Blister Beetle: Quick Guide to Identify and Manage Infestations

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Blister beetles are fascinating insects belonging to the family Meloidae.

They exhibit a wide range of colors, sizes, and body shapes, with their most distinctive feature being a narrow thorax and wider head, differentiating them from most beetles.

These beetles are commonly known for the cantharidin toxin present in their body fluids, which can cause blisters on human skin upon contact and life-threatening inflammations in horses and livestock.

Blister Beetle

The lifecycle of a blister beetle is quite intriguing. Blister beetle larvae primarily feed on clusters of eggs, and they overwinter in the soil before emerging as adults in late spring or early summer.

While they are commonly found infesting alfalfa, they may also feed on numerous other host plants such as pigweed, goldenrod, goathead, puncturevine, peanuts, soybeans, and more.

Knowing these characteristics can help raise awareness of blister beetles and their potential impact on humans, horses, and livestock. Stay cautious around these insects, as their toxin can pose serious health risks.

Identification and Characteristics

Appearance and Size

Blister beetles belong to the insect family Meloidae and have a distinct body shape with a narrow thorax and a wider head.

Most of these beetles showcase an elongate, cylindrical abdomen. They vary in size from 3/8 to 1 inch long.

Color and Patterns

  • Some blister beetles have solid colors, like gray or black.
  • Others have paler wing margins, metallic shades, or yellowish stripes/spots.

Antennae and Stinger

Blister beetles have antennae, but they do not possess a stinger. Instead, they secrete a toxic defensive chemical called cantharidin, which helps protect them from predators.

Striped Blister Beetle

The Striped Blister Beetle (Epicauta vittata) is a common species found primarily in the United States. It has distinctive black and yellow stripes on its body.

Margined Blister Beetle

Another common type is the Margined Blister Beetle, which features:

  • Gray or black body
  • Paler wing margins for contrast

Desert Blister Beetle

The Desert Blister Beetle (Meloe rugosus) is commonly found in arid regions of the southwestern United States.

Characterized by its dark, metallic blue or black hue, this beetle thrives in desert environments.

Like other blister beetles, it contains the toxin cantharidin, which can cause skin blisters upon contact.

Green Blister Beetle

The Green Blister Beetle (Lytta polita) sports a vibrant green exoskeleton.

Found primarily in North America, this beetle is attracted to flowering plants.

Its bright coloration serves as a warning to predators about the toxic cantharidin it carries.

Iron Cross Blister Beetle

The Iron Cross Blister Beetle (Tegrodera aloga) is easily recognizable by the bright orange or red cross on its back.

Predominantly found in the southwestern U.S., it is most active during the summer months.

As with other blister beetles, it produces cantharidin as a defense mechanism.

Red Headed Blister Beetle

The Red Headed Blister Beetle (Meloe angusticollis) features a contrasting color scheme with a red head and black body.

Commonly found in the eastern U.S., it frequents gardens and meadows. Handling this beetle can lead to skin irritation due to its cantharidin content.

Blister Beetle Life Cycle

Eggs and Larval Stage

Blister beetles spend the winter in the larval stage1.

After hatching from eggs2, the mobile triungulin larvae3 actively search for their hosts, usually bee or grasshopper eggs4.

Upon finding them, they begin feeding.

Some interesting facts about the Blister Beetle Larval Stage are:

  • The eggs hatch as tiny, mobile triungulin larvae3
  • The larva reaches its feeding site on its own or attaches to an adult bee and is carried there1

Female and Males

During early summer, adult blister beetles emerge from their pupal stage2.

Females and males have distinct roles within the life cycle: adult females lay clusters of eggs in the soil3, while males primarily focus on mating.

Mating and Reproduction

Mating is an essential part of the blister beetle life cycle2. After finding each other, males and females mate to produce offspring, and the females proceed to lay clusters of eggs in the soil3.

Comparison Table of Blister Beetle Life Stages:

Life Stage Duration Activity
Larval Winter1 Feeding on host eggs4
Pupal 2 weeks in the spring2 Developing into adults2
Adult Female Early summer2 Laying eggs in soil3
Adult Male Early summer2 Mating with females2

Habitat and Distribution

United States and Florida

Blister beetles inhabit various places across the United States, including Florida. They can be found on:

  • Plants: Feeding on leaves
  • Flowers: Larvae often found in flowers or attached to them

Grassy Fields and Alfalfa Fields

These beetles can be commonly found in alfalfa fields, as well as grassy fields and areas near rangeland pastures. They tend to feed on:

  • Alfalfa hay: High numbers in hay pose a danger to livestock
  • Amaranthaceae, Asteraceae, Solanaceae plants: Blister beetles feed on these plant families

Comparison of Habitats:

Habitat Examples Plant Families
United States Florida Various
Grassy & Alfalfa Fields Amaranthaceae, Asteraceae, Solanaceae

Feeding and Interactions with Plants

Plant-Feeding Insects

Blister beetles are plant-feeding insects that consume various plant parts, like flowers, leaves, and fruits.

They usually feed on nectar and pollen and can damage petals, other floral parts, and even defecate within flowers.

Damage to Crops and Leaves

Blister beetles, in addition to affecting flowers, can also cause significant damage to crops and leaves.

The cantharidin toxin found in their body fluids can lead to life-threatening inflammations in horses and livestock, especially when they accidentally consume these beetles along with their fodder.

