Do Prionus Beetles Bite? Find Out Their Impact on Humans

Prionus beetles are large, destructive insects known for damaging various types of trees due to their feeding habits on tree roots during their larval stage. They mainly cause harm to pecan orchards, which can lead to a tree’s decline over time as their root system becomes weakened. However, the topic of whether Prionus beetles bite is often a question.

Based on the information available, there isn’t any specific indication that Prionus beetles bite humans. While their primary focus is tree roots, it’s important to differentiate them from other beetles, like the Sawyer beetle, that may pose a risk to humans. This distinction can be useful for both amateur and professional entomologists when observing or managing these pests.

Overview of Prionus Beetles

Prionus beetles belong to the Cerambycidae family, commonly known as longhorn beetles, within the order Coleoptera. These beetles are known for their elongated antennae and large size. In this section, we will discuss two primary Prionus species: Prionus Californicus and other Prionus species.

Prionus Californicus

Also known as the California root borer, the Prionus Californicus is a wood-boring beetle native to the western United States. Here are some key characteristics of this species:

  • Dark brown or black in color
  • Length ranges from 1.2 to 2.5 inches
  • Has very long antennae

While they may look menacing, Prionus Californicus beetles generally do not bite humans. However, there are some concerns associated with this species:


  • Larvae feed on decaying wood, helping to recycle nutrients back into the soil


  • Larvae can cause damage to tree roots, affecting plant health

Other Prionus Species

There are several other species of Prionus beetles found around the world, sharing similar longhorn characteristics. Some examples include:

  • Prionus coriarius: a large European beetle also known as the tanner beetle
  • Prionus laticollis: a North American native, commonly referred to as the broad-necked root borer

Here is a comparison table illustrating differences between these two species:

Species Size Range Distribution
Prionus coriarius 0.8-1.6 inches Europe
Prionus laticollis 1.0-1.8 inches North America

Similar to the Prionus Californicus, these other Prionus species generally do not bite humans. However, their presence in an ecosystem can have both positive and negative effects based on their feeding habits and the potential damage they can cause to certain plants or trees.

Lifecycle and Reproduction


Prionus beetles lay their eggs in soil or wood. The female deposits her eggs individually or in small clusters, which ensures the survival of at least some offspring.


Once hatched, the larvae spend years feeding on decaying wood or plant roots. They have a C-shaped body and are creamy-white in color. The larval stage is crucial for the beetle’s development, as it’s the time when they grow and gain energy.


When ready, the larvae undergo pupation, transforming into pupae. During this stage, they develop adult characteristics, such as wings and hardened exoskeletons. Pupation occurs in the soil or the host plant material, providing a safe environment.

Adult Beetles

Now fully developed, the adult beetles emerge from their pupation site. They are active mainly during spring and summer, with a focus on finding a mate. Adult prionus beetles are usually large and have long antennae, making them easy to recognize.


  • Lay eggs in soil or wood
  • Long larval stage
  • Pupation in a safe environment
  • Mating during spring and summer


  • Creamy-white larvae
  • C-shaped larvae body
  • Long antennae in adults
  • Large adult size
Lifecycle Stage Duration Location Main Activity
Eggs Short period Soil or wood Ensure offspring survival
Larvae Few years Decaying material Feeding and growth
Pupation Varies Soil or host Development of adult traits
Adult Beetles Spring/Summer Outdoors Mating and reproduction

Appearance and Identification


Prionus beetles have unique antennae, which are:

  • Long
  • Segmented

For example, the California Prionus has antennae containing 12-20 segments, making it easily identifiable.


These beetles are also equipped with strong mandibles used for:

  • Biting
  • Mating

However, Prionus beetles are not known to bite humans, as their primary focus is mating and laying eggs.

Sexual Dimorphism

Prionus beetles exhibit sexual dimorphism, meaning males and females differ in appearance. Key differences include:

  • Antennae length: Males typically have longer antennae than females.
  • Mandible size: Males often have larger mandibles compared to females.
Trait Male Female
Antennae Longer Shorter
Mandibles Larger Smaller

Keeping these features in mind can help identify and differentiate male and female Prionus beetles in the field.

