Iron Cross Blister Beetle: Essential Guide for Curious Minds

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The Iron Cross Blister Beetle is an intriguing insect, recognizable by its striking appearance and unique defensive mechanism.

Scientifically known as Tegrodera aloga, this beetle belongs to the Meloidae family, which features other blister beetles as well.

They are known for their distinctive markings: a bright red or orange cross pattern on a dark, usually black, background.

Iron Cross Blister Beetles Mating

These beetles have an interesting defense strategy to protect themselves from predators.

When threatened, they release an odorless, colorless secretion called cantharidin. This substance is a potent toxin causing irritation, blisters, and can even be life-threatening for some animals.

These beetles inhabit dry areas and are typically found west of Arizona.

They can be found in various regions of North America, including parts of the US and Central America.

Specifically, they are prevalent in Arizona and also found in California and Sonora.

Their habitat primarily consists of grassy areas and flowering plants, where they are attracted to nectar and various flowers.

It’s essential to approach these beetles with caution due to their toxic secretion, especially when encountered in a garden or outdoor setting.

Iron Cross Blister Beetle Identification

Physical Characteristics

The Iron Cross Blister Beetle is a species known for its distinctive physical traits.

It is a medium-sized beetle with a bright red head, yellow-orange body, and black legs.

Its name comes from the dark cross-shaped markings on their wings.

Iron Cross Blister Beetle

The beetle’s body is mostly black, which contrasts with the red head and prominent black cross on their wing covers.

This distinct coloration makes them easily identifiable among other beetles.

This beetle has:

  • A soft, leathery body
  • A wide head
  • Narrow thorax
  • Large, prominent eyes

The head and thorax are wider than the visible abdomen.

Their wings don’t cover the abdomen tip completely, and their front wings are shorter compared to other blister beetles.

Biology and Life Cycle

Eggs and Larval Stage

  • The female Iron Cross Blister Beetles lay their eggs in shallow cavities in the soil during summer.
  • First instar larvae feed on the eggs of grasshoppers or bee nests.

Pupa and Adult Stage

  • Blister beetles spend winter in the larval stage and pupate in spring.
  • Adult blister beetles, such as the striped blister beetle, Epicauta vittata, emerge in early summer, with body lengths ranging between 1/3 to 2/3 inches long1.
  • During daytime, adults feed on plant parts and mate.
  • Females lay eggs again after mating, completing their one generation per year life cycle2.

Comparison table:

Stage Duration Activity
Egg Summer Laid by females in soil cavities
Larva Winter Feeding on grasshopper eggs or bee nests
Pupa Spring Development within a protective casing
Adult Early Summer Feeding on plants, mating, and laying eggs for next cycle

Distribution and Habitat

North America

The Iron Cross Blister Beetle can be found in various regions of North America, including parts of the US and Canada. Some specific states where it is prevalent include Arizona and Florida.

Central America

In Central America, the Iron Cross Blister Beetle is commonly found in countries such as Mexico. It inhabits parts of the Sonoran Desert, which spans across the US-Mexico border.

Specific Regions

  • The Sonoran Desert covers parts of Arizona, Sonora, and Mexico.
  • In the US, these beetles can be found in states such as Arizona and Florida.

The Iron Cross Blister Beetle can adapt to various habitats, including grasslands and agricultural fields where it feeds on different flowering plants.

Iron Cross Blister Beetle

Diet and Feeding Habits

Floral Preferences

The Iron Cross Blister Beetle is known for its attraction to certain flowers and plants. They are mainly found feeding on leaves, pollen, and nectar from blooms of alfalfa and other flowering plants.

  • Examples of floral preferences:
    • Alfalfa
    • Aster flowers
    • Goldenrod

Below is a comparison table between the two most common plants on which these beetles feed:

Plant Leaves Pollen Nectar
Alfalfa Yes Yes Yes
Aster Yes Yes Yes

Insect Predation

In addition to consuming plant material, the Iron Cross Blister Beetle is also known to prey on insects, particularly grasshoppers.

This makes it beneficial for reducing grasshopper populations in some agricultural settings.

Effects of Cantharidin

Impact on Humans

Cantharidin, a toxic chemical produced by iron cross blister beetles, can cause several health issues in humans when they come into contact with it:

  • Blisters: Direct contact with the beetles or their secretions can lead to blisters on the skin and painful inflammation1.
  • Digestive tract problems: Ingesting cantharidin can cause severe damage to the urinary tract and gastrointestinal lining2.
  • Eye irritation: If cantharidin enters the eyes, it can lead to pain and severe irritation.
Iron Cross Blister Beetle

Impact on Animals

Cantharidin is toxic to various animals, especially when ingested. Effects include:

  • Pests: As a defense mechanism against predators, cantharidin can be lethal to a wide range of pests1.
  • Wildlife: Animals like birds or small mammals can suffer from poisoning if they feed on iron cross blister beetles1.

