Are Locust Borers Dangerous to Humans? Uncovering the Truth

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Locust borers, scientifically known as Megacyllene robiniae, are a type of long-horned beetle that can wreak havoc on trees, particularly black locust trees.

While these insects can cause damage to plant life and may be a concern for arborists, it’s essential to determine if they pose a danger to humans as well.

Are Locust Borers Dangerous to Humans

Adult locust borers have distinctive yellow and black markings with a prominent “W” on their wing coverings.

This allows them to camouflage themselves on goldenrod plants while feeding on their pollen and nectar.

Although this damage due to feeding is minor, the main concern arises when they lay eggs in the bark of trees, especially black locust trees.

Their larvae infest and tunnel through tree trunks, compromising the tree structure and health.

In this article, let’s find out whether locust borers can be dangerous to humans.

Are Locust Borers Dangerous to Humans?

Locust borers are insects known for infesting black locust trees, specifically targeting weakened or damaged tree trunks.

Despite causing extensive damage to trees, these insects pose no direct threat to humans as they do not bite or sting people.

To defend themselves, they might nibble the skin without breaking it, which doesn’t cause much pain.

An interesting fact about locust borers is that they mimic the appearance of stinging insects, sporting black and yellow stripes, which helps to deter predators.

Here’s a quick comparison table to illustrate the differences between locust borers and potentially dangerous insects:

Insect Type Bite/Sting Dangerous to Humans Appearance
Locust Borer No No Black and yellow stripes
Some Wasps Yes Can be, depending on allergic reactions Black and yellow stripes

Summarizing the characteristics of locust borers:

  • Long-horned beetle type
  • Larvae tunnel into black locust tree trunks
  • Adults feed on the pollen of goldenrod and other flowers
  • Mimic the appearance of stinging insects (black and yellow stripes)

While locust borers can cause significant damage to black locust trees, they are not harmful to humans as they do not bite or sting.

It is important not to confuse them with other black and yellow-striped insects, like wasps, which can be dangerous depending on the severity of the individual’s allergic reaction to a sting.

Identifying Locust Borers

Appearance

  • Locust borer (Megacyllene robiniae): Long-horned beetle native to North America.
  • Distinctive feature: Yellow markings on black body.

Locust borers are easily recognizable by their black bodies adorned with vivid yellow markings.

These long-horned beetles are native to North America, specifically targeting black locust trees.

Table showing locust borer features

Feature Locust Borer Other Long-Horned Beetles
Markings Yellow on black body Various colors & patterns
Host Tree Primarily black locust Different tree species
Life Cycle One generation per year Varies depending on species

Identifying locust borers is a straightforward process.

Look for their distinctive yellow markings and black bodies, as well as their preference for black locust trees, among other long-horned beetles.

Life Cycle of locust borers

The life cycle of locust borers consists of one generation per year and goes through four stages: egg, larva, pupa, and adult.

  • Duration: One generation per year.
  • Growth stages: Egg, larva, pupa, adult.

This relatively short life span makes it easier for farmers and gardeners to manage infestations.

Life cycle of locust borers

Stage Description Example
Egg Laid in bark crevices End of summer
Larva Feed on tree cambium Autumn months
Pupa Develops in wood Early spring
Adult Active & reproducing Late summer

Damage Caused by Locust Borers

Locust borers are insects that can cause significant damage to certain trees and plants.

They primarily attack black locust trees, but can also infest other host plants such as Osage orange, hickory, and honey locust.

Black Locust Trees

Black locust trees are particularly susceptible to locust borer infestations.

These insects bore into the tree’s bark and tunnel through its branches, causing a weakened structure and potential branch breakage.

Some examples of damages include:

  • Holes in the bark
  • Frass (sawdust-like debris) in bark crevices or around the base of the tree
  • Dead or dying branches

Locust borers are particularly harmful to weakened or stressed black locust trees, which may eventually die from these infestations.

Other Host Plants

Although black locust trees are their primary target, locust borers can also infest other host plants, such as:

  • Osage orange
  • Hickory
  • Honey locust

Damage intensity in different plants

Host Plant Damage Severity Symptoms
Black locust High Holes in bark, frass, branch breakage
Osage orange Moderate Bark damage, tunneling
Hickory Moderate Bark damage, tunneling
Honey locust Moderate Bark damage, tunneling

While the level of damage may vary, these other host plants can still suffer from weakened structures and reduced health.

Therefore, locust borers can cause considerable damage to black locust trees and other host plants.

Managing their infestations is crucial to maintaining the health and stability of these plants.

Feeding and Development of Locust Borers

Locust borers are a type of beetle that is native to eastern North America and primarily feed on the black locust tree.

During their larvae stage, they attack the phloem and xylem layers, creating galleries within the tree.

Adult beetles are not a danger to humans, as they primarily feed on tree sap.

