Are Monarch Butterflies Poisonous? Unraveling the Mystery

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Monarch butterflies are one of the most recognized and loved insects in North America. But are monarch butterflies poisonous? We take a look in this article.

These beautiful creatures play a crucial role as pollinators and are an important food source for birds, small animals, and other insects.

Are Monarch Butterflies Poisonous

Interestingly, the vivid markings of the monarch butterfly (Danaus plexippus) serve as a warning to predators, signaling “Poison!” The reason behind this warning lies in their diet during their caterpillar stage.

Monarch caterpillars feed exclusively on milkweed plants, which contain cardiac toxins that are poisonous to most vertebrates but not harmful to the caterpillars themselves.

As a result, monarch butterflies become poisonous to potential predators due to their consumption of milkweed toxins. This natural defense mechanism helps protect them from harm and ensures the survival of their species.

Monarch Butterflies and Milkweed

Milkweed’s Role in Monarch Lifecycle

Monarch butterflies are known for their dependence on milkweed plants. The female monarchs lay their eggs on milkweed, which then serves as the primary food source for the caterpillars (larvae).

Different milkweed species grow across regions, but most of them are consumed by monarch larvae.

Toxicity in Milkweed

Milkweed contains a group of chemicals known as cardiac glycosides. These substances can be toxic. When monarch caterpillars feed on milkweed, they ingest these toxins.

Monarch Caterpillars and Milkweed Toxins:

  • Caterpillars become poisonous as they store toxins in their bodies
  • Predators that eat caterpillars suffer from vomiting, diarrhea, and other health issues
  • Toxicity increases as caterpillars grow and consume more milkweed

As the caterpillars grow into adult butterflies, they retain the toxins in their bodies. This makes monarch butterflies poisonous to certain predators.

Pros and Cons of Milkweed Toxins for Monarch Butterflies:

Pros

  • Protection from predators due to toxic chemicals
  • Unpalatability makes them less appealing to potential predators
  • Bright orange and black colors serve as a warning sign to predators

Cons

  • Consuming too much toxin may have potential harmful effects on the butterfly itself
  • Some predators have developed resistance to the toxins
  • The need for milkweed as a host plant can limit the butterfly’s habitat range

Monarch Butterflies vs. Other Butterflies:

FeatureMonarch ButterfliesOther Butterflies
Host PlantMilkweedVarious plant species
ToxicityPoisonous due to milkweed toxinsMay or may not be poisonous
ColorBright orange and black as a warningVaries depending on the species

In summary, monarch butterflies become poisonous primarily due to feeding on milkweed plants throughout their lifecycle. The toxins they accumulate offer protection from predators and contribute to the iconic appearance of these butterflies.

Are Monarch Butterflies Poisonous?

Effect on Predators

Monarch butterflies (Danaus plexippus) are known for their striking orange color and beautiful patterns.

This vivid appearance serves as a warning to predators, as the insects are indeed poisonous.

They accumulate toxins known as cardenolides from their primary food source, milkweed plants (Asclepias).

These cardiac glycosides can cause vomiting, muscle contractions, and even heart failure in some predators.

Birds, small animals, and other insects that feed on monarchs learn to avoid them due to their unpleasant taste and toxic effects.

Some common predators that are deterred by the monarchs’ toxicity include:

  • Birds
  • Mice
  • Lizards
  • Ants

Caterpillar to Adult: Increasing Toxicity

The process of accumulating toxins begins when monarchs are still in their caterpillar stage. Caterpillars feed exclusively on milkweed, ingesting toxins as they consume the plants’ leaves.

As they grow and eventually form a chrysalis, the toxins remain in their bodies.

During the metamorphosis into adult butterflies, the concentrations of cardenolides increase, making the adult monarchs even more toxic than their caterpillar counterparts.

Below is a comparison of the toxicity levels in monarch caterpillars and adult butterflies:

StageToxicity LevelDefense
CaterpillarModerateWarning markings
AdultHighVivid colors

In conclusion, the poisonous nature of monarch butterflies plays a vital role in their defense strategy against predators.

