Prionus Beetle: All You Need to Know – Quick Guide on Biology and Control

The Prionus Beetle, a large, robust reddish-brown insect, belongs to the family Cerambycidae and is known for its long, tiled antennae. Females are typically larger than males, while males possess larger antennal segments in comparison to their female counterparts. With several similar species found in New Mexico, this beetle is an interesting subject for entomology enthusiasts and researchers alike .

Adult Prionus Beetles are typically monitored with light traps, including UV and incandescent traps, as they usually take flight soon after sunset. Their activity tends to decline after midnight, likely due to dropping temperatures, and can be observed from late June to early August .

Prionus Beetle Biology

Life Cycle

The Prionus Beetle goes through four stages in its life cycle: egg, larva, pupa, and adult.

  • Eggs: Laid by females, typically in wood
  • Larvae: Present in wood year-round, varying in size and appearance
  • Pupae: Develop from larvae, forming a protective casing
  • Adults: Occur in mid-summer, with males and females having different features


Sexual Dimorphism

Prionus Beetles exhibit sexual dimorphism, meaning that males and females have distinct physical traits.

  • Females: Larger than males; may have slightly shorter antennae
  • Males: Smaller than females; possess larger antennal segments



The Prionus heroicus is a very large, robust reddish-brown beetle. Males of this species have substantial antennal segments.


Adult Activity

Adult Prionus Beetles are typically active from late June to early August.

  • They can be monitored using light traps (UV and incandescent)
  • They usually fly soon after sunset
  • Trap-catch declines after midnight, likely due to colder temperatures


Description and Appearance

Cylindrical Body

Prionus beetles are known for their large, robust, and cylindrical body. They vary in size depending on the species, with some being quite large like the Prionus heroicus.

Serrated Antennae

These beetles have long, tiled antennae that are serrated. The male Prionus beetles typically have larger antennal segments compared to the females.


Prionus beetles have six legs, like other insects in the Hexapoda class. Their legs are sturdy and strong, allowing them to navigate various terrains and search for food.


Although there are variations among species, the California Prionus, for example, exhibits a reddish-brown coloration. This can help them blend in with their surroundings, such as tree bark and soil.

In summary, Prionus beetles exhibit key features such as:

  • Cylindrical body
  • Serrated and long antennae
  • Sturdy six legs
  • Reddish-brown coloration

Species like the California Prionus display these characteristics, making them a fascinating subject for entomologists and nature enthusiasts alike.

Diet and Feeding Habits

Feeding on Roots

Prionus beetles primarily feed on the roots of various plants, including trees, shrubs, fruit trees, and conifers. Their larvae are known to be particularly voracious, causing damage to the root systems of their host plants. Some examples of plants they feed on include:

  • Apple trees
  • Cherry trees
  • Pine trees
  • Oak trees

Host Plants and Preference

Prionus beetles show preference for certain host plants. For instance, the larvae are more likely to feed on the roots of fruit trees than conifers. Here’s a comparison table of host plants:

Host Plant Type Prionus Beetle Preference
Fruit Trees High
Conifers Low
Deciduous Trees Medium
Shrubs Medium

Pros of Prionus Beetle Feeding Behavior:

  • Help decompose dead or weakened plants, providing nutrients for other organisms.

Cons of Prionus Beetle Feeding Behavior:

  • Damage and weaken healthy plants.
  • Cause economic losses for farmers and gardeners.
  • Infestations difficult to control.

Distribution and Range

Geographical Distribution

Prionus beetles are found throughout North America, with various species having their own unique geographic ranges. Populations can be found from coast to coast, including regions such as Alaska1. The distribution of Prionus beetles is influenced by the availability of their preferred host plants.

Host Plant Associations

These beetles are known for having a broad host range. They infest various deciduous trees, shrubs, and some conifers and brambles2. Some common host plants include:

  • Oak trees
  • Cherry trees
  • Apple trees
  • Peach trees
  • Maple trees

Pros of diverse host range:

  • Adaptability in various ecosystems
  • Availability of food sources for the beetle

Cons of diverse host range:

  • Potential damage to a wide variety of tree species
  • Difficulty in controlling infestations due to numerous host plants

Below is a comparison table of two common Prionus species and their preferred host plants.

Species Preferred Host Plants
Prionus californicus Oak, Cherry, Apple, Peach, Maple
Prionus laticollis Oak, Hickory, Maple, Ash, Elm

Impact on Agriculture and Forestry

Damage to Crops and Livestock

The Prionus beetle can cause significant damage to agricultural crops, such as fruit trees and conifers. They can harm tree roots and weaken plants, leading to reduced yields.