Impact on Livestock

Livestock, particularly horses, are susceptible to cantharidin poisoning. Ingestion of beetles can result in numerous health issues and even death1:

  • Digestive disorders: Horses ingesting cantharidin may experience colic, diarrhea, and inflammation1.
  • Sweating: Affected animals exhibit excessive sweating1.
  • Shocks: In severe cases, cantharidin can lead to shock and even death1.

Comparison of Cantharidin’s Impact on Humans, Animals, and Livestock:

Interactions with Other Species

Predators and Prey

The Iron Cross Blister Beetle (Tegrodera aloga) belongs to the Meloidae family. These beetles have a variety of predators, including lacewings and birds.

They are also prey for other insects, such as parasitic wasps.

Influence on Gardens and Crops

Iron Cross Blister Beetles can be a garden pest, causing damage to crops like potatoes, tomatoes, beans, and clover.

Iron Cross Blister Beetle

Some examples of their impact on common garden plants include:

  • Potatoes: beetle feeding damages leaves, reduces yield
  • Tomatoes: can damage foliage, weaken plant structure
  • Beans: defoliation of bean plants, affecting growth
  • Clover: feeding on leaves causes disruption in legume growth

Comparison table of Iron Cross Blister Beetle’s impact on gardens and crops:

Crops Damage caused by the beetle Severity of impact
Potatoes Damages leaves, reduces yield Moderate to Severe
Tomatoes Foliage damage, weakens structure Moderate
Beans Defoliation, affects growth Moderate
Clover Feeding on leaves, disrupts growth Moderate

Control and Prevention Methods

Personal Protective Measures

  • Wear gloves: Iron cross blister beetles contain a toxic substance called cantharidin. Wearing gloves can protect your hands from direct skin contact.
  • Be cautious: Handle beetles carefully if needed to avoid accidentally crushing them and releasing toxins.

Agricultural and Garden Techniques

  • Soapy water: Submerge the beetles in a bucket of soapy water as an effective method of controlling them.
  • Diatomaceous earth: Sprinkle diatomaceous earth around plants to deter beetles from coming in contact with them.
  • Row covers: Using row covers can help protect your plants from the beetles without using chemicals.
  • Biopesticide: Applying a biopesticide containing beneficial organisms, such as Beauveria bassiana, can help control blister beetle populations.
Method Pros Cons
Soapy water Non-toxic, eco-friendly Manual process, time-consuming
Diatomaceous earth Safe for beneficial insects, non-toxic Requires reapplication, can be messy
Row covers Chemical-free, physical barrier May not be suitable for large-scale use
Biopesticide Targets specific pests, eco-friendly Limited availability, may affect non-target insects

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?

Iron Cross Blister Beetle


The Iron Cross Blister Beetle, scientifically termed Tegrodera aloga, stands out with its vibrant cross pattern against a dark backdrop.

A member of the Meloidae family, this beetle has a unique defense mechanism, releasing the toxin cantharidin when threatened.

These beetles inhabit dry areas and are typically found west of Arizona.

While their appearance is captivating, caution is advised due to the potential harm from their toxic secretion, especially in gardens or agricultural settings.


  1. Blister Beetle – Texas A&M University 2 3 4 5 6 7 8 9
  2. Blister Beetles and Alfalfa | Oklahoma State University 2

Reader Emails

Over the years, our website, has received hundreds of letters and some interesting images asking us about iron cross bliser beetles. Scroll down to have a look at some of them.

Letter 1 – Iron Cross Blister Beetle

red headed yellow winged?
Location: Phoenix, AZ
April 22, 2011 11:48 pm
I saw this bug walking across the parking lot at my wife’s work.. We live in Phoenix, AZ.. It had 6 legs. I thought it looked like a giant red ant. Thanks for any and all info you have on it.
Signature: Ben

Iron Cross Blister Beetle

Dear Ben,
This is an Iron Cross Blister Beetle, and each spring we get several identification requests from their range in California and Arizona. 

Your letter is our first report for 2011, though we did receive one report in December 2010 that is most likely due to the unusual weather pattern and unseasonal rains since late 2010. 

All Blister Beetles should be handled with care as they are able to secrete a compound known as cantharidin that can cause skin to blister.

