230-Monarch Rx: The Prescription for Healthier Butterflies

| Care, Podcast

As much as we love watching monarch butterflies fluttering in our gardens and landing on flowers to sip nectar, there is much about monarchs that remains a mystery to both gardeners and scientists. My guest this week, Nancy Lawson, is part of a new citizen science project named Monarch Rx, and she’s here to explain an unexpected way that gardeners can support monarch populations.

Nancy lives in Maryland, where she runs a blog,, and she writes a column for the Humane Society’s magazine, All Animals, on ways that we can be friendlier stewards of land. She also has a book, “The Humane Gardener: Nurturing a Backyard Habitat for Wildlife.” As a naturalist with a background in journalism and an interest in science, Nancy explores how we can work with plants to change the world.


Nancy Lawson

Nancy Lawson is the founder of The Humane Gardener. She writes on how gardeners can reduce conflict with wildlife, and she is working on Monarch Rx, a citizen science research project. (Photo Credit: Ken Koons)


Requirements for Monarch Fitness & Health

Monarch butterflies need nectar plants, especially fall nectar plants like goldenrods and asters, Nancy says. They also require milkweed, the only type of plant that their larvae eat. As monarchs face habitat loss, gardeners can help them by planting more of these types of flowers. Monarch Rx is also uncovering a number of other plants that are important to monarch fitness and health. These plants help the butterflies to live longer and to have greater defenses from predators. As Nancy learned, these plants contain a chemical that is toxic to many butterfly parasites and predators.


Monarch caterpillar eating milkweed

Monarch butterfly larvae exclusively feed on plants in the Asclepias genus. These plants, known as milkweeds, contain chemicals that make the caterpillars and the adults unpalatable to predators. (photo: Amy Prentice)


Unexpected Monarch Behavior

Nancy recalls in June 2019 taking a photo of a monarch butterfly on a white boneset (Eupatorium serotinum). It appeared to Nancy that the butterfly had just landed there to perch, but then through her zoom lens she noticed that the insect was extending its proboscis onto a leaf. Whenever the butterfly was disturbed by a car going by, it would fly around but always come back to the boneset, ignoring the milkweed and other plants.

After 10 minutes of watching and recording the butterfly, Nancy downloaded the videos and took a closer look at what the butterfly was up to. It was using its feet to scratch a leaf. Though most butterflies have chemoreceptors on their feet and antennae, it was thought that monarchs don’t practice leaf scratching behavior. 

After sharing the video to a butterfly group on Facebook, she received a response from Dr. Don Harvey, a retired lepidopterist (someone who collects or studies butterflies and moths) at the Smithsonian Institution’s Museum of Natural History. Don shared a 1983 scientific article on leaf scratching by Michael Boppré, a since-retired professor in Germany who observed that butterflies scratch outward from holes created by flea beetles. Sure enough, when Nancy inspected again she found a flea beetle in the video and holes in the leaves. 

The butterfly was engaging in pharmacophagy — the consumption of plants to acquire beneficial chemicals rather than nutrition. Think of it as going to the pharmacy rather than going to the grocery store, Nancy says. Specifically, the butterfly was after pyrrolizidine alkaloids, known as PAs, in the leaves. The toxin accumulates in the bodies of the butterflies, making them unpalatable to many predators.



Many milkweed butterflies (Daniadae) use PAs as a chemical defense against predators and also synthesize PAs into pheromones for courtship, but it was thought that monarchs were an exception. Monarch courtship behavior includes males chasing the females and pinning them down, Nancy says, though she adds there may be other aspects of courtship behavior that we don’t witness. 

Nancy dove in. She downloaded as many papers by Michael Boppré as she could and learned all there was to know about PA pharmacophagy. She learned that pharmacophagy often involves dried leaves, withered plants and dead plants. Scientists have actually successfully baited butterflies and moths using dried leaves or vials of concentrated pyrrolizidine alkaloids. Some grasshoppers, beetles and flies are likewise attracted to leaves containing PA.

Butterflies and other insects can detect PAs in a range of wildflowers, such as some species in the dogbanes, borage, aster and legume families. 


