Western Boxelder Bug: All You Need to Know in a Nutshell

The western boxelder bug is a common household pest that you might encounter in your home or garden.

These small, black insects with red-orange markings can be a nuisance, especially during the fall when they tend to invade homes in search of warmth and shelter.

Despite their frustrating presence, the western boxelder bug is not harmful to humans or pets and doesn’t cause significant damage to homes or plants.

To deal with these bugs effectively, it’s essential to understand their life cycle, habits, and the measures you can take to control their population.

Knowing when they’re most active and the most effective ways to prevent infestations can save you from the stress that comes along with having these unwelcome guests in your home.

Throughout this article, we’ll provide you with all the information you need to know about western boxelder bugs, from their appearance and behavior to the best ways to manage and prevent infestations.

Stay tuned to get well-versed with these pesky insects and deal with them efficiently.

What Is Western Boxelder Bug?

The Western Boxelder Bug (Boisea rubrolineata) is an insect that can be commonly found in North America.

It has a distinctive appearance, with a black body and reddish-orange markings. You’ll notice their body consists of six legs and two antennae, along with red lines on their thorax.

These bugs primarily feed on boxelder trees, especially the seed-bearing type¹.

However, they have also been known to feed on the foliage of maple, ash, alfalfa, and potatoes, as well as attack fruits on apple, pear, cherry, peach, and plum trees².

Their life stages consist of eggs, nymphs, and adults³. Immature bugs, or nymphs, are bright orange-red until they are half grown, becoming more similar to the adult’s appearance as they grow⁴.

Here are some key features of the Western Boxelder Bug:

• Scientific name: Boisea Rubrolineata
• Body color: Black with reddish-orange markings
• Legs: Six
• Antennae: Two
• Distinctive red lines on the thorax

Keep in mind that while Western Boxelder Bugs may be a nuisance, they are considered harmless and usually do not cause significant damage to vegetation⁵.

Neither are they considered dangerous for humans, since their sucking mouthparts are not strong enough to bite or sting you.

However, it is essential to be aware of their presence and take appropriate steps to manage their population if necessary.

Life Cycle

The Egg Stage

In the spring, usually around April, western boxelder bugs lay their eggs on host trees, like boxelder and maple. The eggs are oval-shaped and have a reddish-brown color. Here’s what to know about the egg stage:

• Eggs typically hatch in 10-14 days
• They are laid in clusters on leaves and bark
• The bugs prefer seed-bearing boxelder trees

The Nymph Stage

After the eggs hatch, the young boxelder bugs emerge as nymphs. During this stage, these are some of their features:

• Nymphs are small, wingless, and bright red in color
• They pass through five development stages (instars) before becoming adults
• Nymphs feed on tree seeds and foliage

As the nymphs mature, they start to develop black markings and wings. This process usually takes a few months, leading to a new generation of adult boxelder bugs.

The Adult Stage

Adult western boxelder bugs have a distinct appearance:

• Black in color with red lines on their thorax
• Around 3/4 of an inch long
• Three red lines on their thorax and red lines along their wings’ edges

Once they reach the adult stage, they mate and produce the next generation of boxelder bugs. Adults are known to attack fruit on apple, pear, and other fruit trees.

They overwinter in sheltered areas like buildings and tree crevices, waiting for the next spring to start the cycle anew.

Feeding Habits and Feeding Damage

The western boxelder bug feeds primarily on the seed bearing type of boxelder trees. They also feed on other host trees like maple and ash.

You might observe these bugs feeding on leaves, flowers, and seed pods of their host trees. Besides this, they can attack fruit on apples, pears, cherries, peaches, and plums.

Using their piercing and sucking mouthparts, they extract plant fluids which can lead to distortion of newly developing leaves.

Severe infestations may even cause leaves to appear chlorotic (yellow). Moreover, the bugs may also cause damage to flowers, tender twigs, and seeds of boxelder trees.