Letter 2 – Iron Cross Blister Beetle

Iron Cross Blister Beetle
Location: Chandler, AZ
May 12, 2011 9:27 pm
We saw this most beautiful bug today on our garage door. I think it’s an Iron Cross Blister Beetle. Just wanted to share the photo with you.
Love your web site!
Signature: Mary

Iron Cross Blister Beetle

Dear Mary,
Each year around this time we receive several requests to identify Iron Cross Blister Beetles that are seen in Arizona and California. 

We are happy you were able to self identify since we are currently totally bogged down with identification requests that we will never be able to fulfill.

Letter 3 – Iron Cross Blister Beetles

Invasion of the Thunder Bugs
Thu, Apr 30, 2009 at 8:01 PM
My cousin and I were riding our bikes through our subdivision in Arizona when we noticed a huge congregation of these red, yellow, and black bugs on the sidewalk next to a construction sit. It was more toward the middle of August and about 98 degrees F*.

They were pretty big, 1.3 – 2 inches long, and quite fierce looking (their coloring reminded us of a thunder/firestorm), although, even with the ultra efficient-looking wings, they didn’t fly when we came near and were actually a bit sluggish.

We did want to touch them, but, quite content with our bite-free, scratch-free, sting-free hands, we ultimately settled for a photograph. So, to cut a long story in a concise little request: we were sort of hoping you could help us identify them?
Andy and Chipi

Iron Cross Blister Beetles
Iron Cross Blister Beetles

Dear Andy and Chipi,
Every once in a while we receive a photo that we consider spectacular. We absolutely love your photo of Iron Cross Blister Beetles. These flashy beetles make appearances in Arizona and California in the spring. 

While handling Iron Cross Blister Beetles, or any other Blister Beetles for that matter, would probably not result in bites, scratches or stings, there is a very good chance it might result in blisters since the beetles secrete a substance known as cantharidin, the blistering agent.  It is also the legendary Spanish Fly, the aphrodesiac made from ground Blister Beetles.

Letter 4 – Iron Cross Blister Beetle

It’s big but what is it?
I’m out in the field in the southern Owens Valley, east of the Sierra Nevada in California, at about 4600′, and without reference materials. I’ve run across this insect that I can’t recall seeing before, but it’s fairly large (c. 3 cm in length), so

I’m surprised that I’ve not noticed it before and I’m really curious about it. See attached photo. It, and several of it’s brethren, are crawling about rather clumsily on some phlox-like flowers. Can someone identify it for me? Thank you,

Hi Jan,
This is an Iron Cross Blister Beetle in the genus Tegrodera.

Letter 5 – Iron Cross Blister Beetle

it fly’s
from tucson arizona. there are very many of these insects outside my house. please tell me.

Hi Mikie,
We haven’t gotten a photo of one of these for years. Your little beauty is a member of the Blister Beetle Family known as Iron Cross Blister Beetle, Tegrodera latecincta.

Letter 6 – Iron Cross Blister Beetle

Do you know what kind of bug is in the attached photo?
Hi, Do you know what kind of bug is in the attached photo? I found him in my yard. By the way, we let bugs – no carnage here. Your thoughts…

Hi Rita,
This is an Iron Cross Blister Beetle in the genus Tegrodera. There are at least two similar looking species with the same common name, and your specimen looks like Tegrodera erosa. Tegrodera latecincta has a more defined black cross pattern on the elytra or wing covers. There is a third species and they are found in the lower Sonoran Desert where adults feed on blossoms.

Letter 7 – Iron Cross Blister Beetle

Soldier Beetles
I recently visited your site to find out what kind of bug was in my backyard. Today I have seen at least 30-40 soldier beetles. ( I know what they are because of info and pictures on your site.)

I took some pictures of them, and have attached one because they are large files. Wanted to contribute since your site helped me figure it out. Do you know if they are harmful to cats and dogs? Just concerned because my animals play in the backyard.
Queen Creek, AZ

Hi Jo,
Somehow you have misidentified your beetle. This is not a Soldier Beetle but an Iron Cross Blister Beetle, Tegrodera latecincta. Blister Beetles contain a chemical, cantharidin, which can cause blisters on human skin. It is more of an irritant than a dangerous poison. If your cats and dogs try to eat them, they will probably have a severely irritated mouth.

Letter 8 – Iron Cross Blister Beetle

What is this bug?
This bug is just over an inch long, and I can’t find it in any of my or the library’s insect ID books.
Nick Johnson

Hi Nick,
Your letter is the fourth this week requestion an identification for the Iron Cross Blister Beetle.