Butterfly on flower

At first glance, it appears that this male monarch is nectaring. But look closely, and you’ll see that he has actually expanded his proboscis to a cluster of drying flowers while leaving the fresh ones alone. To take PAs up, monarchs apply a fluid to the dried plant parts and then reimbibe it with dissolved PAs. This one gathered PAs from this plant for about an hour in August.
(Photo Credit: Nancy Lawson)


The Most Valuable Flowers for PA Pharmacophagy

It’s well known among gardeners that monarch caterpillars can only eat plants in the Asclepias genus, known as milkweeds. And by eating milkweed, the caterpillars accumulate cardiac glycosides that make them unattractive to predators. Cornell University Professor Anurag Agrawal wrote at length about this relationship in his book Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution,” which he discussed with me on the podcast last year.  

But less is known about what flowers monarchs rely on to gather pyrrolizidine alkaloids. Michael Boppré is trying to find out which flower species are the most important to the monarchs when it comes to PAs.


Butterflies gathering

Numerous milkweed butterflies in other parts of the world engage in PA gathering, a phenomenon that ecologist Michael Boppré has long studied. In Kenya, he observed Danaus chrysippus, Amauris ochlea, and Tirumala petivera at baits made of dry PA-plants (top and lower left) and A. ochlea visiting a dish containing pure PAs (right). But the behavior has been almost completely neglected or forgotten in the study of monarchs. Through the Monarch Rx project, he and Lawson hope to expand knowledge about which plants monarchs are visiting for PAs and under what conditions.
(Photo Credit: Michael Boppré.)


Once Monarch Rx was established to help answer that question, the first respondent was Brice Claypoole, a 13-year-old in Florida who runs a nature and conservation blog, The Kid Who Cares. Brice told Nancy that he observed a monarch scratching dead Joy Pye weed.

The reports kept coming: monarchs on Virginia bluebells (Mertensia virginica) in Michigan and on marble seed (Onosmodium) in Iowa.

In all cases, the plants were dead or dying. This makes sense, as Nancy points out that PAs are not detectable in plants until the cells start to break up, because the PAs are concealed within the cell walls before then.


Late boneset

Late boneset (Eupatorium serotinum) is also a magnet for hairstreaks, common buckeyes, moths, wasps, beetles, flies—and many human neighbors, who often stop in their tracks to inquire about the plant. Though the leaves have an earthy scent, the flowers smell as sweet as roses, especially when grown in masses. In Lawson’s habitat, boneset volunteered in the front garden about 15 years ago and has been sprouting all over the land ever since. Deer and rabbits tend to pass the plants by because of their bitter taste; the same PAs that are so attractive to monarchs can become toxic to mammals over time.
(Photo Credit: Nancy Lawson)


The Possible Link Between PAs and Monarch Eggs

One theory is that monarchs gather PA as a defense against Ophryocystis elektroscirrha, or OE, a parasite that can cause monarchs to be deformed and weakened. The OE spores are most likely to infect caterpillars in their early stages of life.


Male and female butterfly

A male and female monarch visit a withering late boneset (Eupatorium serotinum) that had broken halfway down the stem. PA gathering has long been thought to be largely the purview of males in milkweed butterfly species, but female monarchs have been spotted engaging in the behavior just as frequently in Lawson’s garden. It’s possible that they’re shoring up their defenses to help protect their offspring against the OE (Ophryocystis elektroscirrha) parasite, a protozoan that weakens monarchs and causes deformities such as crumpled wings, making them vulnerable to starvation and a quick death.
(Photo Credit: Nancy Lawson)


Nancy has observed both male and female monarchs scratching for PAs. It was thought that only male milkweed butterflies gather PAs, but females were gathering too, perhaps to pass the PAs to eggs. The first-stage larvae may get protection by eating their own PA-containing eggshells. 


Monarch egg

Monarch larvae eat their eggs, which could provide them with PAs for chemical defense. (photo: Amy Prentice)


What to Report to Monarch Rx

When citizen scientists report observing monarchs gathering PAs, there are a number of questions they are asked: What were the weather conditions? Did it just rain? What’s the condition of the plant? What plants are growing around it? How many monarchs are males and how many are females?