Do Prionus Beetles Bite?

Potential Harm to Humans

Prionus beetles are not known for biting humans. However, if mishandled or provoked, they may try to defend themselves. While they may possess strong mandibles for chewing wood, their bites rarely cause severe pain for humans.

Predators and Defense Mechanisms

Prionus beetles are equipped with several defense mechanisms against predators. Here are some key characteristics:

  • Thick exoskeleton: Provides protection against smaller predators.
  • Mimicry: Some Prionus beetles resemble more harmful beetles for protection.
  • Strong mandibles: Can be used for self-defense.

Their primary predators include birds, mammals, and other insects. For example, woodpeckers are known to feed on these beetles by flaking the bark off infested trees.

Host Plants and Habitats

North American Distribution

Prionus beetles can be found throughout North America, with their range extending from Alaska to Mexico and from California to Colorado. They inhabit various environments, such as forests, grasslands, and even urban areas.

Deciduous Trees

These beetles are often associated with deciduous trees, like:

  • Oak
  • Pear
  • Other fruit trees

These trees provide both habitat and food for the Prionus beetles, as they feed on their roots and other plant parts.


In addition to deciduous trees, Prionus beetles can also be found on conifers such as fir trees. They feed on roots and cause damage, primarily to younger trees. Some examples of conifers they inhabit include:

  • Fir
  • Pine
  • Spruce
Deciduous Trees Conifers
Oak Fir
Pear Pine
Fruit Trees Spruce

In summary, Prionus beetles are a widely distributed species found across North America. They inhabit various habitats and feed on both deciduous trees and conifers. This makes them a species of concern due to the potential damage they can cause to these host plants.

Damage Caused by Prionus Beetles

Girdling and Root Cambium Feeding

Prionus beetles, also known as longhorned beetles, can cause significant damage to trees through girdling and root cambium feeding. The larvae, known as root borers, tunnel into the root cambium of a tree, cutting off nutrient and water uptake.

  • Girdling: Prionus beetles cause girdling by removing the cambium layer of roots, creating a barrier in the flow of nutrients.
  • Root Cambium Feeding: Larvae feed on root tissue, impacting the tree’s ability to absorb water and nutrients.

Water Stress, Wilting, and Yellowing

Trees infested by root borers like California root borers may exhibit symptoms such as:

  • Water Stress: Trees struggle to take up water due to damage to their roots.
  • Wilting: As water uptake reduces, leaves become limp and droopy.
  • Yellowing: Insufficient nutrient absorption leads to chlorosis, making the leaves yellow.

Tree Death and Disease

An infestation of Prionus beetles and the damage they cause can eventually lead to tree death. Additionally, the weakened state of an infested tree makes it more susceptible to diseases and other pests.

Examples of damage caused by Prionus beetles:

  • Pine trees infested by pine sawyers, a type of long-horned beetle, may exhibit a decline in health and eventually die.
  • Fruit and nut trees attacked by Prionus beetles may experience reduced yields.

Pros of Prionus beetle control methods:

  • Using pheromone traps can help monitor and manage adult beetle populations.
  • Mechanical removal of infested trees can help prevent the spread of tree diseases.

Cons of Prionus beetle control methods:

  • Insecticide applications often have limited effectiveness and may harm beneficial insects.
  • Preventative measures can be costly, requiring long-term monitoring and maintenance.

Comparison Table: Prionus Beetle Control Methods

Method Pros Cons
Pheromone Traps Effective in monitoring populations Limited in reducing larvae infestations
Tree Removal Helps prevent disease spread May not fully eliminate beetle populations
Insecticides Can reduce beetle populations May be harmful to beneficial insects and bees

Attractants and Detractors

Pheromone Traps

Prionus beetles are known to be attracted to certain pheromones. This characteristic has allowed researchers and pest management professionals to develop pheromone traps as an effective tool for beetle detection and control.