Letter 9 – Iron Cross Blister Beetle

Blister Beetle
Hi bugman,
I found this guy swimming in my pool today with my kids. His colors were so beautiful and vibrant that I had to figure out what he was. I have been in Arizona my entire life and have never seen a beetle like this. Of course the kids freaked and demanded that I kill right away.

I instead gently swept the guy out the water and let him dry off. He was a very good and let me snap more 20 pictures. I have attached the better ones. I started googling for +beetle “red head” “yellow wings” “black spots” and some other variations and viola, I got to your site. However, I scared to learn that this bug is actually poisonous. Can it hurt my dog or cat? Thanks,

Hi Jeff,
Thank you for sending in your great photos of an Iron Cross Blister Beetle, Tegrodera latecincta. Blister Beetles contain a chemical, cantharidin, which can cause blisters on human skin. It is more of an irritant than a dangerous poison. In Arizona, scorpions, black widows and rattlesnakes are a greater threat to you and your pets. In the scheme of things, an unfortunate encounter with a Blister Beetle would be an inconvenience.

Letter 10 – Iron Cross Blister Beetle

different variety of Tegrodera
Found in my yard in the Owens Valley (Lone Pine), elev. 4600′, striding about quite purposefully and fearlessly. According to,
this is the true Tegrodera latecincta:

“The third and northernmost species is T. latecincta Horn, known from the Antelope and Owens valleys. ” Whereas the photos you have already posted are of Tegrodera aloga, according to the above reference. About 1.5″ long. Be all that as it may, thanks for a great site!

Thanks for the photo, information, link and correction. This is an excellent example of when location is critical for exact species identification.

Letter 11 – Iron Cross Blister Beetle

Odd insect in Saguaro Park
Dear WTB,
I took this in Saguaro National Park today, thought the pattern on the wings was unusual…any ideas?
cd krall

Hi CD,
You have taken a most awesome photo of a most awesome insect, the Iron Cross Blister Beetle in the genus Tegrodera. Your photo has the aesthetic of a safari photo of a large animal. There are several possible species, including Tegrodera aloga which is not represented on BugGuide.

Letter 12 – Iron Cross Blister Beetle

Red-headed bug with yellow spotted wings found in AZ desert
April 15, 2010
There were a whole bunch of these clinging to low plants in the parking lot at Phoenix Int’l Raceway. They were not very aggressive, but a couple did try to crawl on people, and they didn’t seem to fly. They were all gone when we returned to the truck in the dark about 10 hours later.
AZ Desert – SW Valley

Iron Cross Blister Beetle

Dear Paula,
Your Iron Cross Blister Beetle is found in Arizona and California in desert areas.

Letter 13 – Iron Cross Blister Beetle

Red Ant-like bug with yellow wings?
April 25, 2010
Hi! My husband and I were out to lunch and when I got out of the car I saw this bug. It was crawling on the pavement around the tire of my car. It was pretty fast and it kept moving around the tire. It looks almost like a large red ant with yellow wings.

We live in Arizona, it is April and about 80 degrees. We have never seen anything like it. It is about an inch long and we did not see it fly. I am just dying to find out what it is and anything about it!? Thank you!
Very Curious
Phoenix, Arizona

Iron Cross Blister Beetle

Dear Very Curious,
You encountered an Iron Cross Blister Beetle in the genus Tegrodera.  BugGuide reports them from California and Arizona and indicates that they are found:  “In the lower Sonoran desert, T. algoa feeds on spring blossoms of Nama hispidum and Eriastrum.
More information on the entire family Meloidae, the Blister Beetle family, can be found on the info page on BugGuide which indicates:  “Life cycle is hypermetamorphic. Larvae are parasitoids. Hosts include bees of families Megachilidae and Andrenidae. Epicauta (and other genera) larvae prey on eggs of grasshoppers.

Eggs are laid in batches in soil near nests of hosts, sometimes in nest of bee host, or on stems, foliage, or flowers. Larvae undergo hypermetamorphosis–first instar larvae (usually called triungulins) are active, have well-developed legs and antennae. These typically search for hosts. Later instars tend to have reduced legs and be less active, having found hosts. There is a coarctate (pseudopupal) stage, which is usually how the larvae overwinter. Life cycle may be as short as 30 days, or as long as three years.

It is typically one year, corresponding to that of host.”  Other remarks include:  “Pressing, rubbing, or squashing adult blister beetles may cause them to exude their hemolymph (“blood”), which contains cantharidin. This compound causes blistering of the skin, thus the name blister beetle. Accidental or intentional ingestion of these insects can be fatal.