For example, damage to fruit trees includes:

  • Stunted growth
  • Reduced fruit production
  • Weakened root systems

Livestock can also be affected when they consume forage and hay that’s contaminated with Prionus beetles. Ingesting these beetles can lead to toxic effects, such as:

  • Blisters
  • Inflammations
  • Life-threatening conditions1

Infestation in Commercial Forests

Prionus beetles also infest commercial forests, targeting pine and spruce trees2. This can lead to severe losses and long-term impacts on the forest ecosystem.

The infestation in commercial forests causes:

  • Destruction of tree bark
  • Weakened trees that become susceptible to other pests and diseases
  • Detrimental effects on timber production

Comparison of Impact on Agriculture and Forestry

Impact Agriculture Forestry
Damage to crops Fruit trees, conifers Pine, spruce trees
Effect on livestock Toxic effects when consumed Not directly affected
Economic consequences Reduced yields, crop losses Decreased timber production

Detection and Monitoring

Documentation and Reporting

  • To detect Prionus beetles, monitoring is crucial.
  • When beetles are found, timely documentation and reporting are necessary.

Examples include:

  • Taking clear photographs of suspected beetles
  • Recording the date and location of the sighting

A comparison table of different documentation methods:

Method Pros Cons
Photographs Visual evidence May require expert ID
Written records Detailed information Can be time-consuming
GPS coordinates Accurate location data Accessibility to GPS

Use of Pheromone Traps

  • Pheromone traps help capture and monitor Prionus beetles.
  • They contain chemical signals that mimic beetle pheromones.

Pros and cons:

  • Pros: Effective, species-specific, user-friendly
  • Cons: Require regular maintenance, potential for disruption


  • Placing traps around the perimeter of the infested area
  • Strategically positioning traps near host plants

Characteristics of pheromone traps:

  • Lure beetles using species-specific chemical signals
  • Typically designed to trap target species only
  • Can be used for ongoing monitoring and population control

Prionus Beetle Management

Cultural and Mechanical Practices

  • Regularly inspect trees and shrubs for signs of infestation.
  • Maintain healthy plants to reduce their vulnerability.
  • Prune and remove dead or infested branches to decrease beetle populations.
  • Properly dispose of infested wood, as the beetles can overwinter in this undergrowth.

Chemical and Biological Controls

Chemical Controls

  • Apply registered insecticides to susceptible trees during adult emergence.
  • Exercise caution when using chemicals to protect non-target organisms.

Biological Controls

  • Introduce predators like lady beetles and lacewings which feed on Prionus beetle larvae.
  • Foster a diverse landscape to support these predator populations, improving the overall quality of your beetle management strategy.
Method Pros Cons
Cultural & Mechanical Environmentally friendly May not eliminate large infestations
Chemical Controls Can target specific pests May harm non-target organisms
Biological Controls Sustainable, long-term solution Requires diverse landscapes

Taxonomy and Related Species

Subfamily Prioninae

The Prionus Beetle belongs to the subfamily Prioninae, which is a part of the long-horned beetles family, Cerambycidae. This subfamily includes:

  • Prionus root borer
  • Round-headed borers

Tribe Prionini

Within the Prioninae subfamily, the Prionus beetle is a member of the tribe Prionini.

Genus Prionus

The beetle’s genus is Prionus, which contains various species with similar features and characteristics.

Key Species

One key species within the Prionus genus is the Prionus californicus, also known as the California Prionus.

Features of Prionus californicus:

  • Large size
  • Long antennae
  • Active from late June to early August
Features Prionus californicus Other Prionus species
Size Large Varies
Antennae Long Long
Active season Late June – August Varies

Prionus californicus primarily attacks tree roots, causing damage to various agricultural crops and trees. The pros and cons of its presence are:


  • Part of the natural ecosystem
  • Can help with breaking down dead plants


  • Can cause damage to crops and trees
  • Can be an agricultural pest


  1. 2

  2. 2

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 – Prionus, but what species???


Subject:  Prionus?
Geographic location of the bug:  Carbondale, Colorado
Date: 07/26/2018
Time: 01:18 AM EDT
Your letter to the bugman:  Hi, is this a prionus beetle? Is it possible to tell what kind? It was very large and hissed when I tried to hurry it along from our front door. Thank you!
How you want your letter signed:  Megan

Prionus species

Dear Megan,
We agree that your beetle is in the genus
Prionus, but we are not certain of the species.  BugGuide lists 16 species in North America.  Perhaps one of our readers will be able to provide a species identification.

Prionus species

Letter 2 – Prionus emarginatus: The Saga Continues!!!


