The brown prionid, also known as Orthosoma brunneum, is a fascinating insect belonging to the longhorn beetle family.

Not only are they an exciting discovery for bug enthusiasts, but they also play a vital role in the ecosystem.

Brown prionids are known for their distinct elongated antennae, which make them easily identifiable.

These beetles are primarily found in the wooded areas of North America, where they contribute to the natural process of breaking down and recycling dead wood material.

In their natural habitat, brown prionids have certain advantages and disadvantages.

These beetles assist in decomposing wood, providing essential nutrients to the soil. However, on the downside, they can sometimes damage healthy trees if their population increases uncontrollably.

Brown Prionid: Basic Information

Classification and Scientific Name

The Brown Prionid (Orthosoma brunneum) belongs to the order Coleoptera and the family Cerambycidae. Specifically, it falls under:

• Kingdom: Animalia
• Phylum: Arthropoda
• Class: Insecta
• Order: Coleoptera
• Family: Cerambycidae
• Subfamily: Prioninae
• Tribe: Prionini

Physical Description

The Brown Prionid is known for its distinct antennae. These beetles have:

• Brown coloration
• Elongated body shape
• Body length: 20-50mm
• Wing patterns: Brown with variable markings

Physical features of the Brown Prionid include:

• Long and straight antennae
• Robust body structure
• Its mandibles are Large and curved

The bug uses its large mandibles for fighting and mating. Their antennae are especially noticeable due to their length and segmentation.

Compared to other beetles in the Cerambycidae family, the Brown Prionid’s antennae are relatively shorter.

Distinctive Sound

The Brown Prionid is known for its squeaking sound. This sound is produced using a method called stridulation:

• Rubbing its wings against its abdomen
• Utilized for communication and attracting mates

Life Cycle and Behavior

Eggs and Larvae

The life cycle of the brown prionid begins with the female laying eggs. These eggs are typically laid near decaying wood or roots of trees, like oaks.

Upon hatching, the larvae emerge and start feeding on roots and decaying wood. Some key characteristics of the larvae are:

• Creamy white color
• C-shaped body
• Well-developed mandibles

Larvae prefer feeding on the roots of various trees and shrubs, providing them with essential nutrients.

Pupa and Adult

After reaching a certain size, the larvae undergo pupation and transform into pupae.

Pupation occurs mainly in the soil, near the food source. Key features of the brown prionid pupa include:

• Exarate (free) appendages
• Inactive and immobile stage

The pupal stage is followed by the emergence of adults. Adult brown prionid beetles are nocturnal, meaning they are active during the night.

Some features of the adult brown prionid include:

• Brownish-black color
• Robust body, measuring up to 2 inches in length
• Attracted to light sources

Life Stage	Characteristics
Egg	Laid near decaying wood or roots of trees, like oaks
Larva	Creamy white, C-shaped, feed on roots and decaying wood
Pupa	Exarate appendages, inactive, mainly in the soil near a food source
Adult	Brownish-black, robust body, nocturnal, attracted to light sources

The typical lifespan of a brown prionid beetle ranges from one to two years, depending on the availability of food and environmental conditions.

Habitat and Distribution

Native Range

The brown prionid (Orthosoma brunneum) is a native species primarily found in North America. Its range extends from Maryland in the north to Howard County in the south

This beetle thrives in areas with decaying wood, especially moist and rotting wood, which is essential for its growth and development.

Habitats

Brown prionids prefer habitats with abundant decaying wood, which they use for shelter, reproduction, and as a source of food. Some key habitat features include:

• Moist: Brown prionids require moisture to survive, and they can be found residing in damp and decaying wood.
• Decaying Wood: They are commonly found in environments with ample decaying wood, such as forests and woodlands.

Some examples of their preferred habitats include:

1. Forests with rotting logs
2. Old lumber piles
3. Tree stumps in various stages of decay

Brown prionids can sometimes be found in residential areas if there is a sufficient abundance of decaying wood.

The brown prionid’s native habitat is essential for its survival, and maintaining a healthy ecosystem with decaying wood ensures their continued existence.

Diet, Damage, and Predators

Feeding Habits

The brown prionid beetle feeds primarily on decaying wood, plant roots, and sometimes bark. It is commonly found in forests and wooded areas.

• Diet includes:
  • Decaying wood
  • Plant roots
  • Bark

Potential Harm

Brown prionid beetles can cause minor damage to trees and plants due to their feeding habits. However, they are not considered a significant threat to forests or agriculture.

• Minor damage to:
  • Trees
  • Plants

Natural Predators

Brown prionid beetles have several natural predators, which help control their population in the ecosystem.

• Predators include:
  • Birds
  • Small mammals
  • Flies

For instance, certain fly species lay eggs in the larval stage of the brown prionid beetles, consuming and limiting their population growth.

Human Interaction

The Brown Prionid beetle, while primarily a dweller of forests and wooded areas, occasionally comes into contact with humans, especially in regions where their habitats overlap with populated areas. Here’s a closer look at these interactions:

Pest or Friend?

Generally, Brown Prionids are not considered harmful pests to humans. They don’t bite or sting, and their primary diet consists of decaying wood and plant roots.

However, in areas where they are abundant, their larvae might cause minor damage to tree roots or garden plants.

On the positive side, by feeding on decaying wood, they play a role in the natural decomposition process, recycling nutrients back into the soil.

Attraction to Lights

Like many beetle species, Brown Prionids are attracted to artificial lights. It’s not uncommon for residents in areas with a significant Brown Prionid population to find these beetles buzzing around porch lights or street lamps during the night.

This can sometimes lead to accidental home invasions, especially during warmer months when windows and doors are frequently left open.

Conclusion

The brown prionid, scientifically termed as Orthosoma brunneum, is a captivating member of the longhorn beetle family, predominantly found in North America’s wooded regions.

Recognizable by its elongated antennae and brown hue, this beetle plays a pivotal role in the ecosystem by aiding in the decomposition of dead wood.

While they do have a penchant for decaying wood, plant roots, and bark, their impact on trees and plants is relatively minor. However, their presence can sometimes be a concern if their population surges uncontrollably.

By understanding their life cycle, habitat preferences, and behavior, we can appreciate their role in nature and manage their presence effectively.