By accumulating toxins during their development from caterpillars to adults, they send a clear warning signal to potential predators and reduce the chances of becoming prey despite being a beautiful and highly visible species.

Impact on Ecosystem and Other Animals

Relationship with Humans and Animals

Monarch butterflies play a vital role in the ecosystem as pollinators, assisting in the reproduction of flowering plants.

Their striking orange wings with black borders and white spots make them recognizable and cherished by people.

Some animals, like frogs, might attempt to prey on monarchs, but they are generally unpalatable due to toxins they acquire from milkweed plants, their primary food source.

Monarchs’ vivid colors serve as a warning sign to potential predators.

Monarch

Migration and Range of Monarch Butterflies

Monarch butterflies are famous for their incredible migration, covering thousands of miles from southern Canada to central Mexico.

Their range spans North America, including the United States, southern Canada, and Mexico, with some populations also found in Hawaii, South America, Australia, and India.

There are two main populations of monarchs: the eastern and western.

The eastern population ranges from the Rocky Mountains to the Atlantic Ocean and migrates to central Mexico for the winter, while the western population primarily inhabits areas west of the Rockies, such as California, with some traveling to southern California or Mexico during winter.

Eastern PopulationWestern Population
Rocky Mountains to the Atlantic OceanWest of the Rocky Mountains, including California
Migrates to Central Mexico in winterSome migrate to Southern California or Mexico in winter

During their migration, monarchs face numerous challenges, including:

  • Habitat loss: both in their breeding grounds and along their migration routes
  • Pesticides and herbicides: affecting milkweed plants and other nectar sources
  • Climate change: altering weather patterns and affecting the availability of food sources

To support monarch butterflies, humans can take steps like planting native milkweed species, reducing pesticide and herbicide use, and conserving habitats critical to their life cycle.

Conservation Efforts and Challenges

Endangered Status and Population Decline

Monarch butterflies, known for their incredible migration, have experienced a significant population decline1.

The Eastern migratory population has decreased by around 80%2. Various factors contribute to this, including habitat loss and environmental changes. Monarch butterflies go through several life stages, such as:

  • Egg
  • Larva
  • Pupa
  • Adult

Each stage faces its own challenges, and the conservation of all life phases is essential for the species’ survival3.

Growing Monarch Caterpillars

Climate Change and Monarch Habitats

Climate change poses another challenge to monarch butterflies, as it can directly impact their habitats.

Monarchs have a close connection to their breeding grounds, specifically in South America. As temperatures rise and weather patterns change, so do the conditions of these critical habitats.

Pros of conserving monarch habitats:

  • Ensures survival of all life stages
  • Protects an endangered species

Cons of conserving monarch habitats:

  • Requires resources and coordinated efforts

Comparison between two main monarch populations:

PopulationRegionDecline (%)
EasternNorth America802
Western (Lesser)South Americaunknown

Conservation efforts must consider various factors such as climate change and habitat loss to be effective. Endangered status of monarch butterflies calls for continued research and international cooperation to protect this iconic species.

Footnotes

  1. Plight of the Monarch

  2. Monarch Butterflies 2

  3. Monarch Butterfly FAQs

Conclusion

To sum up, the captivating world of monarch butterflies encompasses not only their renowned beauty and remarkable migration but also their intriguing poisonous nature.

The presence of cardiac glycosides in milkweed-enriched diets grants them an unpalatable defense mechanism against predators.

While the toxicity level varies, their vibrant warning colors serve as a universal signal, deterring potential predators from making fatal mistakes.

Understanding the intricacies of this toxicity adds depth to our appreciation of these delicate yet resilient creatures and underscores the importance of conserving their habitats for future generations to admire and learn from.