When it comes to fruit damage, western boxelder bugs and stink bugs have some similarities.

They both cause dimples on fruit, leaving small dark depressions on the surface. This feeding damage can result in a hard pithy area under the fruit’s skin.

Infestation and Impact on Homes

Western boxelder bugs can become a nuisance pest in and around homes, especially when they swarm in large numbers.

They typically feed on the leaves, flowers, and seedpods of box elder trees, but may also be found on maple and ash trees.

Although they don’t cause significant damage to the trees, their population growth can lead to potential problems for homeowners.

During fall, these bugs often gather on the warm, sunny sides of buildings. They may enter homes through cracks, eaves, doors, windows, and window screens.

Once inside, they seek warm areas like attics, wall crevices, and sunny windowsills.

To prevent boxelder bugs from infesting your home, consider the following:

• Seal cracks and crevices around your home.
• Install door sweeps on exterior doors.
• Repair damaged window screens.

Keep in mind that while boxelder bugs are a nuisance, they don’t pose a direct threat to your home. They don’t bite or cause structural damage, but their presence can be unsightly and annoying.

Interestingly, these bugs may even attract dermestid beetles, which could cause more significant problems.

Dermestid beetles feed on organic materials like carpets, furniture, and clothing, leading to potential damage in your home. So, keeping boxelder bug populations in check can also help keep dermestid beetles at bay.

Prevention and Control of Boxelder Bugs

To prevent boxelder bugs from infesting your home, take a few simple steps. First, remove any boxelder trees near your house, especially seed-bearing ones. Bugs tend to congregate and feed on those trees.

Also, ensure your house is well sealed. Install screens on windows and doors, and use caulk to seal any cracks or crevices on walls.

Here’s a quick comparison of different control methods:

Method	Pros	Cons
Water spraying	Chemical-free, easy-to-use	Won’t kill bugs, temporary
Pesticides	Effective in killing bugs	May harm beneficial insects
Diatomaceous Earth	Natural, relatively safe	Ineffective when wet
Soap and water	Non-toxic, easy-to-use	Spotty coverage, temporary
Vacuuming	Chemical-free, removes bugs	May require repeated use

For managing existing infestations, consider the following options:

• Water spraying: Use a hose to spray bugs off your home’s exterior. They’ll likely return, but this can buy you some time.
• Pesticides: Apply insecticides, like malathion, as directed to infested areas. Always follow label guidelines to prevent harm to humans and pets.
• Diatomaceous Earth: Sprinkle food-grade diatomaceous earth around your home’s perimeter. It can dehydrate the bugs as they crawl over it. However, be aware that it loses effectiveness when wet.
• Soap and water: Mix a soapy water solution and spray it on bugs found inside your home. The soap disrupts their exoskeleton, killing them. This method is less effective on large infestations.
• Vacuuming: Use a vacuum cleaner to remove bugs from your home. Dispose of the vacuum bag to prevent their escape. You may need to vacuum repeatedly for significant infestations.

Don’t forget to monitor bug activity consistently. By staying proactive and vigilant in your prevention and control efforts, you can minimize the impact of boxelder bugs on your home and property.

Additional Information

The western boxelder bug (Boisea trivittata) is a species of bug commonly found throughout North America.

As a member of the Rhopalidae family, they are known for their distinctive physical characteristics, such as their foundation dimples and black legs.

They typically inhabit areas with a variety of foliage in the environment, including trees and bushes.

These bugs can be a nuisance pest during the autumn months, as they tend to gather on windowsills, walls, and fencing. They are attracted to warm, sunny spots and will often try to sneak into your home through small gaps and holes.

Some similarities can be found between western boxelder bugs and stink bugs or cicadas. For example, all of these insects are known for releasing a strong odor when crushed.

However, it’s important to note that unlike stink bugs, western boxelder bugs do not pose a significant threat to your home or plants.

