. Two cautions apply. Leave the weep holes at the bottom of brick and stone walls open, or fit vent plugs made for them, as UMN advises. Cornell warns that blocking airflow can cause moisture problems. And older houses with vinyl siding may never seal completely, says UMN, so expect fewer bugs rather than none.

If you rent, outside repairs are often the landlord’s job, so ask before you caulk or change screens. Old windows are a common way in. As one Reddit user put it, even closed, the bugs crawl in between the frames.

4. Should you cut down the box elder tree?

Maybe, but not first. UC IPM calls removing female box elder trees the most effective control. The University of Minnesota says it is not a good way to manage them, because adults fly up to 2 miles. Both have a point: removing your own tree helps only if it is the main source nearby.

If you plan new trees, choose something other than a box elder, as Wisconsin suggests. The Forest Service mentions seedless box elder varieties such as ‘Baron’ that attract fewer bugs. NPIC adds that male trees, which make no seeds, can replace female ones. A cheaper step is to sweep up the seeds under any female tree, which UC IPM also recommends.

5. Insecticides: outside, late summer, and last

If sealing and cleaning work, you do not need an insecticide. It makes sense only for a house that gets a heavy invasion every year. The University of Minnesota says the time to spray is late summer and early fall. That is when the bugs first cluster on the outside walls. Penn State advises having a licensed pest control operator apply a pyrethroid just before they gather.

Know the limits before you pay for it. Penn State says sunlight breaks these products down, so they may stop killing bugs after several days to a week. The Forest Service notes that boxelder bugs have built up resistance to many insecticides. UMN lists the active ingredients sold to the public as bifenthrin, cyfluthrin, deltamethrin, lambda-cyhalothrin and permethrin. Check that the label allows use on the outside of buildings.

UC IPM adds one more rule: keep spray from running off walls into storm drains. Those drains lead straight to creeks and rivers.

Where the experts disagree

Extension services agree on most of this. But not on everything. They differ on four questions. Do boxelder bugs bite? Should you cut down the tree? Does house colour matter, and is spraying the tree worth it? Here is each side and our reading of the evidence, so you can decide for your own home.

Our reading weighs how direct each source’s evidence is. None of these questions has a controlled study behind it.

What does not work

Several popular fixes do little, and one makes things worse. Bug bombs, dust inside the walls, diatomaceous earth around the house, spring spraying and scent repellents all get recommended online. Here is what extension entomologists actually say about each one.

• Myth 1

  “A bug bomb will clear them out.”

  Truth: It does not last. Penn State says foggers kill the bugs on walls and ceilings, but more come out of the walls soon after. A Michigan State entomologist answering on Ask Extension says total-release bombs are not recommended for them.

• Myth 2

  “Spray or dust inside the walls to kill them at the source.”

  Truth: Penn State advises against it. Dead bugs left in the wall can feed carpet beetles. The beetles then move on to wool, stored dry goods and other natural products in the house.

• Myth 3

  “There is a nest somewhere that needs destroying.”

  Truth: There is no nest. UC IPM, Penn State and the University of Minnesota all say boxelder bugs do not breed indoors. They rest loose in wall gaps and attics until spring.

• Myth 4

  “Diatomaceous earth around the foundation will stop them.”

  Truth: Probably not. The same Michigan State entomologist expects it to have little effect.

• Myth 5

  “Spraying in spring prevents next year's invasion.”

  Truth: It does not. The University of Minnesota says the spring bugs are leaving. Treating them has no effect on how many arrive the next fall.

• Myth 6

  “Cutting down the tree solves it for good.”

  Truth: It can help. But adults fly long distances, say the University of Minnesota and Wisconsin, so a tree down the street can keep supplying them.

• Myth 7

  “A scent such as peppermint or vinegar keeps them away.”

  Truth: We found no extension source that recommends any repellent. People on Reddit who tried scents report that nothing repels them.

Are boxelder bugs good for anything?

A little. Boxelder bugs are a native North American insect that feeds on tree seeds. They do the trees no real harm. They are not pollinators, and few animals eat them, because their bodies carry bad-tasting chemicals. Wikipedia notes that spiders are minor predators and that no major diseases or parasites affect them.

Chris Helzer is a Nature Conservancy scientist who writes the Prairie Ecologist blog. He argues that their bright orange-red markings warn predators off, which may explain why they can gather so openly. Our reading: the colouring that looks alarming on your wall is a message to predators, not a threat to you.

When to call someone

Most boxelder bug problems are a do-it-yourself job. Call a licensed pest professional if thousands come back every fall despite sealing. The same goes for walls too high to reach safely, or if you want an exterior treatment applied. If you rent and the gaps are in the building, call your landlord instead.

• A pest professional for heavy yearly invasions or high walls. Iowa State notes that professionals can use products not sold to homeowners.
• A contractor or handyman for gaps in soffits, fascia, siding or old windows that you cannot reach or fix.
• Your landlord for outside repairs, screens and vents in a rental.
• An arborist if you decide to remove a large female box elder tree.
• Your state extension office if you are unsure what the bug is, especially a possible kissing bug.
• A doctor if a bite mark spreads, swells or worsens, or if you think a kissing bug bit you.

Not sure what you have at all? Take a sharp photo from above and run it through our bug identifier by picture. For other bugs on sunny walls and sills, the free insect identifier works the same way.

Pest control disclaimer. Photo-based identification can help, but it is not always perfect. For dangerous spiders, large infestations, or anything you are unsure about, contact a licensed pest control professional.