Reader Emails

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

Letter 1 – A Monarch Metamorphosis

Monarch Chrysalis
Monarch Chrysalis

Danaus plexippus
July 22, 2009
Last year my granddaughter wanted to keep a monarch caterpillar. I told her it was OK but she had to let it go when it was ready. Here are the photos. Hope you enjoy them as much as I. Not looking for a reply.
Terry Sincheff
Mound, MN

Monarch Chrysalis Hatching
Monarch Chrysalis Hatching

Hi Terry,
We are positively thrilled to post your images of a Monarch Butterfly metamorphosing.

Monarch Emerged
Monarch Emerged

Letter 2 – Brown Pansy Butterfly from South Africa and Monarchs

Subject: Brown Commodore Butterfly
Location: Marloth Park, South Africa
April 22, 2014 10:58 am
Thank you, Bugman for all you help!
I’m happy to share some photos of recent butterfly findings.

This one is the Brown Commodore Butterfly found in Marloth Park, South Africa on April 20, 2014.

This and other fabulous insects can be found on my blog at http://www.travelsandtripulations.com/2014/04/21/the-wildlife-of-marloth-park-south-africa/
Cheers,
Signature: Kenda

Brown Pansy
Brown Pansy

Hi Kenda,
We tried finding a link online to your Brown Commodore, and we found it listed as a Brown Pansy,
Junonia natalica natalica, on Butterfly Valley.  It is also called a Brown Pansy on BioDiversity Explorer as well as on ISpot and iGoTerra

The Butterflies of Kruger National Park also calls it a Brown Pansy and we learned it:  “prefers the shadows of riparian forest and woodland found along waterways in the KNP.” 

Common names can be confusing, so we are curious where you found this lovely Nymphalid called a Brown Commodore.

April 22, 2014
Hello Daniel,
Very interesting!  Attached is a PDF I found online, and I’ve been using it to name the butterflies I’ve been photographing.

That’s where II found the name “Brown Commodore” on page 80. I was unaware of the other resources, but they seem more in-depth. Thanks for passing that along


Given your passion for bugs, I wonder if you’ve ever been to the Monarch Sanctuaries in Mexico (Michoacan). I’m very passionate about the Monarchs and used to volunteer at Natural Bridges in Santa Cruz (an overwintering site for Monarchs).

We visited Michoacan last year while living in Mexico (there’s a post called Mariposas Monarcas), and it is heavenly. While we were there, we met Lincoln Brower, a leading authority on the Monarchs. He just happened to be doing research while we were there – amazing!

He talked to us about the decline of the Monarchs – the usual suspects: deforestation (habitat destruction) due to logging (legal and illegal) and of course, human activity like people spraying their gardens (Roundup and other products by agrochemical companies with Monsanto being the most evil IMO) or pulling milkweed.

Monarchs only lay eggs on milkweed (she will die looking for it), so the world needs to know that we need more milkweed. Healthy milkweed. And no more toxic spraying in the gardens. It’s not only killing Monarchs who nectar on other flowers but other insects. They’re all vital!
Cheers,
Kenda

Letter 3 – Bug of the Month November 2014: Monarch Migration

Subject: Monarch Migration
Location: Coryell County, Texas
October 28, 2014 9:48 pm
Hello, this isn’t a usual inquiry in that I’m quite sure that these are Monarch Butterflies.
I’ve never been able to photograph one before, but today they were all over the yard.

I’ve often seen them fly past our yard, usually quite high above the ground during migration times, but today many stopped to drink from our newly-watered lawn. It was incredible.


I haven’t seen so many Monarchs since I was six years old, in Illinois, and clouds of Monarchs dashed south ahead of a severe cold front.
So beautiful!


Here is a link to recent “clouds” of Monarchs in the news: http://goodnature.nathab.com/are-they-clouds-of-monarchs-mysterious-unidentifiable-blobs-spotted-by-radar-over-the-midwest/
Thank you and best wishes.
Signature: Ellen

Monarch
Monarch

Hi Ellen,

There has been much talk lately of diminishing populations of Monarch butterflies, and this year we observed many more Monarchs in our garden than we have ever seen in Los Angeles.  It seems populations might be increasing across the country.  Thanks for this newsworthy posting. 

