Cottonwood Borer: All You Need to Know for Healthy Trees

The Cottonwood Borer is a large black and white longhorn beetle that can grow up to nearly 2 inches in length. Known to primarily infest cottonwood trees, these pests also target poplars and willows, causing significant damage to their hosts. Female Cottonwood Borers lay their eggs at the base of these trees in August, and the larvae bore into the tree as they grow.

As the larvae mature, they tunnel around the crown and buttress roots of the tree, creating galleries at and below the soil line. These tunnels can range from 2 to 3-inch diameter oval areas to 8 inches in length, depending on the tree’s size and infestation site. The damage caused by these pests can be detrimental to young trees, as their bark can be hollowed, partially severed, or girdled at or slightly below the root collar.

It’s essential to identify and manage Cottonwood Borer infestations early on, as they can cause irreversible damage to trees. Recognizing the signs of their presence and understanding their life cycle will help ensure the health and longevity of your cottonwood, poplar, or willow trees.

Cottonwood Borer Basics

Identification of Plectrodera Scalator

The Cottonwood Borer (Plectrodera scalator) is a type of longhorned beetle. It has a distinct black and white color pattern, measuring 1 1/4 to 1 1/2 inches in length. Notably, the larva is a large, white, deeply segmented grub, reaching 1 3/4 to 2 inches long when fully grown1. Here are the key features:

  • Color: Black and white
  • Adult size: 1 1/4 to 1 1/2 inches
  • Larva size: 1 3/4 to 2 inches

Distribution in the United States

Cottonwood Borers are found predominantly in the United States, infesting cottonwood, poplars, and willows2. Their larvae feed on tree trunks, causing damage, especially to young trees3.

Below is a comparison table of the trees cottonwood borer targets:

Tree Type Susceptibility to Cottonwood Borer
Cottonwood High
Poplars High
Willows High

Physical Characteristics

Distinguishing Adult Beetles

The Cottonwood Borer is a large longhorn beetle that measures about 1 1/4 to 1 1/2 inches in length. They have distinct coloration, featuring:

  • Black and white pattern on the body
  • Black antennae, as long or longer than the body
  • A robust appearance, with a large thorax

The black and white markings on their bodies are unique among longhorn beetles, making them easily recognizable. You can often find adult beetles on and around host plants during the summer.

Larvae and Pupae

Cottonwood Borer larvae are legless, roundheaded borers that grow up to 1.5 inches long. Their primary physical traits include:

  • Creamy white color
  • Deeply segmented body

Once the female lays eggs at the base of host plants, the larvae hatch and bore into the tree, causing most of the damage to the plant. During their pupal stage, they transform into adult beetles, eventually emerging to continue the life cycle.

Infestation and Damage

Host Trees and Damage Pattern

The Cottonwood Borer primarily targets cottonwood trees, but it also infests poplars and willows. Some common indicators of infestation include:

  • Larvae tunneling around the crown and buttress roots1
  • Galleries at and below the soil line, varying in length1

For example, a young cottonwood tree may showcase galleries that are 8 inches long, while an older or larger tree with an infestation site might display 2 to 3-inch diameter oval areas.

Impact on Tree Health

The health of the host trees might be impacted by the Cottonwood Borer in the following ways:

  • Adult feeding damages young trees2
  • Most damage is caused by larvae2
  • Young trees may be hollowed, partially severed, or girdled2

If a young tree experiences severe damage, it might break at or slightly below the root collar.

Life Cycle and Reproduction

Mating and Egg Laying

Cottonwood borers (Plectrodera scalator) are a species of longhorned beetles that infest cottonwood, poplars, and willows. Adults emerge from late May to early July and then begin mating. After fertilization, females oviposit, or lay eggs, in the bark crevices or soil near the base of host trees.

Larval Development

Once the eggs hatch, the larvae begin feeding on the tree’s inner bark and cambium layer, causing extensive damage known as girdling. During their development, the cottonwood borer larvae create galleries, which are tunnels they carve out within the tree or its roots.

Pupation and Adult Emergence

The cottonwood borer’s life cycle takes two years to complete. After a year of larval development, they pupate within their galleries in the second spring. New adults then chew their way out, leaving exit holes as they emerge.

Pros of cottonwood borers:

  • Some beetle collectors find them aesthetically appealing due to their large size and unique coloring.

Cons of cottonwood borers:

  • Cause significant damage to their host trees, potentially resulting in tree death.
  • Difficult to control, as they live within tree trunks and roots during most of their life cycle.