  • Target specific species
  • Environmentally friendly
  • Easy to use


  • Not a complete solution
  • Must replace lures regularly
  • May attract non-target species

Here’s an example: An entomologist might place a trap containing synthetic pheromones in a location with a high density of tree bark, providing better odds of attracting and capturing prionus beetles.

Light Attraction

Prionus beetles are also known to be attracted to lights. This feature makes light traps another potential option for managing beetle populations.


  • Simple to set up
  • Can be cost-effective


  • Attracts a variety of insects (may be less selective)
  • Can be disruptive if improperly placed

An example of light attraction in action might be placing a blacklight or mercury vapor bulb near an area of concern, and observing the increase in activity of prionus beetles during the night.

Attraction Method Specificity Environmental Impact Ease of Use
Pheromone Traps High Low High
Light Attraction Moderate Variable Moderate

To summarize, both pheromone traps and light attraction can be used to effectively monitor and manage prionus beetle populations. While pheromone traps may provide more specificity, light attraction can also be a useful management tool in certain settings.

Control and Management Strategies

Pesticides and Chemical Control

Pesticides can be an effective means of controlling Prionus beetles. For instance, systemic and bark-penetrating pesticides are utilized on unbaited or pheromone-baited trees to kill beetles under the bark. Yet, always use caution when applying chemicals, especially near homes and gardens.


  • Quick and efficient control of beetles
  • Wide range of products available


  • Potential harm to the environment and non-target organisms
  • Possible pesticide resistance in beetles

Physical Barriers

Physical barriers can help prevent infestations by blocking access to beetle’s preferred breeding and feeding sites. For example, placing a screen or mesh around firewood stacks can protect them from incoming beetles.


  • Non-toxic and environmentally friendly
  • Reusable and cost-effective


  • May require regular maintenance and adjustments
  • Not 100% effective in blocking all beetles

Cultural and Biological Control

Cultural control practices aim to disrupt the beetle’s life cycle and habitat. This might include:

  • Removing infested wood and debris
  • Sanitizing pruning tools to minimize spread

In terms of biological control, natural predators like birds and predatory insects can assist in managing prionus beetle populations. Encouraging these beneficial species in your garden or yard can help keep the beetles at bay.


  • Environmentally friendly
  • Promotes biodiversity


  • Might not provide immediate results
  • Biological control agents can also have non-target effects

Comparison Table:

Control Method Pros Cons
Pesticides and Chemical Control Quick and efficient control; Wide range of products Harm to the environment and non-target organisms; Possible pesticide resistance
Physical Barriers Non-toxic and environmentally friendly; Reusable and cost-effective Requires maintenance; Not 100% effective
Cultural and Biological Control Environmentally friendly; Promotes biodiversity Might not provide immediate results; Possible non-target effects on beneficial species

Resources and Further Information


  • One great resource for information on beetles is the BugGuide website.
  • It offers details on various species, including the Tile Horned Prionus.

Tile Horned Prionus

  • The Tile Horned Prionus (Prionus imbricornis) is a type of longhorn beetle.
  • Adults of this species are known to feed on dead wood, but the larvae feed on the roots of trees, making them a potential threat to gardens and orchards1.

Blister Beetles and Related Species

  • Blister beetles are different from prionus beetles because they belong to the family Meloidae.
  • These insects produce a defensive chemical called cantharidin2.

Comparison of Prionus and Blister Beetles

Feature Prionus Beetles Blister Beetles
Family Cerambycidae Meloidae
Notable Features Long antennae Cantharidin secretions
Behavior Larvae feed on tree roots Adults feed on plants, can be harmful to people and animals when ingested

Giant Root Borer

  • The Giant Root Borer (Prionus californicus) is another large beetle species found in North America3.
  • Its larvae feed on the roots of trees, including fruit and nut trees.