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 – Tile Horned Prionid

palmetto-like bug with fuzzy antennae
Jul 10, 2009
palmetto-like bug with fuzzy antennae
These interesting critters parked themselves on our door after a rainy day. They were bigger than the roaches we have here in the south. We haven’t seen them since that night. We were wondering what these rare insects are called.
Thanks from Clemson
South Carolina

Hi Clemson
This is one of the Root Borers in the genus Prionus, the Tile Horned Prionus, Prionus imbricornis.  You may read more about this species and its relatives on BugGuide.

Letter 2 – Brown Prionid

Subject: American Cockroach Poser
Location: Dobbs Ferry, New York
July 15, 2014 6:56 pm
Hi!
So the other night (low 80 degree night, pretty humid, on July 14th) I was sleeping in my basement when I woke up to an insect crawling over my face and on my body. I proceeded to jump out of bed, scream and run to my couch (I’m not a huge bug fan) about 30 seconds later the bug crawled across the bed and took flight (clumsy flight) towards a different part of the room.

We’ve been living in Westchester, NY (about 17 miles north of new york city) for over 17 years and have never seen a cockroach, our basement is pretty dry as far as basements go and we keep it pretty clean, however, there are a number of american cockroaches in my local middle and high school.

When inspecting the bug after we had caught it a day later I noticed its antennae did not match the american cockroach. Is this a beetle? Or possibly another species of bug? I’m extremely curious and confused, any information would be greatly appreciated.
Signature: Clara Winder

Dear Clara,
This impressive beetle is a Brown Prionid.  Though they are not considered dangerous, they have strong mandibles that may give a painful bite, possibly even drawing blood, if they are carelessly handled.

Letter 3 – Brown Prionid

Long, sedentary beetle in NJ
July 4, 2010
Hi,
I trolled BugGuide with no success. This critter, with a length of about 3 or 4cm, stayed stationary all evening. It was about 70F with moderate humidity on a clear night.
Thanks, and happy 4th!
Greg in NJ
Central NJ

Good Morning Greg,
Your beetle is the Brown Prionid, Orthosoma brunneum, and it can be recognized, according to BugGuide, by “Light brown, sides of elytra parallel. 11-segmented antennae, rounded, never flattened.“

Letter 4 – Brown Prionid

Subject: Huge Beetle Found! Invasive or Not?
Location: Eastern United States, DE
July 22, 2014 11:06 pm
Hello! I’ve got a bug on my hands – well, in a jar – and I don’t know what to do with it.
I have lived in this area for 20+ years and am an avid outdoorswoman. This critter was trying to get into my house through the window screen, and I’d like some expert help figuring out just what it is.

Because I’ve never, ever seen it before.
This beetle is large, nearly two inches long, with a slender body about half an inch wide. It’s a rusty reddish brown color, with black mandibles and antennae about an inch long. There are no discernible markings.

I’ve confirmed that it is not a cockroach of any variety, and if it didn’t have terrifying looking mandibles I’d be picking it up to take better photos.
I’d like to know if it’s a type of boring beetle or not, so I can know if it’s invasive or not. I’ve never seen it before and it’s rather concerning to see something this…enormous on my window trying to nibble the screen.

Any info pointing me in the right direction would be awesome. 🙂
Signature: ~ Kat of the Coast

Dear Kat of the Coast,
Root Borers in the family Prioninae are quite impressive beetles and there are several native species found in Delaware, even if they have managed to avoid detection by you in the past. 

This is a Brown Prionid, Orthosoma brunneum, and you are wise to avoid its mandibles.  The grubs of Root Borers live feeding on wood for several years and the mandibles of the adults need to be strong enough to chew their way to the surface once metamorphosis is complete. 

We suspect this individual was attracted to light, and that is why you discovered it on your screen.  See BugGuide for additional information on the Brown Prionid.  We would urge you to release your captive Brown Prionid.

Letter 5 – Brown Prionid

Subject:  What is this?
Geographic location of the bug:  North Carolina
Date: 06/27/2019
Time: 01:33 PM EDT
Your letter to the bugman:  What is this???
How you want your letter signed:  Signed,

This is one of the large Prionid Beetles that appear each summer in many parts of North America.  Your individual is a Brown Prionid, Orthosoma brunneum. 

Letter 6 – Brown Prionid

Subject:  Large Long Brown Beetle
Geographic location of the bug:  Georgia
Date: 07/03/2019
Time: 11:19 PM EDT
Your letter to the bugman:  Saw this large guy (over 2 inches long!) chilling on our house. I tried googling him but there are so many generic brown beetles it’s hard to narrow him down. Any thoughts?
Thanks!!
How you want your letter signed:  Vika

Dear Vika,
The Brown Prionid is a relatively common summer identification request from the eastern parts of North America.

Letter 7 – Prionid from Puerto Rico

Subject: Type of beetle?
Location: Dorado, Puerto Rico
May 18, 2014 3:37 pm
We found this beetle on the wall od our terrace, what kind is it?
Signature: Pili

Dear Pili,
Your beetle reminds us of a North American Prionid known as the Hardwood Stump Borer, Mallodon dasystomus, so we tried to search for Puerto Rican species, and we found a reference on Prioninae of the World to a Puerto Rican species, Nothopleurus maxillosus, formerly known as Mallodon maxillosum.

An image of a Brazilian relative, Nothopleurus lobigenis, that we found on Cerambycidae Species looks very similar to your individual.  Continued searching brought us to an image on the Worldwide Cerambycidae Photo Gallery that looks very close to your image and it is identified as Hovorodon bituberculatum.  We would not rule out Stenodontes exsertus also found on the Worldwide Cerabmycidae Photo Gallery.

Letter 8 – Brown Prionid

Subject: Unknown Beetle?
Location: Lebanon, Maine
August 4, 2014 5:43 pm
Hello, I was searching in my basement for old things and I came across this big guy. My basement is rather moist from the humidity and has a lot of old cardboard boxes around.

This creature is about one inch in length excluding the antennas and looks around 2 millimeters in width. It has six legs and a nice little jaw bone look that normal beetles have. Looks along the lines of a soldier beetle but different colors. I’d appreciate it if you could help me out here. I’d be pretty freaked if it were a cockroach.
Signature: Yours truly.

Dear Yours truly,
Images of Brown Prionids, Orthosoma brunneum, like the one you submitted, continue to pour into our site for identification.  Though they are not considered dangerous, Brown Prionids, like many other members of the Longhorned Borer family Cerambycidae, have very powerful mandibles and they might draw blood from a bite if carelessly handled.