Comparison of two significant wood-boring insects:

Feature Cottonwood Borer Old House Borer
Order Coleoptera Coleoptera
Families Cerambycidae Cerambycidae
Host Trees Cottonwood, poplars, willows Primarily softwoods, e.g., pine, spruce
Damage Girdling, tree death Structural weakening of wood
Life Cycle 2 years 3-12 years

In summary, the cottonwood borer’s reproduction process involves mating, egg-laying by the females, larval development that lasts for about a year, and pupation in the second spring. The adult borers then emerge and leave exit holes in their host trees, marking the end of the life cycle.

Habits and Habitat

Preferred Conditions

The Cottonwood Borer (Plectrodera scalator) is a large, robust longhorn beetle belonging to the Cerambycidae family, commonly found in North America, particularly in the Great Plains and Rocky Mountain regions. They prefer sandy soils and are known to breed in the bases and roots of living trees like poplars, cottonwoods, and willows:

  • Poplar trees
  • Cottonwood trees
  • Willow trees

Sandy soils are especially favorable for the cottonwood borer’s habitat.

Expanding Range

The range of cottonwood borers has expanded over time due to several factors, such as climate change and the spread of host plants. These beetles can be found on and around their host plants during the summer, fulfilling their adult lifecycle responsibilities.

Seasonal Patterns

Cottonwood borers typically emerge around mid-May and can be seen during the warmer months of the year. They have a seasonality that affects their activity, and their predators, too, need to adapt and synchronize their behavioral patterns accordingly.

Throughout the cottonwood borer’s life, the majority of the damage is caused by its larval stage rather than the adult feeding stage. For instance, young trees can be hollowed, partially severed, or girdled at or slightly below the root collar, causing breakage and significant harm to the host plants.

Cottonwood Borers are an important aspect of North American ecology, and understanding their habits, habitat, and seasonal patterns provides us with valuable information to help manage their populations and protect our precious ecosystems.

Management and Control

Cultural Practices

Cultural practices can help prevent cottonwood borer infestation. These include:

  • Maintaining tree health: Proper cultivation, fertilization, watering, and thinning when necessary preserve high-value trees’ health1.
  • Eliminating debris: Removing infested, dead, or dying branches can reduce borer attraction and breeding opportunities1.

For example, in the U.S. South, cottonwood borers often cause destruction in nurseries, young plantations, and young natural stands on sandy soils2. Implementing healthy tree care and debris removal can mitigate their impact in these areas.

Chemical Treatments

Permethrin is a prevalent chemical treatment for managing cottonwood borer infestations3. However, it’s crucial to consider the pros and cons of using such treatments:

Pros:

  • Effectively kills the larvae and adult insects
  • Reduces the risk of further infestation

Cons:

  • Can harm beneficial insects and the environment
  • May not be suitable for all tree species or specific regions

Comparison of Cottonwood Borer and Ash Borer (Invasive Longhorned Beetles)

Feature Cottonwood Borer Ash Borer
Larval Stage Legless roundheaded borers, up to 1.5 inches long4 Larvae are cream-colored and flat, up to 1.2 inch
Host Trees Primarily cottonwood, but also poplars and willows5 Prefer ash trees
Infestation Effects Damage from larval tunneling, including hollowing, and girdling2 Damage by larval feeding, disrupting nutrient movement

In summary, managing and controlling cottonwood borer infestations requires a combination of cultural practices and chemical treatments. Remember to maintain tree health, remove debris and weigh the pros and cons of chemical treatments like permethrin.

Footnotes

  1. Oklahoma State University 2 3 4 5

  2. Texas A&M University 2 3 4 5 6

  3. University of Kentucky 2

  4. University of Kentucky

  5. Texas A&M University

Reader Emails

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

Letter 1 – 2011 Calendar Contender??? Cottonwood Borer

 

Cottonwood Borer?
May 27, 2010
Found this guy wandering about last night at a friend’s house. He’s has one heck of a grip & a serious set of mandibles. Is it in fact a cottonwood borer?
We’re located 50 miles south of New Orleans.
Lindsay
Southeastern Louisiana

Cottonwood Borer

Dear Lindsay,
You are absolutely correct.  This is a Cottonwood Borer, Plectrodera scalator.  This is one of the most beautiful images we have received this year.  Your photograph put a bug in our head to produce a 2011 What’s That Bug? calendar.  We last produced a calendar for 2006 in 2005.  That was quite a project, but with finishing the book, we wouldn’t mind a small visual publication.  Would you mind terribly Lindsay, if we wanted to use your image in a 2011 calendar?  Your photo is exactly what we love in an insect image:  that it not ever be included in a legitimate entomological text.  So dear readers, is a 2011 calendar something that you would like to see?  Please let us know by posting a comment to this announcement.