As western boxelder bugs can be quite persistent during the fall, it’s essential to seal any potential entry points around your home.

Closing gaps in your windowsills or foundation is a useful measure to prevent an infestation. Ensuring your environment is clean and free of excess debris can also minimize the chance of attracting these bugs.

In conclusion, while western boxelder bugs can be an unwelcome pest, implementing simple preventative measures can help mitigate their presence.

By being aware of their physical characteristics and typical behavior patterns, you’ll have a better understanding of how to spot them and keep them at bay.

Conclusion

In conclusion, the western boxelder bug, Boisea rubrolineata, is a common yet mostly harmless insect found across North America.

Characterized by their distinctive black bodies with reddish-orange markings, these bugs are more of a nuisance than a threat, as they do not pose significant harm to humans, pets, or even the vegetation they inhabit.

Their life cycle, from eggs to nymphs to adults, revolves primarily around boxelder trees, but they can also be found on other foliage and fruit trees.

As the seasons change, particularly in the fall, these bugs often seek shelter in homes, leading to potential infestations.

While they don’t cause structural damage, their presence can be bothersome, and they may inadvertently attract other pests like dermestid beetles.

Prevention and control methods range from physical barriers like sealing cracks and using window screens to more active measures such as water spraying, pesticides, diatomaceous earth, soap and water solutions, and vacuuming.

Understanding the habits and life cycle of the western boxelder bug is key to managing their presence effectively.

By taking proactive steps to prevent infestations and responding promptly to any signs of these bugs, homeowners can maintain a comfortable and pest-free environment.

Remember, while western boxelder bugs may be persistent, they are manageable with the right knowledge and tools.

Footnotes

1. https://treefruit.wsu.edu/crop-protection/opm/western-boxelder-bug/ ↩

2. https://extension.oregonstate.edu/families-health/healthy-homes/box-elder-bugs-are-harmless-nuisance ↩

3. https://ipm.ucanr.edu/agriculture/pear/western-boxelder-bug/ ↩

4. https://ipm.ucanr.edu/PMG/PESTNOTES/pn74114.html ↩

5. https://extension.unh.edu/resource/boxelder-bug-fact-sheet ↩

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about western boxelder bugs. Scroll down to have a look at some of them.

Letter 1 – Western Boxelder Bug

Subject:  Whats that Bug ?
Geographic location of the bug:  Vancouver Washington
Date: 01/29/2019
Time: 01:52 PM EDT
Your letter to the bugman:  Hi,
I have had a most distressing time attempting to determine the identity of this bug. It is a six legged black beetle of some kind but I fail to find any matching species in all of my research on the matter. I would be very appreciative if you could let me know what you think.
Regards,
How you want your letter signed:  Charles Richardson

Dear Charles,
This is not a Beetle, but rather a True Bug, so that might have made your identification attempts more distressing.  It appears to be a Western Boxelder Bug, Boisea rubrolineata, and according to BugGuide:  “Particularly noticeable in fall (often invade homes in search of shelter to hibernate) and in spring (when they emerge).”  Boxelder Bugs often form aggregations with numerous individuals.

Daniel,
Thank you so much. I very much appreciate your response and reply. You guys are a godsend…
Best Regards,
Charles

Letter 2 – Western Boxelder Bug

Subject: What’s this bug?
Location: Northern California foothills
November 29, 2015 5:18 pm
I live in the California Gold Country, halfway between Sacramento and Reno, NV. The elevation here is about 2500 ft. We have been in a prolonged drought, but have recently had a little bit of rain. I have lived in my house for 3 years and never seen these bugs before. About a month ago when the night time temperatures got cooler these bugs appeared on the sunny side of my house. The seem to enjoy sunning themselves but also seem undeterred by temperatures at or slightly below freezing. They particularly gather on window screens and windows. They fly or they run quickly when approached. The are about 1/2 to 1 inch in length and they have some red on their underside. They are very active during the day and I don’t see them after dark. They don’t seem to be doing any damage but there are a growing number of them and I am a bit concerned about them getting into my house and causing a problem. I have seen a few on my neighbor’s house but they seem to prefer my yellow house that gets a lot of sun. Oddly, my cat and dog who typically will play or catch bugs leave these guys alone. Any idea about what they are and should I be concerned? Thanks so much for your assistance.
Signature: Barbara