By better understanding what plants monarchs rely on, we can make better plant choices to benefit wildlife. It will be some time before studies can confirm the best plants for PA pharmacophagy for monarchs, but a lesson that we can put to use right now is that tidying up our gardens is not what’s best for insects. Beneficial insects — not just butterflies — use spent plants for food, habitat and (now we know) pharmacophagy.  


Monarch male scent glands

Male monarch butterflies have a pair of black spots on their wings. (photo: Brendan O’Reilly)


I hope you found my conversation with Nancy Lawson interesting and enlightening. If you haven’t listened yet, you can do so now by clicking the Play button on the green bar near the top of this post.

Do you see monarchs in your garden? Let us know in the comments below.

Links & Resources

Some product links in this guide are affiliate links. See full disclosure below.

Episode 012: Beneficial Garden Insects – Bringing Nature Home with Doug Tallamy

Episode 049: When Good Bugs Eat Bad Bugs: The Business of Beneficial Insects

Episode 050: Organic Pest Control: Beneficial Insects And Beyond

Episode 067: Predatory Beneficial Insects: Feared Foes of Garden Pests, Pt. 1

Episode 068: Top Predatory Beneficial Insects and How to Attract Them, Pt. 2

Episode 102: The Pollinating Power of Solitary Bees, and How to Attract These Gentle Insects To Your Backyard Garden

Episode 103: How to Create a Backyard Meadow: Simple Steps for Success No Matter the Space

Episode 147: Monarchs and Milkweed: A Precarious Struggle Between Life and Death

Episode 227: The Humane Gardener: How to Nurture a Backyard Habitat for Wildlife

joegardenerTV YouTube: How to Create a Wildlife Friendly Habitat in Your Garden or Landscape

joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.

joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!

joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.

joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.

joegardener Online Gardening Academy Growing Epic Tomatoes: Tomato expert Craig LeHoullier joins me in leading this course on how to grow healthier, productive tomato plants and how to overcome tomato-growing challenges. 

joegardenerTV YouTube

joegardener Newsletter

joegardener Facebook

joegardener Facebook Group

joegardener Instagram

joegardener Pinterest

joegardener Twitter

Growing a Greener World®     

GGW Episode 804: Gardening for Butterflies & Other Beneficial Insects 

GGW Episode 1011: Creating a Meadow Garden, Anywhere Around Your Yard

The Humane Gardener – Nancy’s blog

The Humane Gardener on Facebook

Nancy Lawson on Twitter

Nancy Lawson on Instagram

The Humane Gardener: Nurturing a Backyard Habitat for Wildlife” by Nancy Lawson

Citizen Science: The Monarch Rx Project

“Monarch Rx: Calling All Butterfly Watchers” on The Human Gardener

“Leaf-scratching — a specialized behaviour of danaine butterflies (Lepidoptera) for gathering secondary plant substances” by Michael Boppré 

The Kid Who Cares

Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution” by Anurag Agrawal

Rain Bird® – Our podcast episode sponsor and Brand Partner of

Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Exmark, Greenhouse Megastore, High Mowing Organic Seeds, Territorial Seed Company, Wild Alaskan Seafood Box and TerraThrive. These companies are either Brand Partners of and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.

About Joe Lamp'l

Joe Lamp’l is the creator and “joe” behind joe gardener®. His lifetime passion and devotion to all things horticulture has led him to a long-time career as one of the country’s most recognized and trusted personalities in organic gardening and sustainability. That is most evident in his role as host and creator of Emmy Award-winning Growing a Greener World®, a national green-living lifestyle series on PBS currently broadcasting in its tenth season. When he’s not working in his large, raised bed vegetable garden, he’s likely planting or digging something up, or spending time with his family on their organic farm just north of Atlanta, GA.

0 Responses to “230-Monarch Rx: The Prescription for Healthier Butterflies”

  • Garden Chick says:

    Quite a few in the garden and still some straggling through. I live in Kansas about 20 miles from Kansas City. I plant a lot of Monarch loving plants as I’m a Monarch Way Station through the University of Kansas. Loved this article and appreciate the info.

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