Letter 2 – Cottonwood Borer

 

Here’s a beauty for you.
Found this pretty beetle on the garden hose rack at my house. It was so big and bold. It is also a good model…..who sat for several pictures. Enjoy!
Pamela
League City, TX

Hi Pamela,
We have just spent the last two hours playing “catch-up” posting images that were sent yesterday, and we really need to do other things today. We could not resist the temptation to post just one more though. Your photo appeals to us on so many levels. The Cottonwood Borer, Plectrodera scalator, is truly a regal insect that is not easily confused with any other. We also love the fact that it was photographed on a garden hose. Our favorite photos tend to be the kind that would never find their way into legitimate entomological books because they are slightly quirky. Thanks for your beautiful submission of a beautiful beetle.

Letter 3 – Cottonwood Borer

 

Animal (unknown) 6-24-07 on deck railing
Hi, I’ve been looking at your website and find it most fascinating. Who knew there were so many kinds of bugs out there? Well, I guess ya’ll would…….LOL. Ok, my dad took these pics and e-mailed them to me and we have no clue what this thing is. I told him I’d check on the internet and try to find out. I found your website and have been enjoying it. Can you help? We live in central Arkansas. My parents’ house has lots of pine trees on one side and a variety of other trees and plants in the yard. Any help you can give would be most appreciated. Thank you
Yalonda

Hi Yalonda,
This is a Cottonwood Borer and most of our images come from Texas. It is nice to get a report from Arkansas.

Letter 4 – Cottonwood Borer

 

What is it?
Found this beetle crawling outside the house yesterday in Austin Texas. Thanks,
Bryan

Hi Bryan,
This large unforgetable beetle is a Cottonwood Borer.

Letter 5 – Cottonwood Borer

 

What is this bug???
This insect was found hanging out at our clinic’s back door. We are sure it didn’t have an appointment. Can you tell me what it is?
Michael J. Dolan
Junction City, KS

Hi Michael,
This is a Cottonwood Borer. Most of our reports come from Texas and it is nice to have a sighting of this gorgeous beetle from Kansas.

Letter 6 – Cottonwood Borer

 

a new pet?
In early July, we took this closeup of a bug in our Kansas backyard and then couldn’t find him (or his kin) again until today (9/6). This bug is about the size of a half dollar. The girls were so excited to see him again, they wanted to keep it as a pet! That is until all of a sudden we found out surprisingly that the bug has wings and flew away! What type of bug is this, and can we expect it to stick around?
Cindy

Hi Cincy,
Most of our reports of Cottonwood Borers come from Texas and Oklahoma. This distinctive looking beetle is not to be confused with any other in the U.S.

Letter 7 – Cottonwood Borer

 

Here’s a Cottonwood Borer from Albuqurque New Mexico
While at a horses how this guy visited our tent canopy in Albuquerque.
Randy

Hi Randy,
The stark white background in your photograph sets off the stunning pattern of this very distinctive Cottonwood Borer. It reminds us of a Richard Avedon photo.

Letter 8 – Cottonwood Borer

 

Cottonwood Borer?
Hello from Wichita, KS Is this a Cottonwood Borer? Thanks
Carrie

Hi Carrie,
You are correct. This is a Cottonwood Borer. Thanks for providing the interesting view of the underside as well as the more typical dorsal view.

Letter 9 – Cottonwood Borer

 

Not a Twig Girdler, but what??
Tue, Oct 21, 2008 at 11:35 AM
We live in Oklahoma in a mostly natural forrest of about 200 acres, creeks, bluffs and trees. This bug was on the patio as we were buildiing a cabinet. We have evidence of Twig Girdlers…branches cut off on the ground with green leaves still in tact. So I thought it may be one, but it did not have the distinctive markings a Girdler has. The tenacles are very long, and the length of the bug is about 2-3 inches and the mouth appears to be large enough to be used in biting or cutting. It is slightly more yellow than the picture shows with a definite black pattern. Any ideas?
skizi
Eastern Oklahoma

Cottonwood Borer
Cottonwood Borer

Hi skizi,
Your Longhorned Borer Beetle is a Cottonwood Borer, Plectrodera scalator.  Most of our photos of this spectacular beetle come from Texas and Oklahoma.