There are documented incidents of horses dying after eating hay in which blister beetles were inadvertently baled with the forage. Watch that curious children do not attempt to put these beetles in their mouths. The external use of cantharidin, commercially known as “Spanish fly,” the supposed aphrodisiac, is likewise discouraged.

Letter 14 – Iron Cross Blister Beetle

Prettiest beetle I’ve ever seen?
April 27, 2010
I’m in Phoenix, AZ and found this beautiful creature while on a walk around my work in a business park. I followed this insect around for a couple of minutes trying to get pictures, but he was pretty fast. Something tells me this is not a beetle, but I just don’t know. Usually I am completely freaked out by bugs of any sort, but this one had me interested. I’ve showed several friends and they are also “eh” on this one. Any ideas?
whatevah is clevah
Phoenix, AZ

Iron Cross Blister Beetle

to whatevah,
This is an Iron Cross Blister Beetle.  We provided a very lengthy answer for the letter and photo also from Phoenix that we posted just yesterday and you may read it here.

Letter 15 – Iron Cross Blister Beetle

Our house is infested (atleast 200)with this Black/red/yellow beetle type bug, Please tell us what it is!
May 2, 2010
Our house is infested (atleast 200)with this Black/red/yellow beetle type bug, Please tell us what it is!
• Your letter to the bugman    As of today, we went outside and found about 200 of these bugs in one small area in our yard. The have a beetle type body that is yellow with a black cross on them and a bright red head. They move very fast and dont die easily.

I live in Phoenix and we have never seen them before. They are about 1 inch long, but some a little bigger or smaller. We have a baby almost here and I want to make sure they are not poisonous. I appreciate your help!
Thank for your help! Nicole
Phoenix Arizona

Iron Cross Blister Beetle

Hi Nicole,
Your letter is at least the third we have gotten in the past week requesting an identification for an Iron Cross Blister Beetle, though you letter is the only one that has indicated a high population density.

Letter 16 – Drawing of Iron Cross Blister Beetle

Beetle like bug with bright yellow on the top of the body, black underneath, and a small read head.
May 2, 2010
I saw this bug walking down my driveway and was really amazed by it! I have lived in Phoenix, Arizona for 57 years and have never seen anything like it! It was between 3/4″ and 1″ in length. It had bright yellow on the top, maybe wings, maybe not.

There was a black line down the center and black lines slanting from about two thirds down the body outward and down like a peace sign on it’s back. These lines were noticeable but not thick. Mostly, all I could see was this bright yellow bug with a small red head.

There wasn’t a segment between the main body and the head, just the body and the head. The head was squarish and really, really red! I have attached a rather crude drawing. I hope it rings a bell for someone.
Sun City, Arizona

Iron Cross Blister Beetle

Hi Kerry,
There is little doubt in our mind that you saw an Iron Cross Blister Beetle, probably Tegrodera algoa which is featured on BugGuide.  This is the fourth letter requesting an identification from Phoenix this week, so the beetles might be especially plentiful this year due to the rains. 

We are setting your letter to post on Mother’s Day as we are taking a holiday to visit Mom in Ohio and we do not want to deprive our loyal readership of a daily update on the insect world.

I don’t think this is the same bug. There wasn’t a ridge down the center of the back, the black lines on the back were not as prominent and not like a cross but like a peace sign. There was no segment between the body and the head and the head was square. Like I said, I have never seen a bug like this. I sure wish I had been able to catch it and get a photo. Might it be a mutant cousin?
Kerry Dennis

We stand by our original identification.  Since there is no photograph, we cannot confirm nor deny.

Ed. Note: Often identifications based on photographs are difficult, but identifications based on crude drawings are nearly impossible.  Let us know if you think we made the right call.

Iron Cross Blister Beetle

Letter 17 – Iron Cross Blister Beetle

May 3, 2010
Just showed up – May 2010 – desert garden – phoenix, AZ
Phoenix, AZ USA

Iron Cross Blister Beetle

Hi Leisel,
This is an Iron Cross Blister Beetle, and your letter is the fourth confirmed identification we have posted in the last week, all from the Phoenix area. 

A fifth letter contained a very crude drawing that may have been done by a three year old, and when we identified it as an Iron Cross Blister Beetle, the Doubting Thomas that submitted the identification request rejected our identification.

Another Iron Cross Blister Beetle sighting, without a photo
Iron Cross Blister Beetle
May 4, 2010
I have tons of these things in my yard. I do not have a personal picture but copied one from another page and know what they are by the other posts I have seen on them. Just would like to know if they are a danger to mine or my dog’s health, and if there is a way to turn their direction away from my house.
D. Ellison
Tucson, AZ

Dear D.
We do not know how to keep the Iron Cross Blister Beetles away from your home.  Do not try to handle them or you might have a skin reaction.  We do not recommend allowing your dog to eat them.  We have heard of incidents where horses eating Blister Beetles with hay have gotten ill.