Characteristics of the Giant Root Borer

  • Appearance: Dark brown to black, around 2 to 3 inches in length
  • Habitat: Forests, orchards, and woodlands
  • Lifespan: Larval stage can last up to 3 years, while adult beetles live only a few weeks





Reader Emails

Over the years, our website, 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 – A new species for What’s That Bug? Prionus fissicornis


Subject: Large brown beetle
Location: Linton, North Dakota
June 18, 2016 9:45 pm
Linton ND June 18, 2016 10pm. Large brown beetle close to a shop light laying on the ground.
I’ve never seen a beetle this large in ND before. I’m just wondering what it was. It was about 1.5″ long with fuzzy “feelers” that were about an inch long each.
Signature: Eric Jensen

Prionus fissicornis
Prionus fissicornis

Dear Eric,
This is one of the Root Borers in the genus Prionus, and though we have countless examples on our site, we are thrilled that we have identified your individual on BugGuide as Prionus fissicornis because it has so many segments on its antennae.  According to BugGuide:  “ant[ennae] w/ at least 25 antennomeres (‘antennal segments’), often over 30.”  Your individual is a male.  BugGuide also notes:  “Larvae are root feeders on grasses” and “Adults active May-July.”  Beetles in the Bush has an entertaining account on this species.  Your submission represents a new species for our site.

I’ll try to get a better picture of one for you with our 35mm camera. It should be way clearer than the first picture I sent.
Thank you very much for replying. I appreciate it!

Letter 2 – Possibly Prionus heroicus from Utah


Subject:  Beetle ID
Geographic location of the bug:  Lindon, UT near Wasatch Mountains
Date: 07/27/2018
Time: 06:02 PM EDT
Your letter to the bugman:  After watching fireworks (July) we came back to our garage to find this beetle inside. We’ve never seen this large of a beetle around here. It was about 1.5 inches long, could fly, didn’t walk too fast. I can’t remember what the underside looked like.
How you want your letter signed:  CuriousPence

Prionus heroicus, possibly

Dear CuriousPence,
This is one of the Longicorns in the genus
Prionus, and the dark color and Utah sighting has us speculating it might be Prionus heroicus which is pictured on BugGuide.

Letter 3 – Prionus Beetle


This is an email forwarded to me by my aunt who found this interesting species of wasp in her backyard…Any ideas???
I know you will think I’m being weirder than usual, but I happen to find all animals (even insects) very fascinating even the freaky ones!!
I was outside this am playing and cleaning up my Danes, then started cleaning the pool. I found this bug dead in one of the baskets. Talk about freaky!!!!!!!!!! Has anyone ever seen this or know what family of insects it is from? Its back-end is striped like a yellow jacket, but its huge!! It measures 3.5 cm from the tip of its tail to its mouth, and it has 2 different sets of wings, the back wings are clear with dark brown veins and are 2.5 cm long, and its front wings are dark brown/red and are 2 cm long but are shaped differently than its back. its long feelers/antennas are almost 3 cm long. and it has HUGE jaws (I think they are called mandibles) but science was a LONG time ago for me. It also appears to have a stinger out its back-end! WOE
~~~~ Debbie”

Hi Rachel and Debbie,
You found a Prionus which is a member of the Long Horned Borer Beetle family. These are among the largest beetles in California as well as other parts of the U.S. The grubs bore into the roots of Oaks, Madrone, Cottonwoods and some Fruit Trees. They will also feed on Eucalyptus. Adults emerge in summer and are often attracted to lights, which might explain its drowned presence in the pool.

Ed. Note: We just recieved this information.
(08/09/2005) identificationsHello – I was recently shown your site, and it is excellent. My specialization is longhorned beetles, and in cruising around I notice a number of incomplete or uncertain IDs for this family. I don’t know if you are interested in receiving this sort of input, but if you are, I offer the following additions to your identifications.
The beetle pictured is Prionus (Neopolyarthron) imbricornis (or much less likely, P. (N.) debilis; that level of detail is lacking in the photo), but with that many antennal segments, cannot be either of the two Californian Prionus (Prionus) species. Cheers.
Frank Hovore


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. 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

Leave a Comment