Letter 10 – Cottonwood Borer

 

long antennaed in apalachicola fl
Fri, Dec 5, 2008 at 8:47 AM
Good morning/afternoon, and thank you in advance,
What an amusing and informative site!
This August, we were walking the marsh trail at the NOAA interpretive center in Apalachicola Fl , and noticed this creature on the boardwalk rail…you can note the nailhead for scale. None of us are great photographers, so we got very close, and this little animal waved its antennae, turned around, walked back and forth a bit, giving us a few poses, then abruptly flew off, scaring the daylights out of the person whose nose was inches away. Do you know what this is? Thanks!!!
Lara
gulf coast Florida

Cottonwood Borer
Cottonwood Borer

Apalachicola cottonwood borer!
Fri, Dec 5, 2008 at 9:36 AM
Hello again!
If I had scrolled ALL the way down, I would’ve seen the strikingly similar bug that you identified as a Cottonwood Borer. At least now I think that’s what it is, after also cross-referencing other images with name! Hope you enjoy the pictures, at least…(sent earlier today) …this is a popular bug!
Thanks so much!
Lara
gulf coast FL

Cottonwood Borer
Cottonwood Borer

Hi Lara,
We are happy to see that you correctly identified your Cottonwood Borer with our website.  Your photos are a lovely addition to our archive, especially since this is the first Cottonwood Borer Beetle we have that was not sighted in Oklahoma or Texas.

Letter 11 – Cottonwood Borer

 

white & black beetle/grasshopper?
Sun, May 24, 2009 at 10:32 AM
we live in south louisiana….we have some very unusual bugs but this is 1 tops em……it was on my car…..it is black & white….it has a thorn on each side of its neck ….very long feelers…..the underneath of its legs look like hearts….please lemme know what yall think it could be…..it is pretty vicous,,,,
Layla Pinell
Montegut , Louisiana

Cottonwood Borer
Cottonwood Borer

Hi Layla,
This is a Cottonwood Borer, Plectrodera scalator, and there is little likelihood that it would be confused with any other insect since it is so distinctive.  BugGuide lists its range as “Eastern and Central United States. In east, found north of Washington, DC. (Apparently absent from Carolinas, Florida) ” typically near riverbanks and other places where its host trees willows and cottonwood grow.  Almost all of our reports have been from Oklahoma and Texas.

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.

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10 thoughts on “Cottonwood Borer: All You Need to Know for Healthy Trees”

  1. ….HAHA…WELL WE ARE @ THE BOTTOM OF THE BOOT & I HAVE SHOWN IT TO MANY PEOPLE & THEY HAVE NEVER SEEN 1….JUST YESTERDAY , ACTUALLY RIGHT AFTER I EMAILED YOU GUYS, MY HUSBAND YELLS FOR ME TO OUTSIDE…HE FOUND ANOTHER 1 BUT IT WASN’T BLACK & WHITE…BUT HAD THE SAME FEATURES BUT NOT THE SAME COLORS…..I DIDNT TAKE A PIC BUT I SHOULD HAVE……..

    Reply
    • Dear TJOswego,
      We like the calendar photos to have a very quirky aesthetic. Keep that in mind when you pull out the camera. Though it is quite lovely, your photo of a Clavate Tortoise Beetle is more suited to a traditional guide book.

      Reply
  2. You absolutely can use the picture. The reason for all of the bright colors is it’s on a class of 2010 plate since we were having a graduation party for my friend’s son. I’ve never seen these bugs down here before so it was too much of a great find to NOT snap a pic!

    Reply
    • Thanks Lindsay,
      We will have to look into the cost of this project before we seriously entertain publishing a calendar.

      Reply
  3. Would love to purchase a calendar, especially of photos like this one! Would make a great gift for kids in my daughter’s class – especially for hard to buy for boys!

    Reply
  4. Hi Bug Man

    I would like to see a bug calander (my godson would love it). Anyway……I am going to submit a really cool moth photo, as soon as I am done here. Thanks

    Reply
  5. We have just found a cottonwood borer on our cottonwood tree and my daughter deeply wants to keep it as a pet. Any tips on how to create a terrarium in which is could live happily?

    Reply

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