01 Apr 2013

Tracking the Causes of Sharp Decline of the Monarch Butterfly

A new census found this winter’s population of North American monarch butterflies in Mexico was at the lowest level ever measured. Insect ecologist Orley Taylor talks to Yale Environment 360 about how the planting of genetically modified crops and the resulting use of herbicides has contributed to the monarchs’ decline.
By richard conniff

University of Kansas insect ecologist Orley R. “Chip” Taylor has been observing the fragile populations of monarch butterflies for decades, but he says he has never been more concerned about their future.

Monarchs are beloved for their spectacular migration across Canada and the United States to overwintering sites in central Mexico — and back again. But a new census taken at the monarchs’ wintering grounds found their population had declined 59 percent over the previous year and was at the lowest level ever measured.

Orley Chip Taylor
Monarch Watch/Catherine I Sherman
Orley Taylor
In an interview with Yale Environment 360 contributor Richard Conniff, Taylor — founder and director of Monarch Watch, a conservation and outreach program — talked about the factors that have led to the sharp drop in the monarch population. Among them, Taylor said, is the increased planting of genetically modified corn in the U.S. Midwest, which has led to greater use of herbicides, which in turn kills the milkweed that is a prime food source for the butterflies.

“What we’re seeing here in the United States,” he said, “is a very precipitous decline of monarchs that’s coincident with the adoption of Roundup-ready corn and soybeans.”

Yale Environment 360: The study that happened in December indicates a pretty dramatic decline in the monarch population. Could you describe what that study found?

Orley Taylor: The measure of the overwintering colonies takes place every December down in Mexico, and what that measures is the total area of trees that are occupied by monarchs in up to twelve different overwintering sites. They’ll have a team that will go up into the forest and they will examine all of the trees that have got butterflies on them. The butterflies tend to be grouped, so there might be 47 trees in one area covered by butterflies, and there might be another area which has 427 trees covered with butterflies. They measure the polygons occupied by these fir trees, figure out the area of each one, and add them all together.

It came out to only 1.19 hectares this year, about 2.74 acres, the smallest all-time measure. In 1996, we had an overwintering population that was almost 18 times larger.

e360: What percentage decline did the current study find, over one year?

Taylor: It was a 59 percent decline, but that’s not really important. In 2003-4, the population declined a lot more from one year to the next. So it’s not the total percent decline. It’s the total amount of butterflies that are out there that we’re really concerned about.

e360: In the past they bounced back, and you think the prospects are less likely for that now?

View gallery
Monarch Butterflies

Jim Lovett/Monarch Watch
A cluster of monarch butterflies in Mexico.
Taylor: One of the things that you can say about almost all populations is that when they get really small they get very vulnerable to one perturbation or another. What we’re really worried about here is that there would be some sort of catastrophic event that can send the population spinning downward even more. Then the impetus for conservation of the population could weaken — because if you don’t see them, you don’t have the motivation to do something about it.

e360: A lot of Americans assume the problem is deforestation of the monarch’s winter habitat in Mexico. How has that situation changed?

Taylor: They’ve made a terrific effort to control illegal logging down there [in Mexico], and the last report they had showed that they had completely eliminated illegal logging by the organized mafia-like groups that go in there with guns and cut down a hectare of forest in one night with 15 or 20 trucks and then haul it all off before morning.

e360: That’s stopped?

Taylor: As far as we know, it’s stopped. But there still is a little nibbling at the forest here and there, and that’s very hard to control. You’ve got a lot of people living close to the bone, and each of those mature trees is worth about $300. It’s a fairly big area, it’s remote, and the question is, how do you patrol this area? How do you eliminate the day-to-day things that are going on in remote mountainsides?

e360: Let’s talk about the problem on the American and Canadian end of the migration.

Taylor: What we’re seeing here in the United States is a very precipitous decline of monarchs that’s coincident with the adoption of Roundup-ready corn and soybeans. The first ones were introduced in 1997, soybeans first, then corn. By 2003, 2004, the adoption rate was approaching 50 percent,
The use of Roundup ‘has effectively eliminated milkweed from almost all of the habitat monarchs used to use.’
and then we really began to see a decline in monarchs. And the reason is that the most productive habitat for monarch butterflies in the Midwest, in the Corn Belt, was the corn and soybean fields [where milkweed, which monarchs feed on, grew]. Before Roundup-ready crops, weed control was accomplished by running a tiller through those fields and chopping up the weeds and turning over the soil, but not affecting the crops. The milkweed survives that sort of tillage to some extent. So there were maybe 20, 30, 40 plants per acre out there, enough so that you could see them, you could photograph them.