Some examples of crops that these beetles often attack include:

  • Alfalfa
  • Clover
  • Soybeans

Below is a comparison table of the main characteristics of blister beetles:

Characteristics Blister Beetles
Color Varies (black, grey, or brightly colored)
Size 3/4 to 2 cm body length
Feeding Nectar, pollen, and plant tissues
Damage Flowers, leaves, and crops

Effects on Animals and Humans

Cantharidin and Its Chemical Properties

Cantharidin is a toxic chemical found in blister beetles that affects both animals and humans.

This compound is used by male beetles as a defense mechanism and given to females during mating, which in turn protects their eggs from predators1.

Blister Beetle Dermatitis and Skin Reactions

Humans exposed to cantharidin may experience skin reactions, including:

  • Painful blisters
  • Welts or warts
  • Redness and swelling

It is essential to be cautious when handling blister beetles to avoid contact with cantharidin and these skin reactions2.

Poisoning in Horses and Precautions

Blister beetles pose a significant threat to horses, as consuming even 25 to 300 beetles could be lethal3. Some precautions horse owners can take include:

  • Inspecting hay for blister beetles before feeding
  • Avoiding hay from fields adjacent to rangeland pastures, which have a higher risk of beetle infestation4
  • Consulting a veterinarian immediately if blister beetle poisoning is suspected

Comparing the effects of cantharidin in humans and horses:

Effects on Humans Effects on Horses
Skin blisters Lethal poisoning
Welts or warts
Redness and swelling

By understanding the dangerous properties of cantharidin in blister beetles, we can take necessary precautions to protect both human health and animal well-being.

Control and Management

Preventing Infestation in Agricultural Fields

Preventing infestation of blister beetles in agricultural fields can save crops from damage and protect livestock from potential harm. It’s essential to:

  • Monitor fields regularly: Inspect your crops during the growing season to identify any presence of blister beetles early on.
  • Manage field borders: Make sure to control weeds and maintain clean border areas to reduce blister beetle habitat.

Hay fields adjacent to rangeland pastures are at higher risk for blister beetles.

Handling and Personal Protection

When dealing with blister beetles, appropriate protective measures are crucial to prevent painful blisters. Some essential precautions include:

  • Wear long-sleeved shirts, pants, and gloves: Covering your skin can prevent contact with their toxins.
  • Use soapy water: If you encounter a blister beetle, use soapy water to gently remove it and prevent injury.

If toxins get in your eyes, seek immediate medical treatment.

Professional Assistance

When blister beetles are in high numbers or if you are uncertain about managing their control, professional assistance can be valuable. Reach out to:

  • Veterinarian: Ensure proper treatment for affected animals, especially regarding ingestion of baled hay containing blister beetles.
  • County agent: They can help identify infestations and provide guidance on management strategies.
  • Entomologist: An expert in insect identification and management can provide recommendations tailored to your specific needs.

Interesting Facts and Historical Uses

Spanish Fly and Aphrodisiac Uses

Blister beetles are known for their secretions containing a substance called cantharidin, which has historically been used in the production of Spanish Fly.

Spanish Fly is an infamous aphrodisiac that has been used for centuries.

Interestingly, it works by causing irritation and a burning sensation in the areas it comes in contact with, stimulating blood flow and creating a sensation of sexual arousal.

However, its use is risky, as too much of the substance can lead to dangerous side effects, such as:

  • Swelling
  • Scarring
  • Poisoning

Antibiotic Properties

Apart from its aphrodisiac applications, cantharidin has potential antibiotic properties. Some studies have shown that the substance can be effective against certain bacteria, such as:

  • Staphylococcus aureus
  • Escherichia coli

Note: Further research is needed to confirm the antibacterial potential of cantharidin from blister beetles.

Spanish Fly (Aphrodisiac) Antibiotic Properties
Effects Irritation, burning Potential antibacterial activity
Risks Swelling, scarring, poisoning Further research needed
Historical/Modern Use Centuries-old aphrodisiac Experimental

In conclusion, the blister beetle and its secretion, cantharidin, have had a long and intriguing history of use.

From their notorious aphrodisiac effects in Spanish Fly to their possible antibiotic properties, these insects continue to be a subject of fascination and study.


Blister beetles, with their distinctive appearance and intriguing lifecycle, play a unique role in the insect world.

Their secretion, cantharidin, has both historical and potential modern applications, from the notorious aphrodisiac Spanish Fly to potential antibiotic properties.

However, their toxic nature poses risks to humans, livestock, and crops.

Awareness and understanding of these beetles are essential for safe interactions and effective management in agricultural settings.


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Reader Emails

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

Letter 1 – Master Blister Beetle

Flying desert insect, resembles ant
Location: Mojave Desert, near the mountains
April 22, 2011 10:43 pm
A friend and I found swarms of this red ant-like insect with wings near a mountain range in the Mojave Desert, during spring. The bugs are about 1 to 1.5 inches long, and they were non-hostile. We have no idea what kind it is, but we would like to know.
As a side note, most of them were mating.
Signature: Aethryix

Master Blister Beetle

Dear Aethryix,
The appearance of large numbers of Master Blister Beetles,
Lytta magister, is a common occurrence in the Mojave and Colorado Deserts of the arid southwest each spring, and we hope you enjoyed the sighting.  Like other members of the Blister Beetle family, the Master Blister Beetle should be handled with care, or even better, not handled at all, because they are able to secrete a compound known as cantharidin that can cause blistering of the skin. 