Letter 9 – Prionid from Zimbabwe

Subject: Longhorn beetle
Location: Philadelphia, Harare, Zimbabwe
January 31, 2017 6:14 am
I have narrowed down the identity of this beetle to Tithoes Confinus or Tithoes Maculatus. What do you think?
Signature: Majotso

Dear Majotso,
We have several Prionids from Africa in our archives that we have identified as Tithoes confinus, but we would always defer to true experts when it comes to determining the exact species. 

Many times members of the same genus require close examination to determine an exact identity and we just do not possess the necessary qualifications to make that determination.  Perhaps one of our readers will be able to provide more specifics.  This posting from our archives has some information on distinguishing T. confinus from T. maculatus. 

ISpot has many postings from the genus, and not a single one is identified as T. maculatus, and several are identified as T. confinus.  Prioninae.org does have an image of a pair of T. maculatus, and the range is listed as “Angola Bénin Burkina Faso Cameroun Centrafrique Côte d’Ivoire Gabon Gambie Guinée BIssau Mali Niger Nigeria Rwanda Sénégal Soudan Tchad Togo” and not Zimbabwe.

Thank you Daniel,
I posted this pic on NatureWatch NZ and got feedback from Jacob and fubr as being T. maculatus frontalis which I now agree with.
Regards,
Majotso

 

Letter 10 – Prionid from South Africa may be Anthracocentrus capensis

Subject: BIG bug!
Location: Gamkaskloof (Swartberg), Western Cape
February 26, 2017 9:18 am
Hi,
What exactly is this large beetle with big pincers please?
George
Signature: No preference

Dear George,
This is a Root Borer in the subfamily Prioninae, and we believe that based on images posted to iSpot, Anthracocentrus capensis is a likely species identification.  A note on iSpot states: 

“In case you may miss some scale in this picture, this is an enormous beetle in excess of 80mm long, and one of the very largest beetles in southern Africa. The individual here is a female; the male bears even considerably longer mandibles (“jaws”).”  There is a nice comparison image showing the male and female on Prioninae.org.

Letter 11 – Brown Prionid

Subject:  NOISY BIG BROWN BEETLE
Geographic location of the bug:  New Portland Maine
Date: 07/26/2018
Time: 11:02 AM EDT
Your letter to the bugman:  Hi there! I was hoping you could give me a confirmation as to what in God’s name this guy is!!?? I saw it scurrying across the kitchen floor and almost lost my mind as initially I thought it was a cockroach but it didn’t move as fast and has a different body shape (this guy is more rounded, kind of shell-like and the wings are side by side not folded across the back like a roach).

I was able to put a paper cup over it and scoured the internet to find out what this  is.  I came across a click beetle, so turned it on it’s back to see if it made a “clicking” sound when it flipped back…it couldn’t flip over…it made a TON of noise though…like chirping/squeaking.

I rolled it back and covered it again.  Looked more and really I couldn’t find anything that matched, THEN  I  and found your site!  It’s FANTASTIC!  Within a few seconds I saw a picture of what I think I have here..  Brown Prionid. ..So other than a confirmation, I want to know if it’s a benign being and I should let it go on it’s way (outside of course) or a problematic intruder and  I should burn the house down and nuke the yard?  Oh, one more thing….are they capable of swimming?
Thanks a bunch!
How you want your letter signed:  Elise in Maine

Dear Elise,
Thanks for the compliment.  You are correct.  This is a Brown Prionid, and in our opinion, you should release it and not “burn the house down and nuke the yard,”  though that does make us chuckle and it reminds us of a response we once gave a reader, that “nothing short of a nuclear bomb will rid your property of all your dreaded insects.” 

According to BugGuide:  “Breeds in poles, roots(?) in contact with wet ground” meaning the larvae develop in rotting wood.  To the best of our knowledge, they do not infest homes nor do they trouble healthy trees, so in our opinion, they are benign.  Furthermore, these large beetles are a very nutritious source of food for many forms of wildlife.  They do not swim.

Letter 12 – Mating Brown Prionids

a photo for bug love?
Bug man,
You have helped me on many a quandry as to what I have discovered on porch screens late at night at my home. Recently I believe I’ve found a bug that does not regularly end up in Northeast Missouri.

They looked like mating Palo Verde Root Borers and were they ever big! I think the only reason I was able to find them was that they had stopped to get friendly in a lighted window. Sincerely,
Jessica Martin

Hi Jessica,
These look to us like mating Brown Prionids, Orthosoma brunneum. There are photos on BugGuide to match, and they are found in Missouri.

Letter 13 – Brown Prionid

Orthosoma brunneum?
Hello,
We found three of these around our home this evening, they are attracted to light and pretty much unafraid even when touched. They also shiver and make a strange sound something like a cricket but more unique.

My wife had a brief meltdown when she went online and saw a photo of an American cockroach – she was convinced that’s what we had and was ready to move! I had to become an amateur entomologist tonight using my camera, your site and other online resources. I think I can put her mind at ease- do you agree it is an Orthosoma brunneum?

This guy is 4.25 cm long and currently living in a jar with a gumdrop courtesy of my 2 1/2 year old daughter. (She named him buggy.) If you concur we’ll grant him compassionate release on the grounds that he’s no roach. Let us know! Great site, thanks for all your hard work, Sincerely,
Joe, Heidi and Hope in Hawthorne, NJ

Hi Joe, Heidi and Hope,
Your identification on the Brown Prionid, Orthosoma brunneum, is correct.

Letter 14 – Brown Prionid

what is it
I was just looking thru your site to try and identify this beetle I found tonight. It looks like the California long horn beetle. But I am in NH on vacation. Should I not release this insect. Is it not native to this area. I am sending the picture I took, but not very good since the beetle is in a vile for safe keeping until I hear that it is safe to release it.

We must confess that we were sure you had one of the Long-Horned Borer Beetles, but we were unsure of the genus and species. We asked Eric Eaton to try to clarify some identification points for us, which he did. However, in identifying your beetle, we now have an entirely new genus to consider.

Here is Eric’s response: “This appears to be a female Orthosoma brunneum, the Brown Prionid. Just what you needed, eh, another critter to get confused by:-) Ergates are large, western mountains mostly, with FINE teeth on the edge thorax. Derobrachus are HUGE, almost exclusively southwestern (though range throughout the souther tier of states I am told).

