Are Banded Alder Borers Dangerous to Humans? Assessing Risks to Human Safety

The banded alder borer (Rosalia funebris) is a strikingly beautiful beetle native to the Pacific Northwest.

Often found on alder, ash, and California laurel trees, these insects flaunt their vibrant white-blue and black coloration from March to August [1].

Although they may look intimidating, banded alder borers are not considered dangerous to humans. These beetles focus primarily on feeding and reproducing in hardwood trees [1].

Are Banded Alder Borers Dangerous to Humans?

The real concern related to beetles in the United States is the emerald ash borer (Agrilus planipennis), an invasive species responsible for the destruction of tens of millions of ash trees across 30 states.

Unlike the banded alder borer, the emerald ash borer can drastically impact community landscapes and forests [2].

Interaction With Humans: Are They Dangerous?

Banded Alder Borers, despite their intriguing life cycle and striking appearance, are not dangerous to humans.

These longhorn beetles primarily feed on decaying wood and have no interest in human activities. They neither bite nor sting, and they do not carry any diseases that can pose a threat to human health.

Banded Alder Borer Overview

Classification

The Banded Alder Borer (Rosalia funebris) belongs to the Cerambycidae family, commonly known as longhorn beetles. These beetles are characterized by their long antennae, which are often longer than their bodies.

Identification

Distinct features of Banded Alder Borers include:

  • Black and white coloration
  • Long antennae
  • White-blue bands across their bodies

For a better understanding, let’s compare Banded Alder Borer with another longhorn beetle:

FeatureBanded Alder BorerOther Longhorn Beetle
ColorationBlack and WhiteVarious
Antennae LengthLong (often longer than their bodies)Varies
MarkingsWhite-blue bandsVaries

The Banded Alder Borer’s striking appearance, featuring black and white-blue bands, sets it apart from other longhorn beetles.

Banded Alder Borer

Remember, if you ever encounter these beetles, it’s essential to be cautious and avoid handling them without appropriate knowledge and equipment.

Life Cycle and Habitats

Banded Alder Borers undergo four distinct life stages: egg, larva, pupa, and adult. From April to August, adult beetles emerge and engage in mating activities.

During this period, female beetles lay their eggs one by one on small to medium-sized branches that are either dying or recently deceased.

Eggs and Larvae

Banded alder borers (Rosalia funebris) lay eggs on various hardwood trees, such as alder, ash, willow, oak, California laurel, and maple. They particularly target trees with rot and access to water.

The following are some key features of banded alder borers’ eggs and larvae:

  • Eggs: Usually laid in groups on the tree’s bark
  • Larvae: Bore into the tree, feeding on the inner wood and creating tunnels

Pupa and Adult

Banded alder borers have a unique pupal stage and adult phase:

  • Pupa: The larva metamorphoses into the adult insect within a protective cocoon
  • Adult: Banded pattern, black and white or blueish-gray, with long antennae

Comparison of life stages:

Life StageCharacteristicsDuration
EggLaid in groups on tree bark2-3 weeks
LarvaBore into wood, create tunnels6-7 months
PupaMetamorphosis within a cocoon2-4 weeks
AdultBlack and white/blueish-gray coloring, long antennae1-2 months

Identifying Potential Damage

Banded alder borers are not known to pose any direct harm to humans. However, their wood-boring behavior can sometimes cause structural damage in the affected trees.

Visible Signs of Infestation

One common visible sign of a banded alder borer infestation in trees is the presence of holes in the bark and wood. These holes are typically:

  • Small in size
  • Oval or round in shape

Another indication of an infestation is the presence of dead branches. These can result from the beetles’ larvae feeding on the tree’s heartwood, which can cause structural damage to the branches over time.

Impact on Trees

Banded alder borer beetles generally target alder, ash, and California laurel trees, occasionally attacking other hardwoods as well. The primary impact of these beetles on trees includes:

  • Damage to the heartwood and bark
  • Weakening or killing branches
Banded Alder Borer

However, healthy trees can usually recover from infestations, while weakened or stressed trees may be more susceptible to lasting damage.

Healthy vs. Stressed Tree

FeaturesHealthy TreesStressed Trees
ResistanceResilient to infestationsMore susceptible
RecoveryCan recover effectivelySlower recovery
DamageMinimal lasting damageMore extensive

Identifying potential damage caused by banded alder borer beetles is crucial, particularly for stressed or weakened trees.

