The cottonwood borer (Plectrodera scalator) is a type of longhorned beetle known for infesting trees like cottonwood, poplar, and willow. Adult cottonwood borers have a distinct black and white pattern and can grow up to 1.5 inches in length. Their larvae are large, white, and deeply segmented grubs that can reach nearly 2 inches when fully grown. These insects are known for causing damage to trees but are rarely a threat to humans.
The question often arises – is the cottonwood borer bite poisonous? In general, their bites are not known for being venomous or harmful to humans, as they mostly feed on tree bark and wood. Although they might look intimidating, these beetles are not typically considered dangerous to people.
However, if you come across a cottonwood borer, it’s best to avoid handling it unnecessarily. This is simply to prevent any possible minor injury from a defensive bite. Overall, there’s no need for panic, as these wood-boring insects pose no significant threat to human health.
Cottonwood Borer Overview
The Cottonwood Borer (Plectrodera scalator) is a large longhorn beetle that can grow up to 1.25 inches in length. It has a distinct black and white coloration and its antennae are as long, or sometimes even longer, than its body.
These beetles are primarily found in the U.S., mainly in North America, where they breed in the bases and roots of living cottonwood, poplars, and willows1.
The life cycle of the Cottonwood Borer consists of several stages:
- Eggs: Female beetles lay their eggs in August at the base of host plants2.
- Larvae: Cottonwood Borer larvae are legless roundheaded borers that can grow up to 1.5 inches long2. They bore into tree roots and cause damage.
- Pupa: In this stage, the larval form transforms into that of a mature adult.
- Adults: Adult beetles emerge and cause damage while feeding on young trees, but most of the damage comes from the larval stage1.
Damage to host trees:
- Larvae cause most of the damage by hollowing, partially severing, or girdling trees1.
- Adults feed on young trees, leading to additional damage1.
Comparison table of Cottonwood Borer and Asian Longhorn Beetle:
|Feature||Cottonwood Borer||Asian Longhorn Beetle|
|Size||Up to 1.25 inches3||Up to 1.5 inches4|
|Antennae length||As long as, or longer than, the body3||Longer than the body4|
|Coloration||Black and white3||Black and white4|
Host Trees and Damage
Infested Trees and Host Plants
Cottonwood borers are wood-boring beetles that primarily infest cottonwood, poplar, and willow trees. They can also be found in other tree species like birch.
Examples of host trees include:
- Cottonwood trees
Symptoms of Infestation
Infestations can cause various symptoms, including:
- Holes in the bark
- Reddish frass (insect waste) in bark crevices or near the tree base
- Girdled branches and twigs
- Dieback in the tree canopy
Damage to Trees and Property
Cottonwood borers can cause significant damage to host trees, especially young ones. They tunnel through the inner bark and may reach the tree’s root system. In severe infestations, larvae create girdling tunnels which can damage the tree’s vascular system, causing wilting or even death.
Below is a comparison of healthy and infested trees:
|Healthy Trees||Infested Trees|
|Intact bark||Holes in the bark|
|No frass||Reddish frass|
|Healthy branches||Girdled branches|
|Full tree canopy||Dieback in the canopy|
Some consequences of cottonwood borer infestations include:
- Damaged or dead trees
- Girdled tree trunks
- Wilted or discolored leaves
- Potential property damage from weakened trees falling
The cottonwood borer does not have venom or poison glands, and its bite is not considered dangerous or poisonous to humans. However, infested trees may suffer damage or even die, so it is essential to address infestations promptly.
Reproduction and Development
Mating and Egg-Laying
Cottonwood borers are large, robust long-horned beetles with black antennae as long or longer than the body (source). The mating process begins with male beetles searching for female beetles using their long antennae to locate them. After fertilization, female beetles lay eggs on or around the roots of host plants.
Some key features of cottonwood borer mating and egg-laying:
- Male and female beetles participate in fertilization
- Eggs are laid on or around plant roots
Development and Metamorphosis
Cottonwood borer larvae cause most of the damage by feeding on and hollowing out the roots and lower trunk of host trees, like cottonwood, poplars, and willows (source). As the larvae grow, they undergo metamorphosis, passing through several stages before reaching adulthood. They pupate within the tree, and adult cottonwood borers emerge through holes in the trunk or branches.