Prionus usually tend to be very squat, males with very thick antennae (almost comb-like or dentate in some species). An overall more robust critter than the others. Orthosoma is the most slender of all, and always a bright brown in color. Hope that helps, but getting Doug Yanega’s book on northeast longhorns would be your best bet (less than $20). Eric “

Letter 15 – Brown Prionid

Large Beetle found
Hi there, My wife found this beetle today (7/18/06) in the basement bathroom of our home in Rockfall, CT. It is the largest beetle (approximately 1 3⁄4” long) I have seen in or around here before.

We are just curious as to what it is called. It looks similar to a Paulo (?) root beetle but since we are in CT I’m not sure if it is. Well I hope you like the pictures! Thanks!
Aaron

Hi Aaron,
We believe this to be a Brown Prionid, Orthosoma brunneum, which has 11 antenna segments. It breeds in poles and roots in contact with wet ground. It was probably attracted to lights in your bathroom.

Letter 16 – Brown Prionid

bug question, duh
What the heck is the big guy?
molly

Hi Molly,
Labeling your photo “wedding and grad party” isn’t really what we had in mind when we put a request on our homepage for readers to provide us with location information on their submissions.

We prefer global location information since that is much more useful considering letters come to us from all over the world. The “duh” in your subject heading leads us to believe there might have been some intoxication involved at the wedding and graduation party, and we are thrilled there is an auto focus feature on modern cameras allowing even operators with a high blood alcohol level to take crisp clear photos like yours.

We hope the hangover has subsided. This is a Brown Prionid, Orthosoma brunneum. They are attracted to lights, which is probably the reason the small moth is hitch-hiking. They are found in moist locations in eastern North America. Eggs are laid in wood in contact with wet ground, including poles.

Letter 17 – Brown Prionid

I know you are busy but please help me!!!!!
Good morning,
Let me first say that I love your site and use it often. You recently saved the lives of the Golden Digger Wasps that are busy working in our yard. Now our two year old can play right next to there holes and we really don’t worry all that much. You have been very helpful to us and the little critters that live with us.

This morning though, I have become VERY uptight about somebody that was sitting in an empty wineglass on my counter. Please tell me this is NOT a roach, cause if it is, I am abandoning my home immediately.

He is huge, and quite quiet, not at all what I would imagine a roach would behave like.Can you ease my fears, please… Thanks so much,
Carla in Connecticut

Fear Not Carla,
This is not a roach. It is a Brown Prionid, Orthosoma brunneum. The larvae are wood borers and are usually found in poles and wood that is in contact with wet ground. We are also happy to hear your Golden Digger Wasps are alive and well.

Letter 18 – Brown Prionid

Some sort of beetle?
We just found your site…very cool! We are kind of bug people so it’s fun to see. I found this on the screen of the kitchen window. The light in the kitchen was on but I turned it off for the photo. It was around 10pm. Thanks,
Shadley

Hi Shadley,
This is a Brown Prionid, Orthosoma brunneum. This is one of the Longhorned Borer Beetles and the grubs feed in poles and roots that are in contact with wet ground.

Letter 19 – Brown Prionid

Orthosoma brunneum
I cam across your web site while trying to identify a caterpillar and fell in love. I check out your site almost every day I just can’t get enough of all the great pics and info. With my 7year old daughter being a bug fanatic we have had quite a few bug pet that we keep for a couple of days to watch and then let them go.

So when ever we find a new one we check here first. Anyway in search of identification on this one. I found him on my front porch at night by the light. We live in southwest PA. I believe it to be an Orthosoma brunneum. The one I found on your site you were not sure because of the pic so I hope my picture will help. Keep up the good work I’ll always be a viewer. Thanks
Mike

Hi Mike,
You are correct. Orthosoma burnneum is commonly called the Brown Prionid. We are thrilled to hear you and your daughter get such enjoyment from our website.

Letter 20 – Brown Prionid

Thu, Oct 9, 2008 at 4:18 AM
Hey Bugman, I love your site. It has been a favorite since we moved into our NJ home 4 yrs ago. I know you are quite busy, but I think this is a brown long horn beetle. Could you please tell me if is, and how menacing they are to our trees & gardens. I have noticed a number of giant stag horns also lately. Thank you in advance.
Cindy Lea
Plainfield, NJ

Hi Cindy,
You are correct, but more specifically, this is a Brown Prionid, Orthosoma brunneum. According to BugGuide, it “Breeds in poles, roots(?) in contact with wet ground. ” We would presume that the species is not a problem for healthy trees, but that it may become a problem if it breeds in support poles that are in contact with the ground. We doubt it is plentiful enough to cause you any concern.

Letter 21 – Brown Prionid

WTBettlebug?
Location:  South-central PA
July 26, 2010 8:31 am
I found this beetle? inside my house late at night, 7-25-2010. I live in a rural area with many trees and a stream. He is at least 30mm, mostly brown and has points off body, right behind the head. There are little ”feelers” around the mouth. Clear wingtips are sticking out at the end. I thank you for taking the time to look at my request.
Bethanne Schott

Hi Bethanne,
Your beetle is a Brown Prionid, Orthosoma brunneum, and it is found in the Eastern portion of North America.  BugGuide reports is as far west as Texas and indicates it “Breeds in poles, roots(?) in contact with wet ground.“

Letter 22 – Brown Prionid

California Root Borer???
Location:  Northeastern United States (Ohio, USA)
August 13, 2010 9:00 pm
Dear Bugman: This bug was on our screenhouse while we were camping in our home state of Ohio in the middle of July. From your photos it resembles the California Root Borer but we are a long way from there. This one also appears longer.

This was a big bugger about 2 1/4 inches long. At first glance before the pic was took it looked like it had silver drops for eyes along with the gold bands and we wondered if it had been eating radiation. I’ve seen many bugs in my day but not like this one.
Kathy (Ohio)

Hi Kathy,
For some reason, your entire digital file didn’t properly download and there are missing pixels that have cropped into this Brown Prionid’s abdomen.  Your observation that it looked similar to a California Root Borer is quite astute as they are both in the same tribe, Prionini. 

Your Brown Prionid is Orthosoma burnneum, and according to BugGuide it is found in moist forested areas from May to November.  Though there is an extended sighting period noted, most of the submissions of Giant Root Borers in the subfamily Prioninae, humorously referred to on BugGuide as “The Really Big Borers” come in July and August.