Though Blister Beetles are found in many parts of the world and throughout much of North America, the deserts of the arid southwest have an especially diverse population and there are many unusual looking species.  We are sad you did not submit any images of mating Master Blister Beetles, though there is no shortage of such images in our archives including this example from earlier this year. 

Adult Master Blister Beetles feed on vegetation and we would expect the rain pattern from this past winter would have provided for a lush plant growth in the desert which should in turn support a robust population of insects that feed on vegetation, including Blister Beetles.  We needed to check the extent of the Colorado Desert online to provide a state for this posting, and we learned on the California Fish and Game website that the Colorado Desert is entirely in California while the Mojave Desert extends to some neighboring states.

Letter 2 – Nuttall’s Blister Beetle from Canada

Shiny, black beetle
Location: southern Saskatchewan
June 28, 2011 9:32 pm
We live in southern Saskatchewan, Canada. We live in a very rural area of the province and grow lots of grain.
Found it in late June.
Signature: Thanks!

Nuttall’s Blister Beetle

You should exercise caution when handling Nuttall’s Blister Beetle, Lytta nuttalli, as well as other members of the family Meloidae.  Blister Beetles can secrete a substance called cantharidin that can cause skin to blister.

Letter 3 – Master Blister Beetle

Subject:  What is this thing!?
Geographic location of the bug:  29 Palms, CA
Date: 04/08/2019
Time: 10:03 PM EDT
Your letter to the bugman:  Saw several of these critters crossing the dirt path as I was walking my dog. Took a couple shots and had on on the tip of my walking stick, hunched up with it’s butt angled down like it was stinging, and the front legs up looking poised for combat.

Couldn’t get a shot of it like that since i was holding the stick and dog and camera and didn’t want to let the dog go in case they were stinging bugs…I at first thought they were velvet ants but nope…can’t find anything that looks like it online. they were about 1.5 to 2 inches in length…when i stopped to take pictures they all altered their path and came at me…what are they??
How you want your letter signed:  thanks, John Roush

Master Blister Beetle

Dear Josh,
This is a Master Blister Beetle, and though it does not sting, it does possess aposomatic or warning colors along with many Blister Beetles in the family Meloidae.  According to BugGuide:  “Pressing, rubbing, or squashing blister beetles may cause them to exude hemolymph which contains the blistering compound cantharidin.

Ingestion of blister beetles can be fatal. Eating blister beetles with hay may kill livestock. Cantharidin is commercially known as Spanish Fly.”  We get several images of Master Blister Beetles from southern California and Arizona each April.  Just last week Daniel went to Joshua Tree National Park and he hoped to encounter some Blister Beetles, but alas, he returned without a single sighting.

Master Blister Beetle

Letter 4 – Master Blister Beetle

Can anyone identify these guys for me
Location: LaQuinta California (Mojave Desert)
June 21, 2011 3:43 am
I’m new here. Can anyone identify these guys?
Signature: unsigned

Master Blister Beetle

Hi unsigned,
This is a Master Blister Beetle,
Lytta magister, and there is much information on the species in our archive.

Letter 5 – Large Eared Blister Beetle: Cissites auriculata

Location: Brownsville, Texas
January 10, 2011 11:38 am
This beetles is approximately 1.25 inches long. Reddish brown with black spots, legs and pinchers. Sorry they’re a bit blurry.
Signature: Pam Neuburg

Large Eared Blister Beetle: Cissites auriculata

Hi Pam,
This positively spectacular looking beetle is a Blister Beetle,
Cissites auriculata, the Large Eared Blister BeetleAccording to BugGuide, the range is “West and South Texas, Mexico south to Costa Rica. Bahamas & Puerto Rico.” 

There is a posting on BugGuide with a very robust comment section, including:  “This probably is only the 2nd record from Texas (& the USA). Lewis recorded the species from the Chisos Mts. in 2004 (Coleop. Bull. 58: 635). The genus is known to parasitize Xylocopa”  which are Carpenter Bees.

Thank you so very much! Love your site.
Pam Neuburg

Letter 6 – Master Blister Beetle

Anza Borrego Bug
March 23, 2010
I came across this bug while hiking in the Anza Borrego State Park, near the Salton Sea, in Southern California in the afternoon of March 13th, 2010.It was about 100 yards from a blooming Ocotillo plant. I found it quite beautiful and would like it identified. Your help would be much appreciated.
Ashley Bacon
Anza Borrego State Park, Southern California

Master Blister Beetle

Hi Ashley,
Each spring, we get reports of sightings of Lytta magister, the Master Blister Beetle, from the Mojave and Colorado deserts in California and Arizona.  Though BugGuide reports them from Nevada and Utah as well, we have not received any reports from those states. 

Your photo is the first one this year.  Blister Beetles are a diverse family with numerous species living in the desert areas of the Southwest.  Generally the adults are seen each year for a short period of time, usually in the spring when they feed on new plant growth.  The larvae are parasitic on grasshopper eggs or the eggs of solitary bees.

Letter 7 – Master Blister Beetle

Subject: red-headed bug???
Location: Tahquitz Canyon, Near Palm Springs, CA
March 7, 2015 2:33 pm
I was hiking in Tahquitz Canyon near Palm Springs, CA yesterday and spotted this bug crawling across the path. It’s almost 2″ long.
Can you let us know what it was?
Many thanks,
Signature: Stu

Master Blister Beetle
Master Blister Beetle

Dear Stu,
This distinctive beetle is a Master Blister Beetle, and your image is the first of what we suspect will be numerous others that are sent to us this spring.