A comparison table between Asian longhorned beetle and cottonwood borer:
|Feature||Asian Longhorned Beetle||Cottonwood Borer|
|Size||0.8 – 1.4 inches||1.25 inches|
|Antennae size||1.5 – 2.5 times body||As long or longer than body|
|Tree damage location||Trunk & branches||Roots and lower trunk|
|Host trees||Maple, poplar, birch||Cottonwood, poplar, willow|
Characteristics of cottonwood borer development:
- Larvae feed on and hollow out tree roots
- Undergo several stages of metamorphosis
- Pupation occurs within the tree
- Adults emerge through holes in the trunk or branches
Prevention and Control
Monitoring and Identification
To prevent and control cottonwood borer infestations, it’s important to monitor and identify them. The cottonwood borer is a type of longhorn beetle that has black and white-striped patterns, black antennae, and a cylindrical body. They belong to the roundheaded borers group attacking host plants like cottonwoods and other trees. Some key identification features include:
- Striped pattern
- Black antennae
- Cylindrical body
You can monitor their presence by looking for signs such as sawdust and holes in the bark of the tree, as well as damaged leaf stems. Also, stay alert for their predators, such as birds and spiders, as an increase in their presence may indicate a cottonwood borer infestation.
In some cases, chemical control might be necessary to manage cottonwood borer populations. Insecticides can be effective when applied at the appropriate time, usually when adult insects lay eggs on the tree trunks. However, chemical control has its pros and cons:
- Can effectively reduce borer populations
- Protects trees from further damage
- Can be harmful to non-target species
- May lead to pesticide resistance in borers
Cultural and Physical Control
Cultural and physical control methods include maintaining tree health, proper pruning, and removing infested firewood. These approaches provide a more eco-friendly alternative to chemical control. Here are some tips:
- Maintain tree health: Keep trees well-watered and fertilized
- Prune properly: Remove dead and damaged branches
- Remove infested firewood: Dispose of infested wood to avoid spreading borers
In areas prone to high winds, such as the United States’ Rocky Mountains, planting windbreaks can also protect host plants from wind damage, reducing the risk of cottonwood borer infestations.
The cottonwood borer, scientifically known as Plectrodera scalator, is a large, long-horned beetle. Its larvae can cause significant damage to cottonwood, poplar, and willow trees.
Cottonwood borer bites are not known to be poisonous. If you are bitten, it’s essential to maintain a watchful eye for potential allergic reactions or infections. However, the chances of being bitten are relatively low.
- Cottonwood borers aren’t hazardous to humans.
- Bites are generally uncommon.
- These beetles can cause significant tree damage.
- If bitten, individuals might experience an allergic reaction or infection.
As a result, cottonwood borers pose primarily a risk to trees rather than to humans. It is critical to focus on preventing tree damage when dealing with these insects.
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 – Cottonwood Borer
large yellow bug with black spots and black feet it can fly.
July 19, 2009
I was outside on my balcony when I saw about eight of these things flying around then one landed on the building and I have no clue what it is.
The Cottonwood Borer, Plectrodera scalator is usually described as white with black markings. It is a beetle in the family Cerambycidae. We really love the narrative mystery mood of your photo. It is quite cinematic.
Letter 2 – Cottonwood Borer
My father found this big guy on a glass door, at his work, in downtown Kansas City, Missouri. According to him, it seemed to sit in the same spot for hours, giving him the opportunity to take a picture. I’ve tried all kinds of sites, looking for what this creepy bug could possibly be, when I stumbled upon your website! It was about 2 1/2 inches long, not including the monstrous antennas. We made the conclusion that it’s a beetle… but of course, we could be wrong. Can you help us?!
Kansas City, Missouri
Your beautiful beetle is a Cottonwood Borer, Plectrodera scalator.
Letter 3 – Cottonwood Borer
BIG BUG in Texas
Sun, Jun 28, 2009 at 8:26 AM
I opened my front door to my upstairs apt. to leave, and walking in very relaxed like, was this neat looking creature. Naturally, I freaked and shut the door, then remembered how slow and feeble it seemed. As if it pretty much just wanted to get in out of the heat! it’s 102’F outside right now. So i put the broom and jar down on the floor and he mozzeied right on into it….like, dum de dum de dum…. but he doesn’t seem to like the jar too much, and i would like to find out whether or not this lil guy can hurt me? what does he need to survive? Cause he obviously, doesn’t like the heat! Btw- it’s a real light brown, almost cream/khaki in color underneath all the spots top of back and belly.