Hi Barbara,
This is a Western Boxelder Bug, Boisea rubrolineata, and it is considered a benign creature though they are prone to forming large aggregations that can become a nuisance if they are plentiful or if they enter the home.  The behavior you describe is very common for the species.  When weather cools down, they will enter homes to hibernate, but they will not cause you or your home any damage.

Hi Daniel,
Thanks so much! Glad to know I can let them be without worrying that they are eating my home.  Have a wonderful day!
Barbara

Letter 3 – Western Boxelder Bug

what kind of bug is this?
December 23, 2009
I would like to find out what kind of bug we found in our back porch. It was found In oregon during September, by itself outside on a warm cloudy day. Specifically we are in the mid willamette Valey about 1 mile from Willamette River. We are in a rural area
Josh Hoffert
Independence, OR. Mid willamette Valley. 1 mile from the river.

Hi Josh,
This is a Western Boxelder Bug, Boisea rubrolineata, a benign creature that often forms large aggregations and enters homes to hibernate as cooler weather approaches.  It can become a nuisance if it gets too plentiful.

Letter 4 – Box Elder Bug nymph

mystery bug
We have these in numbers in the back yard and are not sure that they are. I was thinking it was a type of chinch bug but I have not been able to verify. If you could help I would appreciate it.
Thanks allot,
Rick

Hi Rick,
You have an immature or nymph stage Box Elder Bug. Both nymphs and adults congregate together in large aggregations often on Box Elder and Maple trees, but also on other deciduous trees. They are usually noticed in fall and warm winter day. They sometimes enter homes in great numbers.

Letter 5 – Box Elder Bug

what kind of beetle is this?
We have these around our home here in washington. we have never seen them before. do you know what they are? let us know and thanks for your help.
sheryl gafford

Hi Sheryl,
You don’t have beetles, but True Bugs, more specifically, Box Elder Bugs. They often get very plentiful and also enter homes to hibernate.

Letter 6 – Box Elder Bug

Re: Beetle ID
I was at a covered bridge in western oregon (Ritner Covered Bridge near Wren), and saw thousands of these beetle coming out of cracks in the wood. Can you please identify this beetle, and tell me if they are feeding on the Douglas fir wood used for the trusses?
Thanks,
Kevin M. Groom, P.E.

Hi Kevin,
This is not a beetle, but a Box Elder Bug. They form very large aggregations of thousands of insects. They were not feeding on the bridge, but more likely beginning to hibernate. Perhaps as cold weather began, they sought shelter, but emerged on a warm sunny day. They often enter peoples’ homes in search of a good hibernation site.

Letter 7 – Box Elder Bugs

what are these?
heres my question what are these bugs, we have
millions of them on our tree?

You have Box Elder Bugs.

Letter 8 – Box Elder Bug nymph

Attached is a picture of a bug we have found around the foundation of our home and around our concrete patio. We have many in various sizes. This one is about 3/8″ long. Most are smaller. Smaller ones seem to be redder in color. We live in the Madison, WI area.
John Plumb

Nice photo of a Boxelder Bug nymph John.

Letter 9 – black and red bug – Box Elder Bugs

I live in central Florida. I have a type of bug that doesn’t bite, or make nest, it only crawls, but there are thousands of them. I cut my lawn and the whole end of the house gets covered in them. They are up to about 1 inch long, mostly black with a dark red back and as they grow the red goes underneath. They have 6 leg’s, Is this enough information? I really want rid of them as my wife really has a hard time with crawling bugs. Thank you in advance for any help you can give me.