Examining visible signs of infestations, such as holes and dead branches, can help detect these pests and take appropriate actions to protect the affected trees.

Impact on Home and Garden

The Banded alder borer infestations in firewood can be problematic, as they can enter homes and gardens in search of new host trees. This bug typically attacks stressed or declining trees in the U.S, Canada, and Mexico.

Banded Alder Borer

Preventing and Controlling Infestations

To keep BAB populations in check, there are various prevention and control measures:

  • Fresh paint: Applying fresh paint to trees can deter BAB from infesting them by masking natural scents that attract the beetles.
  • Vacuuming: Regularly cleaning up wood debris can help prevent the buildup of infested firewood and reduce the population in your garden.
  • Healthy trees: Maintaining tree health can reduce the risk of infestation, as BAB usually targets weaker or vulnerable trees.

Here’s an overview of the pros and cons of these methods:

MethodProsCons
Fresh paintProtects trees effectivelyMay require frequent reapplication
VacuumingRemoves debris easilyTime-consuming
Healthy treesMaintains overall tree healthMay require professional assistance

Conclusion

Despite its striking appearance, it is not dangerous to humans. These beetles primarily focus on feeding and reproducing in hardwood trees, and their impact on humans is minimal.

However, being vigilant for signs of infestations, especially in weakened trees, can help protect the affected trees and prevent further spread.

Footnotes

  1. https://entomology.oregonstate.edu/sites/agscid7/files/entomology/Banded_Alder%20Borer_13.pdf

Readers’ Mail

Over the years, whatsthatbug.com has received hundreds of letters and some interesting images asking us about banded alder borers. Scroll down to have a look at some of them.

Letter 1 – Banded Alder Borer

A beetle like insect with really long antennae.
Sat, Jul 4, 2009 at 7:20 PM
I have no idea what this bug is. It was so intriguing, however, I took about 40 pictures of it! I think it’s a beetle, since it can fly and its wings are hidden under a hard shell. It had black and white stripes.
Please identify this bug!
Grants Pass, Oregon

Banded Alder Borer
Banded Alder Borer

Your insect is a Banded Alder Borer, Rosalia funebris, which is sometimes called a California Laurel Borer, but according to Charles Hogue in Insects of the Los Angeles Basin “it does not use California laurel (Umbellaria species) as a primary host.” 

According to BugGuide, the  “Larvae feed in dead hardwood trees: maple, alder, oak, willow, etc.”  Some borer beetles attack living trees, but this is not the case with the Banded Alder Borer.

Banded Alder Borer

Letter 2 – Banded Alder Borer

Black and white bug
Location: Parksville, BC.
August 19, 2011 9:13 pm
Parksville, BC.
august 19 2011.
it is about an inch and a half long
thanks very much
Signature: anon125

Banded Alder Borer

Dear anon125
This beautiful creature is known as a Banded Alder Borer or California Laurel Borer,
Rosalia funebris, and BugGuide indicates is is found in the:  “Western United States plus British Columbia and Alaska.” 

The larvae are Flatheaded Borers in dead hardwood trees including maple, alder, oak, willow and other hardwoods according to BugGuide, and Charles Hogue in his book Insects of the Los Angeles basin also adds ash and eucalyptus.  The Banded Alder Borer is not considered to be a harmful species. 

The Washington State University Cooperative Extension webpage written by entomologist Arthur L. Antonelli adds:  “The adults usually are encountered singly in summer, but occasionally they are attracted in numbers to fresh paint.”  Hogue made a similar comment. 

A European relative known as the Blue Rosalia, Rosalia alpina, is considered an endangered species and it has been featured on the postage stamps of several European countries including this beautiful example of a German stamp from 1993.  We don’t believe the Banded Alder Borer has ever appeared on a stamp.

Blue Rosalia on a German Postage Stamp

Thanks very much
it was on fresh paint – elastomeric paint.

Letter 3 – Banded Alder Borer

I live in Southern California and encountered the most hideous insect I have ever seen.
Here’s a description:
Black with white covering entire body.
Length: 2-3″
Antennae: very long 2″minimum
It resembled a skeleton.
Had 4-6 legs.
Body seemed very hard.
Please advise
—Peter DiVincenzo

Dear Peter,
My original guess would have been a Eucalyptus Tree Borer (Phoracantha semipunctata) but the black and white coloring suggests a relative, the Banded Alder Borer (Rosalia funebris) instead.