Biggest Bug I’ve seen in Texas
Fort Worth, TX
Your beetle is a Cottonwood Borer, Plectrodera scalator , one of the most beautiful North American beetles. According to BugGuide: “Adults are reported to browse on shoots of host trees, especially leaf-stems (petioles), and bark.” The host tree is the cottonwood. The beetle will not harm you, though they do have strong jaws and it might pinch slightly if it tries to bite you. We would urge you to release your captive.
i put him in box with coal rocks (those red ones that are very porous) and a variety of leaves/grass and tiny dish of water next to the rocks so that he could drink… i don’t know for sure, but it appeared to of eaten one of the leaves.
He took a nap that day and when i heard him crawling around again i took him back outside and he crawled right onto the little bush like tree and posed for the most beautiful picture! Unfortunally my memory is the only picture i will ever have of that as i did not have my camera/phone on me.
Letter 4 – Cottonwood Borer
black with checkers and has wings 1.5 inches long
July 16, 2009
Found this bug hanging around the hangar. What is it?
Sorry I don’t want a letter just curious as to the bug is. Thanks
This beautiful beetle is a Cottonwood Borer. Most of our reports come from Oklahoma and Texas.
Letter 5 – Cottonwood Borer
BIG BLACK AND WHITE BUG
July 31, 2009
I wrote yesterday, but have not received a copy of my email, so thought it did not go through. This bug was about 2″ long. It was thick with dark black legs and feelers that were thick. Its back legs were tipped at the foot area with black and white like its body. I don’t remember if the other legs were. I didn’t see wings, but it disappeared quick suddenly when I brushed it into the leaves with the broom. I’ve never seen one before.
Your spectacular Longicorn Beetle is the Cottonwood Borer.
Letter 6 – Cottonwood Borer
July 7, 2010
I found this bug in my back yard and looked it up on your website. Using your recourses, I think I have correctly identified this insect but I think that my photos depict this insect better than the one demonstrated on your website.
If you agree, you’re more than welcome to use them.
North Texas, Euless
Your identification of the Cottonwood Borer, Plectrodera scalator, is correct. We are not certain which of the many photographs posted to our website you are comparing your images to, but the submissions from our readership run the gamut from totally blurry to finely focused and of high resolution. Since the beginning of our site migration last year about this time, we have offered a new feature of being able to enlarge the images posted to our site to a maximum of 800×550 ppi, and all previous images are much smaller files.
Letter 7 – Cottonwood Borer
Yellow Beetle with Black Spots?
Location: Amarillo, TX
August 5, 2010 8:12 pm
My 6 year old daughter found this big guy (about 2.25 inches long) in our back yard under out granny smith apple tree. We watched him for a little while and then i used a twig to help him into some of the higher branches of the tree so that my 4 year old son wouldn’t squish him. (ahh, little boys!) Can you tell us what this guy is?
Your insect is a Cottonwood Borer, Plectrodera scalator. BugGuide lists the range as: “Eastern and Central United States. In east, found north of Washington, DC.” but virtually all the reports we have received over the years have been from Texas and Oklahoma.
Letter 8 – Cottonwood Borer
Location: Guthrie, Oklahoma (North of OKC)
September 26, 2010 1:04 pm
Found this on the back porch behind a broom…dead.
Looks as though it might be a flying beetle.
Interesting pattern on it.
Signature: Bugz E
Dear Bugz E,
The corpse you found is that of a Cottonwood Borer, Plectrodera scalator, according to BugGuide. It is in our opinion the most distinctive beetle found in North America north of the Mexican border.
Letter 9 – Cottonwood Borer
Nasty looking bug
Location: Duson, Louisiana
May 24, 2011 8:52 am
Please help me identify this bug. I believe it is a Spotted Cucumber beetle. Found in Duson, Louisiana
The Spotted Cucumber Beetle is a tiny creature. This magnificent beetle is a Cottonwood Borer.
Letter 10 – Cottonwood Borer
what is this?
Location: texas around san antonio
May 28, 2011 2:24 am
I work at sonic in Texas and I keep finding them in the parking lot. I thought maybe it was a cottonwood borer but there are slight differences between mine and the borer and I don’t want it to possibly be dangerous. can you help?
You are quite correct that this is a Cottonwood Borer.