Letter 18 – Iron Cross Blister Beetle

One inch long, red head, yellow wings, black body
May 6, 2010
My wife saw two lizards fighting over food and upon further inspection she discovered this tasty morsel (to lizards anyway). My 3-year-old daughter loves this bug and named it Basta.
Mr. Moffitt
Tucson, AZ

Iron Cross Blister Beetle

Dear Mr. Moffit,
This is an Iron Cross Blister Beetle.

Letter 19 – Iron Cross Blister Beetle

Mystery Red Bug in Tucson, AZ
May 17, 2010
Hello Bugman,
I was working in my backyard garden this afternoon when I spotted something red and yellow moving about in a small flower bush. I was shocked by it because I could not quickly place it into any generic category.

I could not call it an ant or beetle or bee and my husband and I have been baffled ever since. It peacefully ate flower buds while we photographed it. My husband commented that it had “personality” in the way it grasped at leaves and maneuvered through the bush to find and eat buds.

I have never seen anything like this and I hope somebody can identify it for us. I wonder too, should I expect to see any more of these in my back yard this summer?
South-East Tucson, Arizona

Iron Cross Blister Beetle

Hi Diana,
We have gotten more reports of Iron Cross Blister Beetles from Arizona this year than in any other year since we began this online column ten years ago.  Expect to see them until through June.

Letter 20 – Iron Cross Blister Beetle

What is this thing?
Location: Bishop, California
December 11, 2010 8:06 pm
I saw a group of these on a small weed just south of Bishop California in eastern California on Route 395. I haven’t been able to identify it through any books or online resources that I’ve found.
Signature: Donald

Iron Cross Blister Beetle

Dear Donald,
This unusual beetle is an Iron Cross Blister Beetle in the genus
Tegrodera.  Many years ago when we received our first image of one of these incredibly colored beetles, we were awe struck by its beauty. 

That initial impression has never faded.  Blister Beetles should be handled with care as they exude a compound known as cantharidin that causes blistering of the skin.  Blister Beetles have very complex life cycles and you can read about them in our archive and on BugGuide.

Iron Cross Blister Beetle

Letter 21 – Iron Cross Blister Beetle

Subject: Appears to be a Beatle like
Location: Phoenix Arizona
May 8, 2013 9:09 pm
Found this in the back yard over and inch close to two inch. Yesterday so season is late spring. Location is Gilbert Arizona. So just outside of Phoenix.
Signature: SMC

Iron Cross Blister Beetle
Iron Cross Blister Beetle

Dear SMC,
This is our first Iron Cross Blister Beetle sighting this spring.  Each spring we get several identification requests from Arizona for this distinctively colored and marked beetle.

Letter 22 – Iron Cross Blister Beetle

Subject: Unknown Beetle ?
Location: Arizona, United States
April 17, 2014 12:39 pm
This beetle like insect appeared yesterday on my block wall, I went to the other side of the wall and they were in 100’s in a vacant lot with scrub desert brush climbing the wall. Temps were 95ish. They are at least an inch long and very colorful. What is it and is it an issue in my garden?
Signature: Pat Z.

Iron Cross Blister Beetle
Iron Cross Blister Beetle

Hi Pat Z.,
This Iron Cross Blister Beetle in the genus
 Tegrodera is one of the most distinctive looking North American Beetles.  The bright colors of the Iron Cross Blister Beetles are aposomatic, and provide a warning that the beetles are capable of releasing a blistering agent known as cantharadin from their joints, so they should be handled with caution.

Thank you so much, I could not find it anywhere with a picture

Letter 23 – Bug of the Month May 2014: Iron Cross Blister Beetles

Subject: Identifying an insect
Location: Saguaro National Park East in Tucson, Arizona
May 1, 2014 4:41 pm
While hiking in the Saguaro National Park East today, we encountered bugs that we had not seen before. They had red heads or eyes, with spotted yellow/green on their backs. The bug, itself was black underneath.

They crawled at a good pace but seemed to like clinging to the small plants with leaves, possibly eating the leaves. They were about an inch in length. Today is May 1, 2014 and like I said, we had never seen them before and we hike there at least 4 times a week.
Signature: R A Kirby

Iron Cross Blister Beetles
Iron Cross Blister Beetles

Dear R A Kirby,
These are Iron Cross Blister Beetles in the genus
Tegrodera, and we generally get a few identification requests from Arizona and occasionally California each spring.  We are making this our Bug of the Month for May 2014.  The bright coloration is quite distinctive as well as being aposomatic or warning coloration. 