This is a very attractive beetle with black and white striped antennae which are longer than the body. It feeds on alder, ash and other hardwood trees, occasionally boring into the wood of laurel, live oak and eucalyptus as well. Adults are sometimes attracted to the fumes of fresh paint.

Try these sites for a photo and more information.

http://www.news.cornell.edu/Chronicle/97/6.19.97/
beetle.html

http://www.uvm.edu/albeetle/bandedalderborer.html

Letter 4 – another Banded Alder Borer

Bug I.D.
Bugman,
Greetings. Eye-balled this 1.75″ long critter on the banks of Penn Cove on Whidbey Island in the north Puget Sound of western Washington.

Been looking all over the Internet, as probably most of your other correspondents have, to no avail. Your wisdom on the identity of this beautiful beetle would be graciously accepted and most appreciated.
Cheers,
NwShetz

Hi NwShetz,
This is our second Banded Alder Borer photo today.

Letter 5 – Another Banded Alder Borer

Subject: what’s this insect?
Location: downtown Chico, CA
July 13, 2012 1:09 pm
I took this photo outside of the B of A downtown in Chico, CA yesterday. 7-12-12. It seemed out of place, had mouth Pincers.
It was very hot on the concrete…stayed to the shade. Started to mobilize wings once, but didn’t fly.
Looks like a beautiful piece of art…my husband called it the ”tiger beetle”. Is it poisonous/bad for the environment here? What is it’s normal environment?
Signature: Elizabeth Devereaux

Banded Alder Borer

Hello Elizabeth,
Even though we just posted another photo of a Banded Alder Borer, we think it is such a beautiful beetle we are posting your photo as well. 

Larvae are borers in dead wood, but not processed or milled wood, so they are not considered harmful.  You can find additional information on this lovely Longhorned Borer Family member by reading what is posted on Bugguide.

Authors

    by
  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

    View all posts
  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

    View all posts

69 thoughts on “Are Banded Alder Borers Dangerous to Humans? Assessing Risks to Human Safety”

    • Hi Nikole,
      We are happy to learn we correctly identified your Banded Alder Borer based on your vivid description. Sadly, our readers never read your original email to us, so we are reproducing it below.

      Subject: A weird bug
      Location: Longview, Washington
      April 24, 2013 9:02 am
      I found a bug in my yard one day as I was leaving for work and was unable to catch a photo of it but it was about 1 1/2 inches to 2 inches round it had lots of antennas and wings and was black and white zebra striped and it kinda of looked like a lion fish. … Can you please let me know if you have any idea what these kind of bugs are? Sorry I have no photos. …
      Signature: Nikole Rodriguez

      Reply
    • Hi Nikole,
      We are happy to learn we correctly identified your Banded Alder Borer based on your vivid description. Sadly, our readers never read your original email to us, so we are reproducing it below.

      Subject: A weird bug
      Location: Longview, Washington
      April 24, 2013 9:02 am
      I found a bug in my yard one day as I was leaving for work and was unable to catch a photo of it but it was about 1 1/2 inches to 2 inches round it had lots of antennas and wings and was black and white zebra striped and it kinda of looked like a lion fish. … Can you please let me know if you have any idea what these kind of bugs are? Sorry I have no photos. …
      Signature: Nikole Rodriguez

      Reply
    • They have powerful mandibles, and they might bite if carelessly handled, but they are not poisonous nor are they venomous.

      Reply
  1. We just found one of these in some older logs in our field. We took pictures but can’t get them to post here.
    We live near Port Orchard, Wa.

    Reply
  2. Do they shoot stinky smells like a stink bug? We found one in the yard today and my son accidentally splashed water on it. It stuck its but up in the air like it was going to spray! haha

    Reply
  3. This is so interesting–I just found one on our freshly painted deck. I wonder why they are attracted to fresh paint? I saw that this could be true on Bug Guide, then Googled it for more info and found this thread. It’s so interesting as ours was also on freshly painted deck with elasomeric paint as well, as the first person posted. There must be a smell that they like?

    Reply
  4. I’ve lived on the same forested property for 25 years and never seen one. Some 6 weeks ago, I felled a dozen Doug Fir & Western Red Cedar. Today I found one of these (Banded Alder Borer) on my deck.
    As far as the “fresh paint” smell as an attractant: Fresh paint can smell remarkably similar to fresh-cut wood (especially cedar). Perhaps it gives off a similar chemical. I’m not sure that’s the answer, but that’s the truth.