It must have been a spectacular sight.  We took a bit of creative license with our most recent Bug of the Month posting of a pair of mating Wheel Bugs by designating their month as Halloween, which frees us up for a November Bug of the Month, and your submission is an excellent choice.

Monarch
Monarch

Subject: Monarch Migration, Part 2
Location: Coryell County, Texas
October 30, 2014 2:04 pm
Hello, and thank you so much for your reply.
I’m sending another few photos of the Monarchs in our yard, and an additional link to the Fall of 2014 migration news.

This link adds up-to-date migration news and photos as they are reported. The great news is that observers are currently seeing a large migration.
Sending highest regards.
http://www.learner.org/jnorth/monarch/News.html
Signature: Ellen

Male Monarch
Male Monarch

Hi again Ellen,
The image of the male Monarch in flight (notice those scent patches on his lower wings) is a nice addition to the images you sent earlier.  Thanks for the additional link.

Letter 4 – California Mantis eats Monarch and bites off head of her paramour

Female California Mantis eats Monarch
Female California Mantis eats Monarch

Subject: Preying Mantis: eat, prey, love
Location: South Pasadena, CA
October 11, 2014 6:49 pm
Hello Daniel. Although I have a good population of mantises and monarchs, these were unusual sights for me.

Only time I’ve ever seen a mantis eat a monarch, and only the second time I’ve seen the headless mating. This was last month, within the same week, and I think the same female mantis.
Signature: Barbara

Mating California Mantids with headless male
Mating California Mantids with headless male

Hi Barbara,
We get numerous wonderful submissions each day, but your submission with its excellent images is one of the best we have received in quite some time. 

We believe these are native California Mantids, Stagmomantis californica, and you can compare your female to this image on BugGuide.  The headless mating is is quite some documentation.

Letter 5 – Bug of the Month December 2012: Early Instar Monarch Caterpillars

Ed. Note:  November 30, 2012
If you are lucky enough to live in a warmer climate in North America, you may find Monarch Butterflies or Caterpillars in December.  Monarchs are most likely flying in South America and Central America right now. 

This migratory species is one of the most loved of all butterflies and we hope you enjoy these marvelous images of very young Monarch Caterpillars from Hawthorne California that our loyal reader Anna has supplied for us. 

Read more about Monarchs on the Nature Works website.  You might also think about planting milkweed in your garden to help support populations of Monarch Butterflies.

Subject: Daniel – Monarch Butterfly Caterpillars
Location: Hawthorne, California
November 26, 2012 4:16 pm
Hi,
Just wanted to update you on the Monarch caterpillars in the back. They’re on to solid food now and it’s much easier to find/photograph them.

Hopefully our warm weather holds, as I counted eight this morning in just a few minutes!
Signature: Thanks, Anna Carreon

Early Instar Monarch Caterpillar

Hi Anna,
What did they eat before the “solid food” which we suspect means the leaves of the Mexican milkweed you grow in your garden. 

What do they eat after the egg shell.  In Elyria Canyon Park they seem to eat the flowers first and then move to the leaves of Indian Milkweed.  We love your continuing saga on Monarchs.  Have these Monarch hatchlings molted yet, meaning are they first or second instar?

Five or Six Day old Monarch Caterpillar

Updates
Hi Daniel,
They were piercing the seed pods (rather than eating them from the top down as they did last year when they were older), so I can only think that they must have been drinking liquid from the pod(?) 

They did eat their egg shells.  I don’t notice them eating the flowers, though.  They went straight from the Mexican milkweed pods to the leaves themselves.  I haven’t yet noticed any molting, but will check later this morning.
Anna

November 28, 2012
Daniel,
I did notice today that they are sprouting antennae.  Hope this is helpful.
Anna

Growing Monarch Caterpillars

Thanks for all the additional information Anna.  We are continuing to update your posting.