Letter 8 – Big Eared Blister Beetle from Mexico

Subject: What is this?
Location: Guadalajara, Mexico
February 9, 2013 1:02 pm
This landed on a chair in my garden (I live in Guadalajara, Mexico). Very pretty – did not seem too bothered by a camera being close. Big black pincers at the front. Did not appear aggressive.
Signature: Phil

Big Eared Blister Beetle

Hi Phil,
This is a Big Eared Blister Beetle,
Cissites auriculata, or another species in the genus.  According to BugGuide, its range is:  ” W. and S. TX / Mexico south to Costa Rica / Bahamas & Puerto Rico.  Only recently recorded from the US. (Lewis 2004).”  BugGuide also indicates it:  “Parasitizes carpenter bees, Xylocopa spp.”  

Letter 9 – Big Eared Blister Beetle from Nicaragua: Cissites auriculata

Subject: BIG crazy beetle Nicaragua
Location: Playa Guasacate, Nicaragua
May 3, 2015 1:20 pm
Hello Mr. Bugman,
I am very curious what this large beetle might be. I looked all over online but did not find anything.
It was approx. 2 inches long, very orange big pincers on front and had large black spots. It almost looked fake! Cool and scary looking little guy. Would you be able to identify him for me?
Oh yes and I found it in the Southwest beach town called Playa Guasacate, Nicaragua.
Signature: Bug mystery solved

Blister Beetle:  Cissites auriculata
Blister Beetle: Cissites auriculata

The first time we received an image of this unusual Big Eared Blister Beetle, Cissites auriculata, we didn’t even recognize it as a member of the family.  According to BugGuide, it is found:  “w. & so. TX to Costa Rica; W. Indies” and “only recently (2004) found in the US” perhaps as a symptom of global warming.

Letter 10 – Margined Blister Beetle

OMG, I think he’s ANGRY! Canonsburg, PA
PLEASE, for the love of GOD, WHAT have I ticked off here?? I’ve searched your pages, and the closest I’ve come is the marginal blister beetle. Whatever he is, he’s mad, and until I can identify him, I’m not venturing back outside!
Misty Doy

Hi Misty,
We concur with your identification of a Margined Blister Beetle, Epicauta funebris. We hope you have a good book to entertain you until it is safe to venture back out into the yard, or you could just plod through our archive which should take several months.

Letter 11 – Margined Blister Beetle

bug identification
I sent a picture of these bugs the other day-then I read your message about location! I am in Blue Mound, IL which is in the heartland of the Midwest. THese bugs are devouring my green bean leafs and beans. In these photos, they are feeding! I would like to know what they are-are they any benefit to anything at all? Thanks,

Hi Marla,
This is a Margined Blister Beetle, Epicauta funebris. Since we are artists and not entomologists, we are permitted to have whacky theories about insects without worrying about seeming ridiculous to our peers. Many Blister Beetles are found in areas of arid climate. We have pondered the unusual life cycle of Blister Beetles for some time now.

When the adult Blister Beetles appear, it is often in great numbers, and their ravenous appetites cause them to defoliate plants. The immature Blister Beetles do not compete with adults for food as the larvae of many genera feed on the eggs of grasshoppers.

Grasshoppers would compete with the adult Blister Beetles for food in areas where food is scarce, so the larvae are helping to reduce the population of insects that compete for food with the adults. Thank you for writing back with your location.

Letter 12 – Margined Blister Beetle

Insect Identification
This bug, and it’s many friends and relatives, has been decimating my tomato plants. I do not seem to be able to find any mention of or identification for it anywhere. Can you help me? I live in Flat Rock, Alabama, which is in the north eastern corner of the state, at about 1300 to 1400 feet elevation, on a plateau above the Tennessee River called Sand Mountain. Thank you so much.
Sherry Johnson

Hi Sherry,
This is a Margined Blister Beetle, Epicauta pestifera. It usually infests soybeans. You can find more information on this BugGuide page.

Letter 13 – Margined Blister Beetle

Help with bug / beetle ID?
I’ve never noticed any bug like this before but this one was on the cement block of my home just behind the rose bushes on July 30th of this year. I live in north central Ohio. Any ideas of what it may be? Sorry the pictures aren’t so clear, I’m having difficulty with that lately. Thanks for any info.
Jill Johns
Ashland, OH

Hi Jill,
This is a Margined Blister Beetle.

Letter 14 – Margined Blister Beetles

bug with a big appetite
This beetle can eat a lot of plant quickly. What is it? Thanks,

Hi Steve,
These are Margined Blister Beetles.

Letter 15 – Margined Blister Beetle

What is this bug.
Found him on a butterfly bush in my Mother’s garden. Thought he was a type of Tiger Beetle, but I haven’t found any with this markings in any of the galleries I’ve looked through.

Hi Kammie,
This is a Margined Blister Beetle, Epicauta pestifera, not a Tiger Beetle.

Letter 16 – Margined Blister Beetle

bugs on my tomato plants
Hi. I read the whole section on tomato bugs, but I cannot seem to figure out what is going on with my tomato plants. I saw a large hornworm on the plant a few weeks ago, but not knowing what it was, I didn’t do anything about it.

I was away for a few days and I came home to find one of my plum tomato plants virtually destroyed by these black bugs that have been eating the leaves and pooping all over it. I am attaching a picture for your reference. I am sorry that some of these photos are a big blurry.