Blister Beetles in the family Meloidae are able to secrete a compound, known as cantharadin, that might cause blistering in human skin.  The aphrodesiac Spanish Fly is made by grinding the bodies of a European Blister Beetle.  According to the Sonoran Desert Naturalist

“Normally these beetles emerge in large numbers in mid to late spring and move together in bands crawling or running across the ground. They feed on succulent leaves and flower petals. The larva stage is subterranean and likely is parasitic in nests of ground-nesting bees.” 

Letter 24 – Iron Cross Blister Beetle

Subject: who is this?
Location: Tucson Arizona, Sonoran Dessert.
May 5, 2014 12:00 pm
Hello Bug man,
My name is Brodrik, and I live in the desert west of Tucson Arizona. Many of these flying insects have made their presents know here recently, and I wonder how they are called in the science world so that I may investigate why they are now here and visable.
Many thanks,
Signature: Bug man

Iron Cross Blister Beetle
Iron Cross Blister Beetle

Dear Brodrik,
This is an Iron Cross Blister Beetle in the genus
Tegrodera, and each spring, they make seasonal appearances in desert areas of Arizona, California and Baja.  It is our Bug of the Month for May 2014.

Letter 25 – Iron Cross Blister Beetle

Subject: Bug in garden
Location: Southern California
April 21, 2015 3:58 pm
Found this in my garden in carlsbad, ca around 2pm on 4/21/2015. What is it?
Signature: Carole

Iron Cross Blister Beetle
Iron Cross Blister Beetle

Dear Carole,
This distinctive beetle is an Iron Cross Blister Beetle.

Letter 26 – Iron Cross Blister Beetle

Subject: So Cal Beetle?
Location: Sage, California (15 miles East of Temecula, CA)
July 24, 2015 4:16 pm
We’ve found this beetle in Sage California in a sage chaparral area. It is a beetle shaped like a stink beetle and is approximately 1 to 1 1/2″ long.
They are found in groups of 1-7 on buckwheat plants.

They may have dug out of the ground and left behind a small mound of dirt (like worm castings) in a small target pattern.
We haven’t seen them for about 10 years: it last snowed here about ten years ago, and then this last winter.
Signature: Thanks, Daren

Iron Cross Blister Beetle
Iron Cross Blister Beetle

Dear Daren,
This Iron Cross Blister Beetle in the genus
 Tegrodera probably has seasonal spikes in population when conditions are best to support larger populations, but we do receive at least a few requests from the Southwest each spring to early summer.  This is a later sighting than usual.

Letter 27 – Iron Cross Blister Beetle

Subject: Manzanar bug
Location: Manzanar, CA
May 31, 2016 10:54 am
Can you please let me know what this is?
Signature: Jen

Iron Cross Blister Beetle
Iron Cross Blister Beetle

Dear Jen,
This is one of our favorite last spring sightings from California and Arizona, the Iron Cross Blister Beetle.  Blister Beetles in the family Meloidae should be handled with caution as they are able to exude a compound known as cantharidin that may cause blistering in human skin.

Letter 28 – What Ate the Iron Cross Blister Beetle???

Subject: unidentified insect
Location: Phoenix, AZ
April 14, 2017 3:36 pm
Hi Bugman,
I was in Phoenix, AZ last week (first week of April) and found what was left of an insect in the grass. I think a bird ate the abdomen of this insect? Maybe the wing spread was 2″? I tried to identify it by looking at pictures on line, but I have struck out thus far. Can you help me identify this interesting looking insect?
Thank you,
Signature: Dawna

What Ate the Iron Cross Blister Beetle???

Dear Dawna,
We always love receiving and featuring our first Iron Cross Blister Beetle from the genus
Tegrodera each spring, and this year that distinction goes to your submission, however we generally are thrilled to receive a living example.  We are quite curious what ate the fatty abdomen on your individual and left behind the harder elytra, legs and front of the body. 

We often receive images of Prionids and Cicadas that have been eaten in a similar manner, and we suspect birds are the predators in question.  The curious thing about your Blister Beetle is that it is a member of a family that is known for the ability to secrete the compound cantharidin that causes blistering in human skin and that could make horses quite ill if they ingest Blister Beetles while eating hay.