They sound like Box Elder Bugs which can be a real nuisance.

Sorry I guess my description needs a little work. There are no stripes, just a red spot that starts on the back then seems to just be around the edges. I am going to try to put 1 on paper then scan it.
Thank You, Doc
The scanner idea isn’t perfect, If you can’t get a better idea from this pic I’ll try another way. Thank you for your pateince, Doc.

Dear Doc,
Your scanner idea was great. You have squashed Box Elder Bugs, both a winged adult and several nymphs. These bugs are pests, often entering houses to hibernate. We have never been successful in advising our readers how to rid their yards of them. They often form dense aggregations with thousands of Box Elder Bugs, adults and nymphs, forming colonies.

Letter 10 – Wheel Bug at Boxelder Bug Buffet

Black bug hanging out with boxelder bugs
Dear Bugman,
I was taking pictures of some nice boxelder bugs when I noticed about 6 of these bugs “hanging out” with them.What are these? They are huge!! Thanks much,
Christine

Hi Christine,
We know from your subsequent email that you correctly identified your Wheel Bug. You must be the envy of everyone with a Boxelder Bug infestation as your ecosystem has provided a natural predator that will no doubt control the numbers of the Boxelders and keep the situation manageable.

Dear Bugman. Never mind! Figured it out from your web-page. This is a wheel-bug, right? Very cool bug!!!! I presume it is munching on the box-elder bug nymphs???
Christine

Letter 11 – Western Box-Elder Bug

Hello,
I have been looking for someone to help me find out what kind of bug we have, and how to possibly get rid of them (as in, what will eat them). For as long as I can remeber we have had these bugs in our yard, and never had a problem. Unfortounatly, they have multiplyed and an astounding rate this year, and whenever we walk out of the house, there is a small cloud of them that forms. They are harmless but annoying, and about 3/4 of an inch in length. When they fly, the top of the abdomen is a bright, blood red, and when crushed smell bad. If it is any help, we live in North-western Oregon.
please help!
Kasey

Hi Kasey,
The Western Box-Elder Bug, Boisea rubrulineata, can get very plentiful. It feeds on box-elder, ash, and maple. Occasionally large numbers will enter homes. We have never found a way for our readers to eliminate them.

Letter 12 – Western Boxelder Bugs

What is this Beetle in Vancouver, WA
April 6, 2010
My husband’s brother in Vancouver, WA had many of these beetles on the back of his house, on the windows, deck etc. I thought he’d appreciate my finding out what they are and if they should be concerned or happy. Thank you.
Just found your web site and it is wonderful!
…Annette
Vancouver, WA

Dear Annette,
These are not beetles, but rather, they are True Bugs, Western Boxelder Bugs to be exact.  The Western Boxelder Bug, Boisea rubrolineata, is found west of the Rocky Mountains.  According to BugGuide, they:  “Feed on a variety of mostly woody plant species, but Boxelder (Acer negundo), Silver maple (Acer saccharinum), and other maples (Acer spp.), as well as Golden Rain Tree (Koelreuteria spp.) are favorites. Ash (Fraxinus spp.) is listed as a common host in literature, but it is usually not a favorite. Flowers and young seeds are prefered, so female trees often support larger populations; however, they also feed from foliage, at sap that leaks from wounds on branches and trunks, and from seeds on the ground. They will sometimes feed on trees of the Rose Family (such as Malus, Pyrus and Prunus), and rarely they may cause some minor damage to commercial fruit crops. They are recorded to feed on plants as diverse as Grass, Alfalfa, and Potatoes. It is even common to see them gathered and sucking fluids from other substances such as discarded human food, or smashed insects such as Grasshoppers and particularly Roaches.”  Western Boxelder Bugs, and their relatives to the east, the Eastern Boxelder Bugs, Boisea trivittata, are not considered to be pest species, but they can become a nuisance when they are extremely plentiful.  Both species may seek shelter indoors when the weather turns cooler.