I actually caught one of the bugs in pooping action. What can I do about these things? Thanks so much!
From Pennsylvania

Hi Rebecca,
This is a Margined Blister Beetle,
Epicauta funebris. Sorry, we cannot provide any extermination advice. We remove pests on our tomatoes by hand.

Letter 17 – Margined Blister Beetle

Subject: Beetles skeletonizing my hostas
Location: St. Louis, MO
July 14, 2012 5:15 pm
Hi bugman! My hostas are being skeletonized by what looks to me like a blue firefly (lightning bug, for keyword searching).
At first I thought slugs but the hostas are *covered* in these bugs and they also appear to be dropping some eggs or something on the leaves as well.
Any help would be appreciated!
Signature: baffled by beetles

Margined Blister Beetle

Dear baffled by beetles,
You are not as baffled as your signature indicates because you did deduce that this is a beetle.  More specifically, it is a Margined Blister Beetle,
Epicauta funebris, which you can verify on BugGuide

What you believe to be “eggs or something” are the droppings of the beetles which as your letter indicates are voracious eaters.  You should exercise caution with Blister Beetles.  Though they do not bite nor sting, they do release a compound known as cantharidin from their joints that can cause blistering in human skin.

Droppings from Margined Blister Beetles

Thanks! I didn’t expect a reply so soon. I did look at quite a few
photographs and figured it had to be a beetle based on those but just
couldn’t find the right category to browse. I appreciate the very
timely response!
~baffled by beetles

Letter 18 – Master Blister Beetle

Beetle ID
I was hiking with friends in the desert the other day in Baja and we came across these beetles on a margarite bush (incensio in Spanish). They had black wings. Underneath, they were red-orange with black dots. Very pretty. Thank You!

Hi Lynn,
Your beetle is Lytta magister, the Master Blister Beetle. According to BugGuide: “Pressing or rubbing adult blister beetles may cause them to exude some of their hemolymph (“blood”), which contains Cantharidin. Cantharidin causes blistering of the skin, thus the name blister beetle.”

Letter 19 – Master Blister Beetle

What is this bug?
This photo was taken on the hood of my truck. It is approximately 1 inch long from the front of its head to the end of its body. I saw this in Southern California on May 30, 2008 at 3:45pm. What is it?

Hi Randy,
This is a Master Blister Beetle, Lytta magister. Adults are active in the spring in the Mojave and Colorado deserts.

Letter 20 – Another Master Blister Beetle

unidentified cool bug from johua national park
I think it’s some kind of beetle but am not sure. I know I’ve never seen any like it. Anyway I’ll share naming rights with you if it’s never been seen before.
Henry Hagemeyer

Hi Henry,
We believe the location of your photo is Joshua Tree National Park, and this is the second image of a Master Blister Beetle we received today.

Letter 21 – Master Blister Beetle

I found this beetle at the base of an aloe plant (Mesa,AZ). Can you please identify it and is it harmful to plants? Thank you,

Hi Carol,
This is a Master Blister Beetle, Lytta magister. Adults feed on plant tissue from desert plants and larvae prey on grasshopper eggs in the soil. This species is also known as the Arizona Blister Beetle.

Letter 22 – Master Blister Beetle

Arizona Blister Beetle?
I took this several years ago in the middle of the Mojave Desert – miles from anything! I think it’s an Arizona Blister Beetle. He (?) was just sitting there on his butt eating lunch.
John Stevens
Palmdale, CA

Hi John,
BugGuide lists this species, Lytta magister, as having the common name Master Blister Beetle.

Letter 23 – Master Blister Beetle

What’s that bug?
My husband found this bug recently in Needles, NV. Any idea? We think it’s cool! We love bugs! Thanks,

Hi Michele,
Your strikingly beautiful beetle is a Master Blister Beetle, Lytta magister.

Letter 24 – BUG OF THE MONTH APRIL 2009: Master Blister Beetle

Long, bright orange beetle with black wings
Sun, Mar 29, 2009 at 4:12 PM
I found a bunch of these orange and black beetles while airsofting in Arizona and I am not exactly sure what they are. They were in large groups in the grassy areas crawling on eachother. Is it a type of desert beetle?
Arizona, United States

Master Blister Beetles
Master Blister Beetles

Every year in the spring, we get numerous inquiries about Blister Beetles, especially from the desert areas of the Southwest. When Blister Beetles appear, it is often in prodigious numbers, and then suddenly, they vanish. This is a Master Blister Beetle, Lytta magister. It is well represented on BugGuide.

This is one of the largest of the Blister Beetles. The adults eat foliage, flowers, pollen and fruit, and according the BugGuide: “Larvae live in bee nests.” Some species of Blister Beetles feed on grasshopper eggs. The beetles in the family Meloidae are known as Blister Beetles because they secrete hemolymph (blood) from their joints when handled, and the hemolymph contains cantharidin which can cause blisters. A European relative is the infamous Spanish Fly. Congratulations on having your letter and image chosen as our Bug of the Month for April 2009.


Letter 25 – Master Blister Beetle

Orange and Black Beetles
Tue, Jun 2, 2009 at 9:13 PM
Found these just north of Scissors Crossing in mid-April. I haven’t been able to figure out what they are and was hoping you would have better luck.
David Ellzey
San Felipe Hills, Southern California

Master Blister Beetle
Master Blister Beetle

Hi David,
Had you checked out our website in April, you would have found that the Master Blister Beetle, Lytta magister, was our featured Bug of the Month for April 2009.