Update:  November 29, 2012
Hi Daniel,
It’s a bit wet out this morning, so I did not get a chance to spend as much time out back as in previous days.  Today’s count is four, yesterday’s was 12.  I’ve been watching some videos of Monarch caterpillars molting at You Tube and also some time reading a bit about the different instars. 

I think the caterpillars in the photo attached are second instar.  I’m no expert, and it is wet out there, but I think the one on the left may have just molted.  Their antennae are definitely longer today than yesterday when they were just little horns.  Waste not, want not, I’ve read that they eat their old skin. 

I’ll check a little later on to see if that bit of junk just below the caterpillar on the left is gone.
Anna

Second Instar Monarch Caterpillars

Thanks Anna,
It is time to make this posting a feature.

Update:  November 30, 2012
Hi Daniel,
Here are today’s photos.  It is wonderful that we finally have some measurable rain, but, as a result, the little guys are hiding out further into the milkweed where I can’t find them.  Only counted five this morning. 

Thanks very much for the honoring them with your “Bug of the Month” designation for December 2012!
I haven’t found any concrete evidence of their molting, but will keep looking!
Anna

Monarch Caterpillar

Read More

Letter 6 – Female Monarch Butterflies marked with letter “E”

Subject: Two Female Monarch Butterflies
Location: Naperville, IL
September 6, 2013 6:46 pm
Hi Daniel!
Because I don’t think you have have enough happy Monarch butterflies, here are two more! Both eclosed yesterday morning, and both will soon be on their way to central Mexico.

We ink their wings with the letter E so that we will recognize them in the coming weeks as they flit around our neighborhood, fattening up for their long journey.
All the best to you!
Signature: Dori Eldridge

Monarchs marked with ink
Monarchs marked with ink

Hi Dori,
We are quite curious about your “inking” of the Monarchs you raise.  Do they generally return to your garden?  Do you find them in nearby locations in your area?  Do you have any plans to visit the migration destination in Mexico to try to locate your “offspring?”

Female Monarchs
Female Monarchs

Hi Daniel~
I wish I could claim loftier scientific merit to our habit of marking our Monarchs’ wings, but we do it purely for the joy of identifying one of our “own” in the days and weeks after we release it.

As a matter of fact, we do see again quite often the Monarchs we’ve released – both in our yards and in our neighbors’ yards. Friends even a mile and more away have told me that they’ve spotted one of our “E” butterflies fluttering about their gardens.

I do keep many of their favorite nectar flowers in my yard, and it attracts Monarchs that come for the flowers and stay to lay eggs all over the adjoining milkweed, fueling my summer obsession.

At some point in my life I would love to visit their wintering grounds in the Mexican state of Michoacán, but I don’t have high expectations of ever locating an “E” Monarch among the tens of millions that arrive every October.

If I did, I might just die from the thrill. I understand that Monarchs west of the Rocky Mountains overwinter somewhere in southern California – I may have to start there. Where is it that these Monarchs go? All the best to you!
-Dori

Thanks so much for the update Dori.  Our California Monarchs do in fact gather at over 25 sites along the west coast to pass the winter.  You can read about our California Monarchs on the MonarchLab website.  We have photos of the Pismo Beach site in our archives.

Letter 7 – Female Monarch Butterfly in Mount Washington

Female Monarch discovers butterfly garden!!!
Location:  Mount Washington, Los Angeles, CA
August 6, 2012
Yesterday, late morning, while trying to leave for work, Daniel noticed this female Monarch Butterfly sailing around the area where the native Narrow Leaved Milkweed was planted. 

Seems the girl was more interested in nectaring from the Buddleia than in settling on the milkweed.  Daniel managed to get a few photos before it got too late.  He will be inspecting the milkweed and hoping there is an egg or two to be found.

Monarch

April 22, 2014
Hello Daniel,
Very interesting!  Attached is a PDF I found online, and I’ve been using it to name the butterflies I’ve been photographing. That’s where II found the name “Brown Commodore” on page 80. I was unaware of the other resources, but they seem more in-depth. Thanks for passing that along


Given your passion for bugs, I wonder if you’ve ever been to the Monarch Sanctuaries in Mexico (Michoacan). I’m very passionate about the Monarchs and used to volunteer at Natural Bridges in Santa Cruz (an overwintering site for Monarchs).

