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 .
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 .
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 .
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
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.
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:
|Feature||Banded Alder Borer||Other Longhorn Beetle|
|Coloration||Black and White||Various|
|Antennae Length||Long (often longer than their bodies)||Varies|
The Banded Alder Borer’s striking appearance, featuring black and white-blue bands, sets it apart from other longhorn beetles.
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:
|Egg||Laid in groups on tree bark||2-3 weeks|
|Larva||Bore into wood, create tunnels||6-7 months|
|Pupa||Metamorphosis within a cocoon||2-4 weeks|
|Adult||Black and white/blueish-gray coloring, long antennae||1-2 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
However, healthy trees can usually recover from infestations, while weakened or stressed trees may be more susceptible to lasting damage.
Healthy vs. Stressed Tree
|Features||Healthy Trees||Stressed Trees|
|Resistance||Resilient to infestations||More susceptible|
|Recovery||Can recover effectively||Slower recovery|
|Damage||Minimal lasting damage||More 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.
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:
|Fresh paint||Protects trees effectively||May require frequent reapplication|
|Vacuuming||Removes debris easily||Time-consuming|
|Healthy trees||Maintains overall tree health||May require professional assistance|
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.
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
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.
Letter 2 – Banded Alder Borer
Black and white bug
Location: Parksville, BC.
August 19, 2011 9:13 pm
august 19 2011.
it is about an inch and a half long
thanks very much
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.
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.
Antennae: very long 2″minimum
It resembled a skeleton.
Had 4-6 legs.
Body seemed very hard.
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.
Letter 4 – another Banded Alder Borer
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.
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
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.