Prionus emarginatus
Hi Guys,
Well not as many as last night but close! I have collected I think 10-12 but they are hard to count :0) Vicki took a few more pictures (actually over 100) but I thought I would send along her best. They are taken in a white container again but not a white box so it shows a reflection against the container. The grass in it is Timothy hay. I will try to keep them alive until you tell us what to do with them. I am flattered that you thought I could actually photoshop in the hairs but one of these shows the bottom of the bug too and it is also hairy. No Photoshopping was done, it is simply cropped down from an 8MP digital camera on macro lens in iPhoto on a Mac computer. Also these are a little smaller than the one we caught last night, but we let him go after taking the pictures of him.

This is the info that can be posted with the photos (as Eric wants to make a page of this particular beetle) Photographer: Victoria Lawson-Petit Date: July 2-3, 2008 Weather: Afternoon and early evening heavy summer rains Time: 9-9:30 pm Attraction: Porch light (they just come in my house under screen door) Where: Elbert, Colorado 80106 Elevation: 6750 ft. We are on the Arkansas Divide (a small mountain range that juts out into the Eastern Plains of Colorado) (Arkansas River goes south / Platte river goes north of this divide) Terrain: foothills, ponderosa pine and a few other varieties of pine, Oak along the creek, the area is also known for its Chokecherry bushes, Farm and Ranch land is 90% of Elbert, County. Camera: Polaroid 8MP digital camera with macro lens.

Wow Jo,
Vicki did a wonderful job on the new photos. If she decides to study photography in the future, I am chair of Media Arts at LACC and I teach photography.

Update: (07/06/2008)
In looking up the potential candidates for the lepturine longhorned beetle, I used “A Survey of the Cerambycidae (Coleoptera), or Longhorned Beetles, of Colorado,” (the first installment of a series entitled Insects of Western North America), by Daniel J. Heffern, 1998, published by the Gillette Museum of Arthropod Diversity, Department of Bioagricultural Sciences and Pest Management Publications (geez, what a mouthful!). Anyway, I decided to see what it had to say about Prionus emarginatus: “Type Locality [where the specimen first described to science was collected]: ‘Arkansas River near the Mountains.’ Hosts: Oryzopsis. Craighead (1923) reports larvae being associated with grasses. Discussion: Gwynne and Hostetler (1978) describe a mass emergence of this species in the Great Sand Dunes National Monument. Its life cycle apparently requires three years. Distribution: AZ, CO, ID, NE, NM, WY….” Feel free to add whatever is appropriate to the “ongoing saga,” or don’t….

Letter 3 – Prionus emarginatus trio


Prionus emarginatus – A Female!
Hi Daniel, Bob and Eric,
I am writing to share one more round of photos. These are Vicki’s best shots out of at least 50! Vicki found this at her boyfriends house, which is 2 miles west of our house, more in the farm lands as we live in the little town. Their house is surrounded by Timothy Hay fields. She is not as fuzzy underneath but there is hair there.
Elbert, Colorado

Hi Jo,
That female is sure a behemoth. We have been very busy preparing for our Getty lecture and have not had time to check emails. We are curious about the size difference between the males and the female. Did Bob or Eric write back with any comments?

We would love to hear from an expert on this. Since we were totally unaware of this unusual Prionid before your original letter, we wonder if this degree of sexual dimorphism is typical, or if this is a female of anther species in the genus.

Hi Daniel,
Actually they both answered back. I have also sent this beetle and a few males to Bob as requested so he will be able to confirm as far as a novice could tell she were mating with the two males for about an hour. Eric Said: “Holy cow! That is the most incredible sexual dimorphism I have ever seen in that genus! I had no idea….” Bob Said: “COOL!!!! I’ve never seen a female of that species

Letter 4 – Prionus imbricornus


I found this beetle(?) on my back patio by my sliding glass door. I am extremely scared of bugs, any type, but I have never seen anything like this before. I live in South Florida (Port Saint Lucie) my backyard has a canal with a lot of trees and bushes. It looks to be around 25 mm in length, it is redish brown with long antennae that curl around and touch the ground. Sorry about my description, I try to stay away and know as little about bugs as possible. The picture may not be great but I was scared to get too close. I have attached it. Let me know if you need a better one and I will try my best.
Thank you, Kim

Hi Kim,
What a beautiful Long Horned Borer you have. The species is Prionus imbricornis. These are large reddish beetles. Your species is a male, identified by his longer, thicker antennae. Larger specimens can reach nearly two inches in body length. The larvae bore in oak, chestnut and other hardwood trees. They also live in roots of herbaceous plants.


  • 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.

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    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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