We visited Michoacan last year while living in Mexico (there’s a post called Mariposas Monarcas), and it is heavenly. While we were there, we met Lincoln Brower, a leading authority on the Monarchs. He just happened to be doing research while we were there – amazing!

He talked to us about the decline of the Monarchs – the usual suspects: deforestation (habitat destruction) due to logging (legal and illegal) and of course, human activity like people spraying their gardens (Roundup and other products by agrochemical companies with Monsanto being the most evil IMO) or pulling milkweed.

Monarchs only lay eggs on milkweed (she will die looking for it), so the world needs to know that we need more milkweed. Healthy milkweed. And no more toxic spraying in the gardens. It’s not only killing Monarchs who nectar on other flowers but other insects. They’re all vital!
Cheers,
Kenda

Letter 8 – Life Cycle of the Monarch Butterfly

Subject: West Los Angeles sighting – Monarch 1
Location: West Los Angeles
July 6, 2017 8:26 am
Hi Bugman,
Here’s the first set of pictures of Monarchs
Signature: Jeff Bremer

Mating Monarch Butterflies

Dear Jeff,
Thank you so much for sending your gorgeous images documenting the complete life cycle of the Monarch butterfly.  It is going to take us a healthy chunk of time to format all your images and set up the posting properly so we are just starting by posting an image of a mating pair of Monarchs. 

The male is the individual with the open wings, and the female appears to have been tagged because her hind wings have what appears to be an inked marking. 

We can also identify the male, according to BugGuide, because:  “Males have scent-scale patches on hindwings, prominent when wings are open, and just possible to see when wings are folded.”  Over the course of the day, we hope to get all your excellent images added to the posting.

Male Monarch

Hi Daniel,
I don’t have complete life cycles for the rest of the butterflies that have graced our back yard, but I’ll send in what I have.  Regarding the Marine Blue, I can resend them with the other pics.  The ones I sent seemed to have unusual coloring.
By the way, I want to thank you for so graciously accepting my pictures.  It makes me happy to be able to share them.
Jeff

Female Monarch
Nectaring Monarchs
Ovipositing Female Monarch
Monarch Egg
Monarch Caterpillar Hatchling
Monarch Caterpillar
Prepupal Monarch Caterpillar
Monarch Chrysalis
Monarch Chrysalis (adult about to emerge)
Newly Eclosed Monarch
Emerged Adult Monarch
Monarch Nursery

Letter 9 – Mating Monarch Butterflies

image of mating monarch butterflies for Bug Love page
Hi,
I came across “What’s That Bug” yesterday and thought you might be interested in the attached image of mating monarch (?) butterflies. I photographed the pair at Grosse Point Lighthouse in Evanston, Illinois, just north of Chicago.

The butterflies were coupled for quite some time, at rest and in flight. I am curious if you know whether its the male or female that does the flying, or both … or, well, is it true love that keeps them aloft? Thanks for a great site.
Deborah

Hi Deborah,
Thanks for sending in your beautiful image. We are going to speculate on your flight question. The male Monarch Butterfly has a black spot, a scent patch, that is easily visible when the wings are opened.

It is not as obvious on the underwings, but the butterfly in your photo whose wings are outermost appears to be the male. That butterfly would be in a better position to control flight. Our speculation is that the male butterfly controls flying to a greater degree when the pair is coupled, but we might be wrong.

Authors

  • Bugman

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

    View all posts
  • Piyushi Dhir

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

    View all posts
Tags: Monarch Butterfly

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1 Comment. Leave new

  • Hi Amaris, you don t mention whether she seems weak and sickly? If so, it would probably be best to euthanize. If not, you could always try to release her the next time you have a good window of weather. If she can t fly, you could always take care of this female monarch butterfly until she expires. Good luck!

    Reply

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