Hello Daniel,
Thanks for your quick response and thorough information. I’m sorry about the cropped pic. My son took the pic and IM’ed it to me. If I can get a better one from him, I will email it to you. My brother and I are very interested in bugs.

We have said that since our weather here in Ohio has been very hot and humid this summer and likened to the southern US climate that we may start to see insects indigenous to that area migrating up north. We feel this is an interesting concept and worth the watch. If I notice this then I will email you the info.
…
Kathy C. Seeman

Letter 23 – Brown Prionid

longhorn borer?
Location: alamo, tn.
June 22, 2011 11:26 am
If you have the time will you please give me the exact name of this beauty. I was sooo pleased to see him this morning. He was 2 inches in size. Thank you, beth light
Signature: beth light

Dear Beth,
We cannot help but to be overjoyed to read of your enthusiasm at this sighting and to read that you consider this magnificent beetle to be a “beauty”, but we couldn’t agree more.  It is a Brown Prionid, Orthosoma brunneum, and according to BugGuide it is found in moist forests in Eastern North America (Bugguide does indicate sightings in Texas) and it breeds in rotting wood found in contact with the ground.  Prionids are a subfamily of the Longhorned Borers.

Letter 24 – Brown Prionid

Orthosoma Brunneum-very cool looking beetle!
Location: Seymour, Tennessee (just south of Knoxville)
June 26, 2011 10:49 pm
Hello Bugman,
I know Brown Prionids like the one in this photo are pretty common, but if I do say so myself, this photo turned out so good and they look so cool, so I thought I’d share it with you. I hope you enjoy it! Thanks for all you do. You are awesome and I love coming back to your sight multiple times each day!
Signature: Michael Davis

Dear Michael,
Thanks for your compliment.  While we are more inclined to post rare and under-represented species on our site, we also love posting beautiful images of more common insects. 

The season is upon us for Prionid sightings, and the Brown Prionid is one of the most beautiful representatives from the group.  We also love your photograph.  The colors are stunning, and the cool green of the wall is a perfect background for the rich brown color of the beetle.

Letter 25 – Brown Prionid

Beetle in Vermont
Location: Saxtons River, VT
July 27, 2011 10:34 pm
Hi Daniel,
Wondering if you can identify this beetle? It was on my screen door tonight, in southeast Vermont. It was about 1.5” in length. Thanks!
Signature: K L Thalin

Dear K L Thalin,
This beautiful beetle is a Brown Prionid, Orthosoma brunneum, and it is one of a group known collectively at Root Borers.  If you would like to see more about this stunning creature, you can check out BugGuide.

Letter 26 – Brown Prionid

What kind of beetle is this?
Location: Granville, OH
August 15, 2011 11:44 am
Found on our deck in Ohio — bigger than other beetles we’ve seen.
Signature: Lisa Kelleher

Dear Lisa,
This magnificent beetle is known as a Brown Prionid, Orthosoma brunneum, and we have received a few identification requests for it this season.  According to BugGuide, it:  “Breeds in poles, roots(?) in contact with wet ground.”

Letter 27 – Brown Prionid

Subject: b
Location: Staten Island, NY
June 10, 2013 5:04 pm
Hi! I was hoping someone could positively identify this bug, and maybe provide some info on it. I think it might be a pine sawyer, but I’m not sure.
I found it inside my house in Staten Island, NY just as a long winter was finally ending. This was also after Hurricane Sandy hit our area pretty hard and it started to get cold…..
Is this a common insect around here? I’ve never seen one like it before.
Thanks!
Signature: -b

Dear b,
Like the Sawyers, this is a Longhorned Borer, but unlike the Sawyers, it is in the subfamily Prioninae, and we believe it is the Brown Prionid, Orthosoma brunneum.  Prionids are Root Borers that spend their larval stage “in poles, roots(?) in contact with wet ground” according to BugGuide, which also indicates: 

“Adults come to bait, so presumably take some rotting fruit, sap?”  They are a wide ranging eastern species and they are not considered to be rare, though they might be absent in some portions of their range due to a shortage of available food.

Hi Daniel!
Thank you for the response and information!
-brandon

Letter 28 – Brown Prionid

Subject: what is this?!
Location: philadelphia, pa
July 12, 2013 12:34 am
And idea what this is? Found it flying around my bedroom.
Signature: needs help!!

This is a Brown Prionid, Orthosoma burnneum, and adults are active during the summer months.  They are sometimes attracted to lights, and we suspect that is the reason it flew into your bedroom.

Letter 29 – Brown Prionid

Subject: bug
Location: western pa
July 26, 2013 10:36 pm
Found this bug outside on a wall on 7-26-13 temp was about 70 degrees
Signature: janet

Hi Janet,
This is a Brown Prionid, Orthosoma brunneum, and according to BugGuide, it:  “Breeds in poles, roots(?) in contact with wet ground.”

Letter 30 – Brown Prionid

Subject: Long-horned Beetle
Location: Central Massachusetts
July 7, 2014 10:41 pm
I saw this enormous thing late at night on my bean plants. It does not appear to have the markings or coloration of the Asian Longhorned beetle or the whitespotted sawyer beetle. It flew away while I was photographing it and landed too high for me to get better photos. It’s at least three inches long, not including it’s extremely long antennae.
Signature: Ellen P.

Hi Ellen,
This is one of the Longicorns in the subfamily Prioninae, but we are uncertain of the species because of the camera angle.  Our best guess is that this is a Brown Prionid, Orthosoma brunneum.

Letter 31 – Brown Prionid

Subject: beetle on screen door
Location: Princeton, NJ
July 25, 2014 7:21 pm
I found this guy hanging on my screen door in Princeton, NJ last night. Never seen one like it before! Some type of beetle, obviously. It’s about an inch and a half long, reddish-brown, with a orange stomach. Got any ideas?
Signature: Lynn

Dear Lynn,
It seems we have fielded more than the usual number of Brown Prionid, Orthosoma brunneum, identifications this summer.

Letter 32 – Brown Prionid

Subject: brown beetle?
Location: currently in IL, but not where it came from
July 27, 2014 10:40 am
We just returned from a two week trip that took us through Illinois, Indiana, Ohio, Pennsylvania, Maryland, Virginia, North Carolina, West Virginia, and Kentucky. It was hot and humid, with a few big storms that rolled through. When we got home, this bug was in our van.