Letter 26 – Master Blister Beetle

Blister Beetle in Anza Borrego
March 27, 2010
Hi Bugman! I wanted to share these pictures of a Blister Beetle we saw 3/27/10 in Anza Borrego desert state park. It was really pretty and was running along a patch of sand.
Anza Borrego State Park, Southern California

Master Blister Beetle

Hi Laura,
We need to finish our book by April 1, and we hope to be able to escape to the desert for at least a day trip before Spring Break ends, and perhaps we will encounter some Master BLister Beetles, Lytta magister, while we are there.  We suspect the rain pattern this season might produce a spectacular profusion of desert vegetation, which may also result in more insects than normal.

Letter 27 – Master Blister Beetle

Is this a Longhorn beetle (Phymatodes amoenus)?
March 29, 2010
I was hiking in the mountains in Ludlow, very rural area and came upon a small migration of these beetles. Some were tail to tail. They just seemed to pose on rocks and were in an area about 3 feet by 6 feet. What are these?
I don’t have a preference
Ludlow, California.

Master Blister Beetle

Dear without a preference,
This is the third photo we have posted in the past week of a Master Blister Beetle, Lytta magister, and we are considering making it the Bug of the Month for April.  It is found in the spring in deserts of Arizona and California as well as Mexico, Nevada and Utah.

thank you so kindly. I hope you have a beautiful day.

Letter 28 – Master Blister Beetle

Flying Insect
April 29, 2010
These bugs are all over Thunderbird park. They fly and their wings are noisy. They are over an inch long. They are bright red and black. There are a lot of them around the yellow wild flowers. I would love to know more about them.
Thunderbird Park–Glendale, AZ

Master Blister Beetle

Hi Marianne,
The Master Blister Beetle, Lytta magister, is sure a beautiful beautiful beetle, but don’t touch.  Blister Beetles secrete a compound known as cantharidin that can cause the skin to blister.

Letter 29 – Mating Master Blister Beetles

Red Head Beattle or Roach?
Location: Phoenix, Arizona (U.S. Southwest)
April 9, 2011 9:46 am
What is it? and why did I see a lot of pairs joined at the rear?
Signature: Gary -Phoenix Az.

Master Blister Beetle

Hi Gary,
You have Master Blister Beetles,
Lytta magister, in your area.  Adults appear in the spring, and the reason so many of them are joined in pairs is that they are mating.  Blister Beetles have complicated life cycles, and the larvae live in the nests of native bees.  Blister Beetles should be handled with care as they are capable of exuding a compound that will cause blistering of the skin.

Mating Master Blister Beetles

Letter 30 – Master Blister Beetle

Head of an ant and body of a beetle!
Location: Northern Oregon
September 19, 2011 10:49 am
My friend took this up at her work in Northern Oregon…we have no idea what it is and I’ve looked through a bunch of pictures trying to find it! Any ideas?
Signature: Laura

Master Blister Beetle

Hi Laura,
We are guessing this is not a recent photo.  Most of the photos we receive of Master Blister Beetles,
Lytta magister, arrive in the spring, and they also hail from the deserts of California and Arizona, though we have received a submission from Washington.  We like to utilize the range data on BugGuide, but alas, the site is currently unavailable.

Thank you for your help! The photo was recent- she took it yesterday, but a friend suggested it was a fire-colored beetle (Pyrochroid) and after looking a pictures online- it does resemble many of them.

Not sure if that’s it or not, but it does look like it! And I’m not sure what time of year they normally come out but she saw it September 19th 2011. Thanks again for your response! Y’all have a great site!

We are certain that this is a Master Blister Beetle and NOT a fire colored beetle.

Letter 31 – Master Blister Beetle

Subject: Good bug or bad bug
Location: Apache Junction AZ
March 29, 2016 5:33 pm
This insect was found in Apache Junction AZ.
What is it?
Signature: Wondering

Master Blister Beetle
Master Blister Beetle

Dear Wondering,
When it comes to bugs, the adjectives good and bad are quite relative, and this Master Blister Beetle is no exception.  Master Blister Beetles, according to BugGuide, appear in late winter in the states of the Southwest.  Like other members of the genus, Master Blister Beetles should be handled with caution or not at all because according to BugGuide

“Pressing, rubbing, or squashing blister beetles may cause them to exude hemolymph which contains the blistering compound cantharidin. Ingestion of blister beetles can be fatal. Eating blister beetles with hay may kill livestock. Cantharidin is commercially known as Spanish Fly.”

Letter 32 – Spring in the Desert: Master Blister Beetle

Subject: Fascinating Winged Creature
Location: Fall Canyon Trail, Death Valley, Calif.
April 4, 2016 3:41 pm
Yesterday, while hiking the Fall Canyon Trail in Death Valley, my eyes bugged out when I crossed paths with this incredible creature that looked like a giant winged ant scrambling over the gravel in front of me.

A cursory search of “strange insects of Death Valley” and a dive through my usually trusty Laws Field Guide proved fruitless so that is why I am compelled to bother you in hopes you can solve the mystery. For what it’s worth the insect appeared to be approximately two inches long.
Signature: W. Campbell

Master Blister Beetles
Master Blister Beetles

Dear W. Campbell,
Each spring, nature lovers who flock to the deserts of the southwest to see desert wildflowers in bloom send us magnificent images of Master Blister Beetles to identify.