Letter 13 – Western Boxelder Bug

Subject: What’s that bug?
Location: Northeast California, USA
November 29, 2016 11:47 am
Theis big is found in Northeastern California, USA. They are about 1/2 to 3/4 inches in length. Brown/black in color with red-orange marking I got along their backs. They can fly but not far and as they fly the open wings reveal a red body.
They seem to emerge from areas at the bottom of the house walls and are most active on warm days – especially in the spring and early winter ( i.e. Times when we have cool nights and warm days). They seem to nest near the house foundation and are very active on warm days following cold evenings. They seem to find their way into the house around door frames and sliding patio entrances.
What are these bugs? Are they harmful to people, pets or property (i.e. Like termites).? If harmful, is there a ecological control protocol that could discourage these bugs from nesting around the house?
Signature: Trevor

Dear Trevor,
This is a Western Boxelder Bug, Boisea rubrolineata, and according to BugGuide:  “Particularly noticeable in fall (often invade homes in search of shelter to hibernate) and in spring (when they emerge).”  We apologize for the very tardy response, but as our automated response states, we have a small staff and we cannot answer all the mail we receive.  We are currently selecting postings to go live to our site when we are away for the holidays, so your submission will go live at the end of the month.

Letter 14 – Western Boxelder Bug

Subject: mystery bug
Location: Southern California
June 28, 2017 8:10 am
Hi. Please identify this bug for me. I think it is an actual bug (Hemiptera). Thanks.
Signature: lanny@herbwalks.com

Dear Lanny,
This is a Western Boxelder Bug and they are known to form large aggregations when conditions are favorable.

Thanks, Daniel. That was fast! I saw a pic of a boxelder bug on your site and thought it looked similar but we don’t have boxelders growing in this area. Does it feed or host on another Southern California plant?
Lanny Kaufer

Hi Lanny,
According to BugGuide they will feed on many species of maple as well as other trees:  “hosts: Acer grandifolium (Bigleaf Maple), A. negundo (Boxelder), A. saccharinum (Silver Maple), Koelreuteria paniculata (Goldenrain Tree), and Sapindus saponaria (Western Soapberry)  Flowers and young seeds are preferred, so female trees often support larger populations; may also feed on foliage, on sap seeping from wounds on branches/trunks, and on fallen seeds. They will sometimes feed on trees of the Rose Family (Malus, Pyrus, Prunus, etc.) and cause minor damage to commercial fruit (rarely). They are recorded to feed on plants as diverse as Grass, Alfalfa, and Potatoes. It is even common to see them gathered and sucking fluids from other substances such as discarded human food, smashed insects, etc.”

There are Bigleaf Maples in the creek where this one was seen so that would explain its presence.
Thanks again!
Lanny

Letter 15 – Bug of the Month November 2017: Western Boxelder Bug

Subject:  What is this bug?
Geographic location of the bug:  Lexington washington
Date: 10/31/2017
Time: 06:46 PM EDT
This bug has been found in my bedroom.  I have an air conditioner in my window so I think it’s getting in through the cracks.
It has a red belly and wings but haven’t seen it fly.
How you want your letter signed:  Carol

Dear Carol,
This is a Western Boxelder Bug, a species that frequently seeks shelter indoors.

Letter 16 – Western Boxelder Bug

Subject:  A lot of mating going on
Geographic location of the bug:  Wenatchee, Washington State USA
Date: 03/06/2018
Time: 03:20 PM EDT
Your letter to the bugman:  We have many of these bugs doing the “thing” in our backyard at the moment. We have seen them on occasion over the years but never so many all at once mating.
How you want your letter signed:  Kevin

Dear Kevin,
This is a Western Boxelder Bug, Boisea rubrolineata, and according to BugGuide:  “Particularly noticeable in fall (often invade homes in search of shelter to hibernate) and in spring (when they emerge).”