It is about two inches in length, not including the antennae, which add another inch (if pulled straight). It flies and seems attracted to light. Wondering what it is. We live in central IL and aren’t comfortable with just letting it go, without knowing if it’ll cause harm.
If we can’t let it go back into the wild, then we need to know what it is so we can care for it. Thank you!
Signature: Heather

Dear Heather,
We have received more than the usual number of Brown Prionid, Orthosoma brunneum, identification requests from eastern North America this summer.  According to BugGuide, Illinois is well within the sighting range of the species, which is native.  Local populations may vary from place to place within the range.

Letter 33 – Brown Prionid

Subject: What is this?
Location: Central New Jersey
August 3, 2014 8:13 pm
We found this bug in our house upon returning from vacation. It was just lying on the floor in our family room. We were glad that it was already dead and we weren’t here when it entered.

Neighbors have mentioned finding similar ones in the neighborhood, but no one seems to have seen them before this year. Seems to look like a lot of other beetles out there, but the tail stinger is throwing us off.
Signature: Jeanette

Hi Jeanette,
It seems like this year we have gotten a few more reports of Brown Prionids, Orthosoma brunneum, than we have in previous years, but mid summer is the peak time for sightings of this species and its relatives.  What you have mistaken for a stinger is the ovipositor of the female, an organ used to lay eggs.

Letter 34 – Brown Prionid

Subject: Caught by our cat
Location: NW Wisconsin
August 12, 2014 2:53 pm
This bug was hiding in the sunroom INSIDE the house, cornered by the cat. The bug was aggressive and actually squeaked when confronted. Very large, two inch range. Sorry, the dead body is gone. But, we have a picture. Looking forward to any guesses. Thanks, Keith
Signature: Keith

Hi Keith,
This impressive beetle is a Brown Prionid, Orthosoma brunneum, and while we tend to get a few submissions of Brown Prionids each summer, we have had a significantly greater numer this summer. 

The larvae are wood borers and according to BugGuide:  “Breeds in poles, roots(?) in contact with wet ground.”  We suspect this individual was attracted to your house because of lights.

Letter 35 – Brown Prionid

Subject: Roach
Location: Pennsylvania
July 13, 2015 2:26 pm
Hello. I saw this bug on the outside of glass French door the other morning. Now I found him or his buddy under the wheel of the grill on deck, which is located a short distance from French doors. I am watching him now he’s slowly moving back under the grill wheel. Boy I hope it’s not a roach! He’s about 2 inches long
Signature: Heather

Dear Heather,
This is not a roach.  This impressive beetle is a Brown Prionid, Orthosoma brunneum.

Letter 36 – Brown Prionid

Subject: Brown Prionus Beetle?
Location: Troy, VA
July 9, 2016 8:56 am
This large and impressive beetle was on my screen last night. I’m guessing it’s a prionus beetle.
Thanks for your help.
Signature: Grace Pedalino

Dear Grace,
This is NOT a Brown Prionus, but it is a Brown Prionid, and hopefully we will be able to properly explain the difference.  All living organisms on our planet are classified by an increasingly more specific categorization, beginning with the Kingdom, which in this case is Animal, and ending with a species designation of a lower case name following the genus, and forming the binomial that ensures that each creature is recognized as a distinct species worldwide. 

It should be noted that a subspecies name may follow the species name, in which case the subspecies will have a trinomial, three-part name.  Your beetle’s binomial genus/species name is Orthosoma brunneum and it is commonly known as the Brown Prionid. 

A Prionid is a Longhorned Borer Beetle that is classified in the subfamily Prioninae, and that subfamily also includes beetles in the genus Prionus.  So the genus Prionus and the genus Orthosoma are both in the subfamily Prioninae and their members collectively can be called the Prionids. 

Letter 37 – Brown Prionid

Subject: What is this??
Location: Western PA
July 17, 2016 10:50 am
Found this bug on the side of my couch and cannot identify it. It’s reddish brown in color and about 3 inches long. From the western Pennsylvania area. Can you help?
Signature: Nicole

Dear Nicole,
We suspect this Brown Prionid entered your home after being attracted to lights.

Letter 38 – Brown Prionid

Subject: This doesn’t look like a PA native
Location: Pennsylvania
July 22, 2016 9:46 pm
About 1-1/2″ long. We didn’t spend much time together, he was quickly relocated to the great outdoors. This is in Pennsylvania.
Signature: Christine

Dear Christine,
The Brown Prionid, Orthosoma brunneum, is a native species in Pennsylvania.

Letter 39 – Brown Prionids

Subject: beatle/cockroach looking monstrosity
Location: northern new jersey suburbs
July 25, 2016 1:10 pm
Dear bugman,
Hello old sport was wondering if you could help me I.d. this scoundrel. Only have seen them at night, mostly seen flying into my garage from the outside. My brother says they fly sort of upright rather than parallel to the ground. Summer time in Northern New Jersey Suburbia. Checked numerous bug data bases of new jersey insects and came up empty handed. Thanks!
Signature: Gene Jefferson

Dear Gene,
These are Brown Prionids, Orthosoma brunneum, and according to BugGuide:  “Breeds in poles, roots(?) in contact with wet ground” so they may be emerging from dead stumps you have in the vicinity.  They are also attracted to lights.  We are tagging this posting as Unnecessary Carnage as these two Brown Prionids do not look like they died of natural causes.

Letter 40 – Brown Prionid

Subject: BIG ONE
Location: Northern NJ
July 26, 2016 8:14 pm
Please tell me what this is! I have found 2 so far in my kitchen… July in NJ. They don’t seem to be doing anything wrong but they are so big! I would like to know if they are dangerous in any way. Thank you so much!
Signature: TB

Dear TB,
Though we always get reports of Brown Prionids each summer, this year there seems to be more than the usual number of sightings.  We suspect they are being attracted to your kitchen because of lights at night.

Letter 41 – Probably Brown Prionid

Subject: I’d large flying beetle-like insect which could be a hornet
Location: Tennessee
June 7, 2017 10:12 am
Flying at night. Loud. Black until opens wings, revealing a solid orange torso. Is this a hornet? Twice larger and thinner than any hornet I’ve seen.
Signature: Connie

Dear Connie,
This is NOT a hornet.  It is a Longhorned Borer Beetle in the family Cerambycidae, and though your image lacks critical sharpness, it appears to be a Brown Prionid.  More images are available on BugGuide.

Letter 42 – Brown Prionid

Subject: what insect is this?
Location: westmoreland county Pennsylvania
July 6, 2017 1:28 pm
Curious as to what insect this is
Signature: Don Kirkland

Dear Don,
This is a Brown Prionid, a common summer identification request for our site.