Letter 33 – Master Blister Beetle

Subject: Many on Pinnacle Peak hiking trail–Scottsdale, AZ
Location: Scottsdale, AZ
April 11, 2016 4:51 pm
Hi Bug People,
Ran into many of these on my hike… What is it?
Signature: Sue

Master Blister Beetle
Master Blister Beetle

What this is Sue, is one of our favorite springtime sightings from Arizona and California, a Master Blister Beetle.

Letter 34 – Master Blister Beetle

Subject:  Beetle
Geographic location of the bug:  Southern California
Date: 03/25/2019
Time: 12:00 PM EDT
Your letter to the bugman:  I work as security at a school in 29 palms California and I saw this interesting beetle and tried to find out what it was but couldn’t. So here’s some pictures you tell me what it is. I don’t know
How you want your letter signed:  Clint Marshall

Master Blister Beetle

Dear Clint,
Thanks for writing back to us to inquire on the status of your identification request.  We went back through unanswered mail and located your stunning images of a Master Blister Beetle

We posted our first images last week of the magnificent Master Blister Beetle, though in fact your images were submitted more than two weeks earlier.  Please excuse our lag time in responding.

Master Blister Beetle
Not a problem. This is the first time I have ever seen one of these in my 40 years plus living in 29 Palms. Thanks for replying. You can do what you want with the images.

Letter 35 – Nuttail’s Blister Beetle and Mirid Plant Bug

Nuttall’s blister beetle and true bugs
Thu, Jun 18, 2009 at 6:33 AM
Hi Lisa Anne and Daniel, when I took this photo I was focused on the blister beetle. But I am now intrigued by the true bugs which I am unable to identify. Can you?
Thanks so much.
Pine Mtn, west of Casper, WY

P.S. Nuttall’s
Thu, Jun 18, 2009 at 6:58 AM
Sorry, I know better. They are on Golden Banner (Thermopsis rhombifolia).
Pine Mtn

Nuttail's Blister Beetle and unknown Plant Bug
Nuttail’s Blister Beetle and unknown Plant Bug

Hi Dwaine,
Thanks so much for sending us your photo of Nuttail’s Blister Beetle. Lytta nuttalli. We believe the Hemipteran in the photo is a Plant Bug in the family Miridae. We looked through many photos on BugGuide, and we believe your bug most closely matches a posting of the genus Hadronema.

Interestingly, there is a photo posted to BugGuide of a Plant Bug in the same subfamily, Orthotylinae, Aoplonema nigrum, that is associated with a Blister Beetle. We will contact Eric Eaton to see if he agrees with our identification. Perhaps the plant bugs gather the blistering agent, cantharidin, as a defense mechanism.

Update: from Eric Eaton
The swamp milkweed beetle ID is right on.  I don’t have the time at the moment to research the plant bug beyond family level, and that is also correct (Miridae).

Letter 36 – Probably Nuttall’s Blister Beetle

Montana Beetle?
April 6, 2010
I photographed this insect, and some others, at about 8000 feet in central Montana in a Lupine field. Some were mating. They were quite large, I’m guessing about 1.5 inches. This was in July 2009. They were strikingly beautiful in the sunlight, and I would love to know what they were. And love your website too, by the way. Thank you.
Montana Hiker

Nuttall’s Blister Beetle, we believe

Dear Montana Hiker,
This is a Blister Beetle in the genus Lytta, possibly Lytta cyanipennis based on images posted to BugGuide, or more likely, Lytta nuttalli, commonly called Nuttall’s Blister Beetle, also pictured on BugGuide.

Letter 37 – Mating Nuttall’s Blister Beetles

What’s this bug?
Location:  Western North Dakota
August 5, 2010 6:28 pm
This bug was found in western North Dakota on some leaves. I think it’s a beetle, but don’t know for sure.

Mating Nuttall’s Blister Beetles

Hi Jason,
These are mating Blister Beetles, and based on images posted to BugGuide, they appear to be Nuttall’s Blister Beetles,
Lytta nuttalli.

Letter 38 – Nuttall’s Blister Beetle

Subject: Iridescent Beetle
Location: Lac Pelletier Regional Park, Saskatchewan
July 3, 2013 9:38 am
Thought you might like to have these photos I took of Nuttall’s Blister Beetle. I didn’t know what they were at the time, but since found ID on the internet. There were a lot of them feeding and mating. Photo was taken June 30, 2013 around midday of a scorching hot day at Lac Pelletier Regional Park, south of Swift Current Saskatchewan.

They are so beautiful you’d like to wear them – now that I know they can secrete a blistering compound, I’m glad I didn’t decide to tie a string on one and attach it to my lapel!
Signature: Qnina

Nuttal's Blister Beetle
Nuttal’s Blister Beetle

Dear Qnina,
Thank you for submitting your images of Nuttal’s Blister Beetles.

Nuttal's Blister Beetles
Nuttal’s Blister Beetles

Letter 39 – Nuttall’s Blister Beetle from Canada

Subject: What is this?
Location: Kindersley, Saskatchewan, Canada
August 15, 2014 9:15 pm
Found this beetle (?) dying on my concrete this evening. I live in Kindersley, Saskatchewan. It has a brilliant metallic green body, head of a wasp and dusty purple shell that does not run the full length of it’s body. It has been quite warm and humid lately for August and I was not sure if that is why it was around because I have never seen one before.
Signature: Stacey Herbert

Blister Beetle
Blister Beetle

Dear Stacey,
This is a Blister Beetle in the family Meloidae, and we generally prefer a dorsal view for identification purposes, but your description that includes the coloration has us relatively confident that your individual is Nuttall’s Blister Beetle,
Lytta nutalli, which is frequently reported from Canada.  Blister Beetles should not be handled as they often secrete a compound known as cantharidin that is known to cause blistering in human skin.