Pupation and Maturation

The larval stage of locust borers lasts for about a year, during which they feed on the tree’s inner structure.

Once they are ready to pupate, the larvae move closer to the bark surface and create pupal chambers.

Features of locust borer pupation and maturation:

  • Pupal stage lasts for a few weeks
  • Adults emerge in late summer or early fall
  • Adults have a wasp-like appearance
  • Adults are black in color with bright yellow bands

Table comparing locust borer with painted hickory borer

Feature Locust Borer Painted Hickory Borer
Host Tree Black locust tree Hickory trees
Season Late summer to early fall Spring
Coloration Black with bright yellow bands Black with cream and yellow markings
Gallery formation In phloem and sapwood In sapwood

Managing and Controlling Locust Borers

Chemical Controls

One method for managing locust borers is by applying chemical controls.

Some common insecticides that may be used for this purpose are:

  • Carbaryl
  • Pyrethroid
  • Carbamate

Applying a carbamate or a pyrethroid insecticide to the bark on the trunk and large scaffold branches in late-July/early-August can help control locust borers. This is done prior to egg laying.

Non-Chemical Strategies

Non-chemical strategies can also be effective in managing locust borers.

Some examples include:

  • Improving tree vigor through proper watering, fertilization, and pruning
  • Pruning infested wood/branches and chipping or burning them to prevent the spread of borers
  • Monitoring for early signs of infestation, such as holes in the bark and reddish frass

Pros and Cons

Chemical Controls Non-Chemical Strategies
Pros:
– Quick and effective for killing the borers
– Can potentially prevent future infestations
Pros:
– Environmentally friendly
– Promotes overall tree health
– Reduces potential for other insect pests
Cons:
– Can be harmful to beneficial insects
– Risk of pesticide resistance
– Chemical contamination concerns
Cons:
– May be slower to show results
– Requires ongoing monitoring and maintenance

Combining both chemical controls and non-chemical strategies can improve the overall effectiveness of your locust borer management efforts.

 

Bug Control Recommendation Tool

What type of pest are you dealing with?

How severe is the infestation?

Do you require child/pet/garden safe treatments (organic)?

Are you willing to monitor and maintain the treatment yourself?


Conclusion

Locust borers are primarily a threat to black locust trees but not to humans.

These insects are longhorned beetles which are known for their distinctive black and yellow stripes that mimic stinging insects, serving as a form of protection from predators.

While their appearance may be intimidating, they pose no direct harm to humans.

It’s essential to understand the nature of these insects and their impact on the environment.

By doing so, we can better manage their population and protect the affected trees, ultimately maintaining a healthy ecosystem.

Footnotes

  1. Locust Borer | Missouri Department of Conservation

  2. Locust Borer – Department of Entomology

Reader Emails

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

Letter 1 – Another Locust Borer

What is this beetle in Montreal, Canada
Hi,
This bug looks beautiful, but is it dangerous?

Had you scrolled down our homepage, you would have found another photo of a Locust Borer, Megacyllene robiniae. The closely related Painted Hickory Borer, Megacyllene caryae, is very similar. It is not dangerous, but it probably does mimic Yellow Jackets for protection from birds.

Letter 2 – Bug of the Month: October 2007 – Locust Borer

Mystery Caterpillar and Bee-Like Insect
Hey Bugman,
I live in Rhode Island, and I’ve run across two odd insects recently. I was wondering if you could help me identify them.
The first was a bright-green and brownish-purple caterpillar with four little spikes on it. It was about an inch long.

The second is a vaguely wasp-like insect (I’m not sure if this is Batesian or Mullerian mimicry, and I didn’t stick around to find out), and it was about an inch long as well. Thanks for your help,
Guillaume Riesen

Hi Guillaume,
Your caterpillar is a Saddleback Caterpillar and we have posted numerous images of this species. Your vaguely beelike insect is a Locust Borer, a Cerambycid Borer Beetle that is very common in the autumn and is often associated with goldenrod. Many beetles in this family are considered wasp mimics.

We believe we are going to make it the Bug of the Month for October and will probably be using your photo on our homepage the entire month.

Letter 3 – Hickory Borer or Locust Borer

Subject: Maybe bee?
Location: Northeastern Ohio
March 20, 2016 1:31 pm
I live in Northeast Ohio and this was in my house this afternoon. Not sure what this is. Looks like a bee but does not look like it has a stinger
Signature: Kim

Hickory or Locust Borer
Hickory or Locust Borer

Dear Kim,
This is one of two species of Longhorned Borer Beetles in the genus
Megacyllene, either a Hickory Borer or a Locust Borer.  Do you have firewood in the house?  If yes, it may be difficult to determine which species you have found.  If you do not have firewood in the house, then this is most likely the Hickory Borer which appears in the spring.  The similar looking Locust Borer is generally present in the autumn.  Both species effectively mimic stinging insects for protection.

Authors

  • 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
Tags: Locust Borer

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