Letter 43 – Brown Prionid

Subject: Bug
Location: Gays mills wis
July 13, 2017 11:14 am
Wondering what this is? Found outside on a rock near our pool
Signature: Brenda

Dear Brenda,
Comparing your image to this Bugguide image, this looks like a Brown Prionid to us.  According to BugGuide:  “Light brown, sides of elytra parallel. 11-segmented antennae, rounded, never flattened.”  Based on BugGuide data, Wisconsin is about the westernmost range of the Brown Prionid in the northern portions of North America.

Letter 44 – Brown Prionid

Subject: Large beetle in Pa!
Location: Northeastern Pennsylvania
July 15, 2017 7:23 pm
Hello!! I have never seen this bug in Pennsylvania before! It was a humid summer evening, and I noticed it on my outside screen. Nearly 2″ long it’s body alone, it made a squeaky kind of noise when it walked away from us on the ground. Took this picture as it was on the ground. What is this bug??
Signature: Debbie

Dear Debbie,
This impressive beetle is a Brown Prionid.  The squeaking you heard is called stridulation.  The beetle makes the sound by rubbing parts of its body together.

Letter 45 – Brown Prionid

Subject: Blister Beetle?
Location: Poughkeepsie, NY
July 25, 2017 5:48 am
Is the beetle in the attachment some sort of blister beetle? What is it?
Signature: Dave Jemiolo

Dear Dave,
This is not a Blister Beetle, and we do not believe any Blister Beetles attain this size.  This is a Brown Prionid, one of the Root Borers in the subfamily Prioninae.  According to BugGuide:  “Breeds in poles, roots(?) in contact with wet ground.”

Letter 46 – Brown Prionid

Subject:  this guy whacked me in the head
Geographic location of the bug:  Maine usa
Date: 07/17/2018
Time: 03:31 AM EDT
Your letter to the bugman:  Just curious I see this type of bug often.. took me a while to get the courage to put him back outside
How you want your letter signed:  brooke

Dear Brooke,
This impressive Longicorn is a Brown Prionid.  According to BugGuide:  “Adults come to bait, so presumably take some rotting fruit, sap?”

Letter 47 – Brown Prionid

Subject:  Large beetle
Geographic location of the bug:  Cape Cod, MA
Date: 07/27/2018
Time: 09:20 AM EDT
Your letter to the bugman:  I found this guy on my car this morning. I thought it was a June bug at first, but now I’m not so sure.
How you want your letter signed:  Donna

Dear Donna,
We just finished posting another image of a Brown Prionid.

Letter 48 – Brown Prionid

Subject:  What’s that bug?
Geographic location of the bug:  Avon, NY
Date: 08/10/2019
Time: 01:43 PM EDT
Your letter to the bugman:  Found it at night on our patio. About 2.5 inches long. Wings covered with brown somewhat  translucent hard shells. Moving vigorously around,  non aggressive. We moved it carefully to nearby meadow. What is this bug? Many thanks to whomever can give us a clue.
How you want your letter signed:  Nature lover.

Dear Nature Lover,
Orthosoma brunneum which is pictured on BugGuide is commonly called a Brown Prionid.

Letter 49 – Prionid from South Africa

Subject: Brown SA beetle
Location: Waterberg mountains, South Africa
November 26, 2015 5:54 am
The images of this brown beetle was taken in the Mabalingwe game reserve in the Waterberg mountains two hours north of Johannesburg, South Africa.
It may not look pretty but it does seem to have unusually serrated antennae. I wondered what it is?
Signature: Dave Smith

Dear Dave,
Your Longhorned Borer Beetle from the family Cerambycidae is a Prionid in the subfamily Prioninae, but we cannot provide a species name at this time.  There are many species pictured on iSpot.

Letter 50 – Prionid from Tanzania

Subject: Identification Request
Location: East Africa
January 19, 2017 7:28 pm
Hi there,
Here are a few interesting ‘bugs’ I photographed while living in Tanzania between 2008 and 2011. Hoping you can help me (finally) identify exactly what they are 🙂
Many thanks
IMG 8969 in Longido, Northern Tanzania (found dead)
Tom

Dear Tom,
This is one of the Longicorns from the family Cerambycidae, and it is one of the Root Borers in the subfamily Prioninae.  Based on this FlickR posting, it might be in the genus Tithoes, however it does not resemble others from that genus on our site. 

Based on The Old World Cerambycidae Search, it appears to be Anthracocentrus beringei, but searching that name does not provide any additional information.  While we cannot with certainty provide you with a species, we are nonetheless confident it is a member of the subfamily Prioninae.   

Letter 51 – Prionid from Thailand

Subject:  I.D. of a Very Irritated Bug
Geographic location of the bug:  Thailand
Date: 09/15/2017
Time: 02:45 AM EDT
Greetings! If you could I.D. the attached bug, I would deeply appreciate it, as these manaical carnivores are rampaging throughout my house! I stuffed one in a jar, and it ate an entire snack bag of sweet pork jerky. I’m afraid I’m next on the menu. Thank you in advance for your efforts.
How you want your letter signed:  Suzanne Jamsrisai

Dear Suzanne,
This is a Prionid in the subfamily Prioninae.  It resembles Dorysthenes (Paraphrus) granulosus which we found on the World Wide Cerambycoidea site.  They are not maniacal carnivores, though the mandibles of large individuals might deliver a painful bite.

Letter 52 – Prionid Grub

Subject: Big Ol’ Larva – Carpenterworm?
Location: Raymond, California (Sierra foothills)
October 29, 2012 4:03 pm
We were splitting wood this weekend, and found this large larva inside one of the interior live oak rounds. We believe it to be a carpenterworm larva – can you confirm?