Now you are really hard pressed to find any corn or soybeans that have milkweed in the fields. I haven’t seen any for years now because of the use of Roundup after they planted these crops. They have effectively eliminated milkweed from almost all of the habitat that monarchs used to use.

e360: The amount of herbicide sprayed on these fields has gone up?

Taylor: Oh, yes, it’s gone up. The glyphosate used in agriculture has tripled since 1997, when they first introduced these Roundup-ready crops. The developers of these crops not only provided the seeds that were glyphosate-resistant, but they also provided the glyphosate — the Roundup. And, boy, that was a pretty good system. You could make money on both, right?

e360: Right.

Taylor: For the farmers it looked good too. If I was a farmer and I was holding two jobs to keep my farm and I didn’t want to have my rear end sitting on the tractor too long, I would use that product as well, because the ordinary mechanical tillage took a lot more time and cost a lot more money.

View gallery
Monarch Butterflies

Jim Lovett/Monarch Watch
Hundreds of monarchs fill the sky at their wintering ground in Mexico.
e360: This is not the sort of thing people originally worried about with genetic engineering — it’s not a mutant gene getting loose, it’s not food safety. It’s just a change in conventional farming practice.

Taylor: It’s a collateral damage issue. And one of the things that we’re worried about now is that it looks like there’s going to be a lot of collateral damage from the use of various herbicides and pesticides coming down.

e360: You’re worried about other genetically-engineered crops?

Taylor: Yeah, there’s apparently 15 genetically-engineered crops in the pipeline. One of the concerns is that some of them are stacked. That is to say, they’re genetically engineered to resist not just one herbicide, but two, three, four different classes of herbicide. Some of those herbicides are noteworthy for having a lot of collateral damage already because they are volatile. They tend to be difficult to confine, and so they are likely to be dispersed when they are applied and affect areas outside of the field. And that could have a tremendous impact on the vegetation, on the pollinators and, of course, on the monarch butterflies.

e360: There’s more going on here, though, than genetically-engineered crops?

Taylor: Ethanol is a big issue too. We’ve seen a 25.5 million-acre increase in the amount of corn and soybeans since 2006. And that’s been at the expense of nearly ten million acres of Conservation Reserve Program land, which farmers are paid to set aside for wildlife. The other 15.5 million acres means that farmers had to plant a lot of marginal land — that would be milkweed habitat, pollinator habitat, rangeland, grassland and so on. So there has been a tremendous change in agriculture to accommodate the
We can have an impact if we get the gardeners in this country to help us out by planting milkweed.’
production of biofuel. The price of corn and the price of soybeans has gone way up. There is also an increase in international markets.

So a combination of things have pushed the corn and soybean acreage up to the highest level since just after the Second World War — 169 million acres of corn and soybeans were planted last year. This is just an unprecedented amount of landscape put into those particular row crops. What farmers are tending to do — and you can’t blame them — is that they are narrowing field margins. They are getting closer and closer to the edge of the road. These strips from the road to the field are often six or eight feet wide, and there’s nothing in there but grass.

e360: And in the past it would have been milkweed?

Taylor: You’re basically creating a desert out there, except for the corn and the soybeans.

e360: It’s ironic that the Conservation Reserve Program (CRP) is suffering because of another government program [for ethanol] that was ostensibly intended to protect the environment.

Taylor: Yes, exactly. We have 27 million acres of CRP land right now, and that’s going to go down to about 24 million acres. Congress has actually dictated that the CRP land should be capped at about 25 million acres. Well, it’s going to go below that because of these other economic forces.

e360: So are there prospects for monarch recovery given all these things weighing against it?

Taylor: Basically for monarch recovery we’re going to have to create a lot of milkweed habitat. And the question is where are we going to do it and how are we going to mobilize people to do it. What people are going to be asked to do is to save wildlife by creating habitats in their gardens.

e360: But gardens are not going to make up for 25.5 million acres of additional corn and soybeans.

Taylor: No. It’s an Alice in Wonderland story of the Red Queen’s race. You have to run as fast as you possibly can to stay in one place, and if you want to get any place, you have to run twice as fast. But I have to believe that we can have an impact if we get the gardeners in this country to help us out by planting milkweed and putting in native plants to stabilize native pollinator communities. So people now have another purpose for creating a garden. The purpose is conservation.

e360: This is the best-known butterfly in America and it’s also the state insect in six or seven states. But it sounds as though it might be on the path to extinction.