Letter 29 – Iron Cross Blister Beetle

Subject: Yellow black spots red head
Location: Phoenix Arizona
April 15, 2017 10:20 pm
I found this in the parking lot in Phoenix Arizona in April 2017. I moved it to the flower bed.
Signature: Alan

Iron Cross Blister Beetle

Dear Alan,
We actually identified your Iron Cross Blister Beetle from just your subject line, though it did help that it was fresh on our mind since just yesterday we posted the first image of an Iron Cross Blister Beetle of the season, also from Phoenix, that had been preyed upon by an unknown predator.

Letter 30 – Iron Cross Blister Beetle

Subject: Tegrodera aloga
Location: Chandler, AZ
May 29, 2017 6:53 pm
In my backyard, Chandler, AZ – awesome looking!
Signature: JD

Iron Cross Blister Beetle

Dear JD,
The Blister Beetle family Meloidae includes many brightly colored and unusually patterned members, but the Iron Cross Blister Beetles in the genus
Tegrodera are probably the most remarkable looking.  The coloration is surely aposomatic or warning coloration due to the beetle’s ability to secrete the compound cantharidin that is a known blistering agent to human skin.

Letter 31 – Iron Cross Blister Beetle

Subject:  Beetle, red, yellow, black
Geographic location of the bug:  Phoenix, AZ
Date: 04/30/2019
Time: 05:23 PM EDT
Your letter to the bugman:  Saw this in our back rose bed. Could not find anything like it online.
How you want your letter signed:  Puzzled in Phx

Iron Cross Blister Beetle

Dear Puzzled in Phx,
The first time we ever received an image of gaudily colored Iron Cross Blister Beetle, we thought we were looking at a toy bug.  They would seem to be right on time based on our posting five identification requests of Iron Cross Blister Beetles at the beginning of May 2010.  Populations of individuals will vary from year to year.


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17 Comments. Leave new

  • Thanks for having some info on this was not sure what this was and weather it would hurt my dog. I live in AZ and they are running around in the dirt. I will take caution..

  • Christopher Franklin
    April 30, 2014 10:19 am

    I have come across several of these Iron Cross beetles in Northern Apache Junction AZ this year

    • We generally get several identification requests for Iron Cross Blister Beetles from Arizona each spring.

  • For the past three days I saw this weird insect named Iron Cross Blister Beetles in my backyard, first were only two, but in the last day there were four of them; and I have a question, What would happen if this insect was in contact with my dog, he had started to scratch itself, he didn’t do it before; It can be a problem? May this insects caused something? What should I do?.
    I’m from Sonora, but is the first time I see this kind of insect. Thank You 🙂

  • For the past three days I saw this weird insect named Iron Cross Blister Beetles in my backyard, first were only two, but in the last day there were four of them; and I have a question, What would happen if this insect was in contact with my dog, he had started to scratch itself, he didn’t do it before; It can be a problem? May this insects caused something? What should I do?.
    I’m from Sonora, but is the first time I see this kind of insect. Thank You 🙂

  • Joshua Vasquez
    April 17, 2015 5:16 pm

    Me and my son found an cross blister beetle under our back stairs outside. I wish I could post a picture. For you but we let it go because my son can’t keep his hands off anything and im not having or letting him get any blisters on his hands or face

  • We have lived in Marana, az for 14 years…..we got these beetles this year…. Why? We have never seen them before…and we are outdoors a lot around our yard…What’s up this year….Thanks, Darcy

    • Insect populations fluctuate from year to year based on food supplies, weather conditions and other factors. We don’t know what is causing your local situation, but we have not received an unusually high number of reports of Iron Cross Blister Beetles this year.

  • a few days ago while outside, i noticed some stinging and thought a bug was biting me, i looked down and there was white liquid on my arm, i wiped it away and later a blister formed. a couple days later i found this brightly colored insect and looked it up to find that it is an iron cross blister beetle! now the mystery of my blister is solved!

  • Robert Maccagno
    May 14, 2015 4:03 pm

    Is it common for the Iron cross beetle to attack!
    I was spraying them with bug spray as I must have had some 2-3 hundred in my backyard and was attacked toward my head by 2 of them!
    It was like they were on a mission.
    Been at this property 3 yrs, first time I’ve ever seen them!
    Nowhere can I find that they fly!
    Thanks for the info.
    Queen Creek ,AZ

    • The beetles are getting sprayed with bug spray and you suspect they are attacking???
      We do not believe they were on a mission. It is more likely that the spraying agitated them and they took to the air, possibly disoriented by the poison. We would encourage you to accept their presence and learn to coexist.

  • Reply
  • We are seeing these Iron Cross Blister Beetles in Far North Scottsdale right now. 5/2020

  • “T. algoa”. Should be T. aloga. 3rd line.


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