Letter 40 – Nuttail’s Blister Beetle

Subject:  Metalic Green Beetle
Geographic location of the bug:  North Central Colorado Foothills
Date: 07/19/2018
Time: 08:40 AM EDT
Your letter to the bugman:  Dear Bugman,
This awesome little beetle ended up flying into my face while I was our for a hike at one of our foothills parks.  I have never seen anything like this little guy before.  I am hoping you can shed some light for me.
How you want your letter signed:  With a pen… or pencil… it’s all good.

Nuttail’s Blister Beetle

Thanks to this BugGuide image, we are confident that this is Nuttail’s Blister Beetle, Lytta nuttalli, a species with much color variation.  According to BugGuide:  “Adults feed on legumes.” 

You were lucky when you encountered this Nuttail’s Blister Beetle because physical contact with Blister Beetles should be avoided as they can secrete cantharidin, a compound known to cause blistering in human skin.

Letter 41 – Nuttail’s Blister Beetle

Subject:  Unknown beetle
Geographic location of the bug:  Lostwood national wildlife refuge North west North Dakota
Date: 07/13/2019
Time: 05:23 PM EDT
Your letter to the bugman :  Unable to find this beetle in any North Dakota books.
How you want your letter signed:  Thank you

Nuttail’s Blister Beetle

This is a Blister Beetle in the family Meloidae, and based on this BugGuide image, it appears to be Nuttail’s Blister Beetle.  According to BugGuide:  “Adults feed on legumes, other forbs.”

Nuttail’s Blister Beetle

Letter 42 – Nuttall’s Blister Beetle

Subject:  Unidentified beetle
Geographic location of the bug:  Winnipeg mb Canada
Date: 08/07/2019
Time: 06:32 PM EDT
Your letter to the bugman:  I took this photo June 24,2019, there is a interpretative centre where I took the pic with research material and I looked online and cannot identify it, The closest I found was a Festive Tiger Beetle but no where close enough. I spoke to an entomologist still no luck.   Any assistance will be appreciated. Thank you
How you want your letter signed:  Steve Baxter

Nuttall’s Blister Beetle

Dear Steve,
Your images are positively gorgeous, and they beautifully represent this Nuttall’s Blister Beetle,
Lytta nuttalli, which is pictured on BugGuide.  According to BugGuide:  “Adults feed on legumes” and the flower in your image does look to us like a legume.  Blister Beetles in the family Meloidae should be handled with caution as many species can exude hemolymph containing the blistering compound cantharidin.  The infamous aphrodesiac Spanish Fly is produced by crushing the bodies of a Spanish Blister Beetle.

Nuttall’s Blister Beetle
Thank you for the information. I have recently retired and bought a new camera and a macro lens and discovered  there really are a lot of interesting insects. I am enclosing a couple interesting photos, 1 a great picture of a Monarch butterfly, and the second which I didn’t notice the ladybug is chowing down the aphids on the plant. Thanks again for your assistance.


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    Bugman aka Daniel Marlos has been identifying bugs since 1999. is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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15 Comments. Leave new


    You are one of the WINNERS

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  • The species name for this blister beetle is Lytta magister. The are often seen in large aggregations on flowers in the desert in spring. They are common throughout the Mojave Desert.

    L. Saul

  • I photographed Master Blister Beetles feeding (and mating) on rabbitbrush flowers in Eastern Idaho on 9/10/2011. Their range is definitely not just Mojave and Colorado deserts as indicated on BugGuide and they are active here in the fall, obviously. Perhaps they have been poorly documented or have expanded their range?

    • Thanks for your perspective. Should you decide to send us your photos, please use the normal submission form and title the email Master Blister Beetles from Idaho.

  • I see these here in Arizona this time of year,. The pics I sent are from 2011 and saw a couple today. Couldn’t get good pics though

  • I have these margined blister beetles in my garden for the first time ever. I have grown tomatoes every year and never seen this pest. They are swarming my tomatoes and stripping the foliage. My tomatoes are staked with steel fence posts and banging on the posts vibrates the whole plant and they fall off. However they seem quite happy to invade the mulch below to hide. Hand picking is not achieving control as a new swarm soon arrives. What are the effective and practical control methods for these. I would like to save this year’s tomato crop and also prevent the problem in the future. That probably means two different control methods, and I need to know methods in both of those categories. So far they have not seemed to attack any of the other crops in my garden. We never found any on the potatoes which are the same “family” as potatoes and that garden plot is separate bot only 25 feet away.

    • We do not provide extermination advice. If you figure out a good method, please write back so that the information can help our readership.

  • Greg Gauthier
    March 28, 2015 8:43 pm

    I saw close to 30 of these Master Blister Beetles today in the Colorado Desert in the Mule Mountains mating and flying and seemingly trying to attack me as I ran from them. They were frenzied and aggressive.

  • I have pictures and video of them mating. Also pictures of 3 of them in a pile cleaning eachother I believePlease email me at.

  • I located one in Mojave desert; state of Sonora, Mexico

  • Susan Hallett
    April 4, 2019 8:45 pm

    We live in north Phoenix and currently have an infestation of these beetles – hundreds and hundreds of them. Many are mating or have died. They are feeding on our brittlebushes during the day. We have called pest control to help us get rid of them.

  • John Loreaux
    June 18, 2020 5:59 pm



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