    Reply
  5. I’ve lived on the same forested property for 25 years and never seen one. Some 6 weeks ago, I felled a dozen Doug Fir & Western Red Cedar. Today I found one of these (Banded Alder Borer) on my deck.
    As far as the “fresh paint” smell as an attractant: Fresh paint can smell remarkably similar to fresh-cut wood (especially cedar). Perhaps it gives off a similar chemical. I’m not sure that’s the answer, but that’s the truth.

    Reply
  6. I have such a beetle living in my firewood! Can’t wait to see him again. This time I will be ready with my camera

    Reply
  7. Very happy to come across this page. Quite some time ago, I will say roughly the summer of 2003 or 2004, my husband had painted the apartment complex we were managing in Nanaimo B.C. with elastomeric paint and the next day there were hundreds of these beetles all over the building and shrubs. I had never seen them before or since. This answered my question as to why they came out that time.

    Reply
  8. Wow, I just found one on the windshield of my car, late afternoon in St Helens OR today. I had never seen anything like it. Quite striking and beautiful.

    Reply
  9. Great to know what it is! I just found one in Campbell River, B.C.
    on Vancouver Island. I was surprised to hear British Columbia is part of their territory. I have lived here all my life and have never
    seen one before.

    Reply
  10. Great to know what it is! I just found one in Campbell River, B.C.
    on Vancouver Island. I was surprised to hear British Columbia is part of their territory. I have lived here all my life and have never
    seen one before.

    Reply
  11. first hint its a borer was the large amounts of sap dripping from a 10 in dia alder.
    Another alder same age next to it was also infested with them. Cut both trees
    down and just today discover another alder infested. This one very large,
    perhaps 40-60 years old. Again the sap drippings on the ground under the alder
    was first evidence of this critter being what its named after. However these
    are living alder, not dead. So must be different than what was described in
    above article. We’ve found a dead beetle (as described in article) near both
    trees. This location is North Kitsap County, west of Seattle, Washington.

    Reply
    • The adult beetle specimens are quite valuable to collectors. If I were you, I would rear as many as possible out of the wood and try marketing them on ebay. My bet is they will bring over $100 each.

      Reply
  12. first hint its a borer was the large amounts of sap dripping from a 10 in dia alder.
    Another alder same age next to it was also infested with them. Cut both trees
    down and just today discover another alder infested. This one very large,
    perhaps 40-60 years old. Again the sap drippings on the ground under the alder
    was first evidence of this critter being what its named after. However these
    are living alder, not dead. So must be different than what was described in
    above article. We’ve found a dead beetle (as described in article) near both
    trees. This location is North Kitsap County, west of Seattle, Washington.

    Reply
  13. I am in Tulsa, OK and I have one of these roaming outside my house. Smaller than that one put probably the size of two fingers.

    From a quick search, I’ve never heard of these as far this east as Oklahoma.

    Thoughts?

    Reply
  14. I am in Tulsa, OK and I have one of these roaming outside my house. Smaller than that one put probably the size of two fingers.

    From a quick search, I’ve never heard of these as far this east as Oklahoma.

    Thoughts?

    Reply
  15. My kids just came to me and said, ” Mom what’s this weird looking bug?” From my understanding they’re common in the west and I’m in the South. Lake Charles Louisiana specifically. So I would like to know are they common in my area?

    Reply
  16. Just had one on on my windshield in HOUSTON TX. I wouldn’t get out the car. I had my son come out and move it!!! I know it’s not suppose to be here in Houston but it is!!! I have pics also!

    Reply
  17. We do Appliance Refurberation/Recycling & found 1 that came out from under a Refrigerator on 7-29-2019 @ 8:15pm in N.E. Salem, Or.

    Reply
  18. Just saw one on the beach at Deception Pass State Park on the northern end of Whidbey Island, WA. Just wandering along the sand… I have great pics but don’t know how to post one here.

    Reply
  19. Have one in vegetable garden.
    We’re in Sonoma County, California. We have a few downed oak limbs and some old wood stacked. Spectacular!

    Reply
  20. Have one in vegetable garden.
    We’re in Sonoma County, California. We have a few downed oak limbs and some old wood stacked. Spectacular!

    Reply
  21. Just found one on Seattle WA on a blue tarp, what a interesting find. Two summers ago Antlions appeared in a brick planter in front of the house.I fed them a few ants and a few other insects they left after some te never returned.

    Reply

Leave a Comment