As you can imagine, it was not happy to have been revealed to the world, so our size comparison with the measuring tape isn’t quite in alignment.
Love your website!
Thanks so much
Signature: Megan Ralph

Hi Megan,
This is the grub of one of the Longhorned Borer Beetles, most likely a Prionid, and possibly the California Prionus.  See this image from BugGuide for comparison.  According to BugGuide: 

“Larva feed primarily on living deciduous trees (oaks, madrone, cottonwood) and are also recorded from roots of vines, grasses, and decomposing hardwoods and conifers. Will also attack fruit trees growing on light, well-drained soils (e.g. apple, cherry, peach)”

Letter 53 – Prionid Larva

Subject:  Grub
Geographic location of the bug:  San Diego coastal 15″ below ground
Date: 01/20/2018
Time: 08:00 PM EDT
Your letter to the bugman:  I’ve never encountered a grub so large before and would like to know what kind of beetle this will become.
How you want your letter signed:  Matt Lee

Dear Matt,
This appears to be one of the Root Borers in the subfamily Prioninae.  Was there a tree or shrub nearby, or perhaps the trunk of something that had died?  While we are reluctant to provide a definitive species identification, it might be the larva of a California Root Borer like this image posted to BugGuide. 

According to BugGuide:  “Larvae: Up to 80mm long” and “Larva feed primarily on living deciduous trees (oaks, madrone, cottonwood) and are also recorded from roots of vines, grasses, and decomposing hardwoods and conifers. Will also attack fruit trees growing on light, well-drained soils (e.g. apple, cherry, peach).” 

If that is a correct identification, here is an image of an adult male California Root Borer, though your larva might belong to a different, though similarly large Prionid with long antennae. 

Letter 54 – Prionid Root Borer

SC beetle
I live on Hilton Head Island, South Carolina. I just saw this bug out on my back porch. I cannot find anything on the internet about it. I have never seen it before. It is about 2 inches long not including the antenna. Can you please tell me what it is? Thank you!
Sarah Hurst

Hi Sarah,
Your really big beetle is one of the Prionid Root Borers. We suspect it is Prionus imbricornis, the Tile Horned Prionus, but we would like Eric Eaton to confirm that identification.

Letter 55 – Prionid from Thailand, Probably Dorysthenes (Paraphrus) granulosus

Subject: Thai longicorn
Location: North of the Gulf of Thailand
April 9, 2017 8:40 pm
Hi, I found this longicorn at night at the start of the hot season (March) in central Thailand, right before two weeks of heavy rain showers.
It was about 8cm in length and I was able to pick it up, it did not hiss or squirm but may possibly have been dazed by a light.

The area where I found it is a small open grassy area, at the side of a reservoir and wetland, surrounded by protected tropical forest, not far from Chonburi on the coast of the Gulf of Thailand.

A week before finding this specimen, I saw the same species mating on a wall, and another drowned in a small puddle of water. Since March I have not seen any so possibly they were active to mate?
It would be awesome if I could get an ID!
Signature: Laura

Dear Laura,
Your Longicorn is a Prionid in the subfamily Prioninae.  Prioninae of the World has a page devoted to species found in Thailand, but not all species are pictured. 

Of the ones pictured on Prioninae of the World, in our opinion, the one that most resembles your individual is Spinimegopis lividipennis because both have several prominent spines on the thorax.  The species is also pictured on Cerambycoidea Forum.

Update:  April 29, 2017
Thanks to a comment from Tina, we agree that Dorysthenes (Paraphrus) granulosus which is pictured on FlickR and on Coleoptera Atlas appears to me a very good possibility for a species identification.

Letter 56 – Sudanese Prionid Borer

Serious mandibles
hello bugman.
I sent you some photos the other day but you must be busy cause I havent seen them. They were mostly just pretty pics. I have a question about this critter. He is about 3-4 inches long and has these great big jaws.

Quite placid when he is still but if you touch his back, he spins around ready to attack. Is like a off brown with light brown mottled color markings. Quite agressive.

We are in the desert in Sudan and have plenty blister beetles, and awesome moths, one I ID from your site being the white lined sphinx. Thank you! Thanks for a very interesting site!
Marc B. Potgieter
Khor Abeche
Southern Darfur
Sudan

Hi Marc,
Our mail volume is so heavy right now, we could not answer every letter if we spent 24 hours a day on the site. We choose letters at random. This is some species of Prionid Borer. It resembles the North American Derobrachus species.

The heavy mandibles are necessary as the large grubs are wood borers, often in roots. The adult needs to chew its way to the surface through the wood after it emerges from the pupa.

Letter 57 – Unidentified Prionid from Washington

Subject:  Weird bug found at work
Geographic location of the bug:  Grays harbor washington
Date: 08/11/2021
Time: 06:14 PM EDT
Your letter to the bugman:  Found this bug while I was at work and it’s massive, was probably 2 1/2 almost 3 inches. kinda think it’s a June bug but it doesn’t got the stripes
How you want your letter signed :  What is it?

We are only able to provide you with a partial identification on your discovery.  This is a Longhorned Borer Beetle in the family Cerambycidae, and it is a member of the subfamily Prioninae, the Root Borers.  Unfortunately we are unable to provide you with a species name. 

Though you submitted three images, one was a red rectangle and one a black rectangle with no insects visible.  The image we posted has many identifying features hidden in the grass. 

The gray coloration and lack of thoracic spines are distinctive, but it doesn’t look like any of the species on BugGuide.  Is Grays Harbor a town that gets international ships?  Perhaps one of our readers with more experience will be able to provide a species identification. 

Sorry it wouldn’t let me put anymore pictures on because there wasn’t enough space for 2 pictures but I do have a video and we just got a storage container from China at my work like 4 months ago.

Letter 58 – Who left the Head of a Prionid Beetle on Kerri’s Deck???

Should this even be in New Hampshire?!
Location: New hampshire
June 30, 2011 6:29 pm
This little creature made his way onto my deck last night, as to where he came from or his name that unforuntaly wasnt attached to him.. Im questioning if this should even be in new hampshire, i have never see anything like it!
Signature: Kerri

Dear Kerri,
We feel like we have been involved in a Sherlock Holmes novel or a CSI episode.  This is the head of a Prionid Beetle, and there are numerous species that might be encountered in New Hampshire.  Our most likely subject is a male Broad Necked Root Borer, Prionus laticollis, which is pictured in our archives and on BugGuide where it is indicated that:  “Antennae have 12-13 segments.” 

The head you found appears to have 12 segments on the antennae.  The big question is how did that head get on your deck.  Birds will sometimes eat fatty insects, and the body of a Prionid Borer is full of fat, and the head hasn’t much nutritional value, not to mention it is harder and less palatable.   BugGuide also indicates:  “Males are attracted to lights.” 

This is a male as females have much less developed antennae.  If this Prionid was attracted to a light and your house cat encountered it, perhaps the cat ate the body of the insect and left you the head as a trophy.  The predator will have to remain a mystery.