Taylor: I wouldn’t say extinction. Monarchs could disappear from the vision of most of us in this country as the migration goes way, way down. But the butterfly will persist. On the other hand, if we start talking about climate change, then we may be looking at an even grimmer scenario.

e360: I saw a recent study projecting a 73-100 percent decline in suitable conditions at those overwintering sites.

Taylor: A study by some Mexican colleagues is projecting that by 2030 the temperature will be so high at those overwintering sites that a lot of the
Monarchs could disappear from the vision of most of us in this country as the migration goes way down.’
trees will begin to die and the microclimate that butterflies need is going to become vanishingly small. I hate to think that they’re correct. Their projection is based on the temperatures in those mountains increasing by two degrees centigrade in that 17-year period. And if the planet has temperature rises that are that fast, we’re not going to be talking about monarch butterflies. We’re going to be talking about survival of a lot of things.

e360: You teach a course about the world in 2040, when your current students will be in their 50s. What does the fate of the monarch say to you about how that world is going to look?

Taylor: You know, I don’t even put the monarch in that world. I mean you know the population is projected to increase by two billion people by 2040. Well, we can’t do that. We are going to see a lot of changes, a lot of restrictions on how fast populations can grow simply on the basis of our food production, the declining available arable land, the limitations on water. If we don’t get with it and if we don’t start modifying our behavior, then things are going to get really out of whack.

But you know there’s still a chance and there’s still a way that we can deal with things fairly effectively. I mean almost every day there are new things that human beings have come up with which will help us deal with some of these crises ahead. We are going to have to make a lot of adjustments. And if we don’t make these adjustments, life is going to get to be pretty tough.

e360: So in all of this, the decline of the monarch butterflies is a kind of side show.

Taylor: It is. It’s my way of introducing people to the larger issues.


Richard Conniff, who conducted this interview for Yale Environment 360, is a National Magazine Award-winning writer whose articles have appeared in Time, Smithsonian, The Atlantic, National Geographic, and other publications. He is the author of several books, including The Species Seekers: Heroes, Fools, and the Mad Pursuit of Life on Earth. In previous articles for Yale Environment 360, he has written about the pricing of ecosystem services and about new advances that could help produce food crops that can thrive as the climate shifts.

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I tried to plant a 4,000-square-foot Monarch garden last year and because of the intense heat and drought almost nothing came up. I spent several hundred dollars, I watered religiously and it was an utter failure. I don't think I will attempt it again. If I can find a way to do just the milkweed I may try it, but not this year. The economics are against it. I have almost 100 trees and shrubs in my private park that I have to keep alive for songbirds, and I lost some last year at that. It's harsh to pick and choose priorities for wildlife. I hate it. I can only try to do the best based on what is already alive and what I can save now.

Posted by Kathleen M Isabell on 01 Apr 2013

I maintain three very large milkweed gardens, but after 2006 have been lucky to have one monarch, come by each season. I know i will probably see none this year. So very sad we, humans are destroying the Earth God gave us to enjoy. A Monarch butterfly is a wondrous creature only God could have made, I miss them.

Posted by DOROTHY HIXSON on 02 Apr 2013

Something I have found to be very helpful here in hot, dry South Central Texas is to plant some of the higher water need plants (milkweed seems to be one) is to give them a lowered bed (as opposed to a raised bed) preferably in the shade and use some clayey soil ( as opposed to sandy). Provide some supp water when it gets really dry, the dug out bed and poor draining soil should retain water / moisture for the Milkweed and an additional benefit is puddling for all butterfly sure to let natives come up.

Posted by Kay Mile on 02 Apr 2013

This is really shocking. I knew of some of the earlier habitat issues, I was not aware of the impact agribusiness was having on the monarch population. I really appreciated the information.

Posted by Charlie@Seattle Trekker on 04 Apr 2013

Population is a red herring. So too are "gardeners".

Many many other species are casualties of our farming systems and we should be trying to save them all and not focussing on specific remedies for individual butterfly species. Planting milkweeds, if it worked, just hides the problem and makes us forget the big picture.

Posted by Jonathan Latham on 05 Apr 2013

This is horrible, I grow milkweed in my vegetable garden. Had three butterflies born this week. I see we are in trouble folks, killing the butterflies and Bees will come back to haunt us. In Florida it is illegal to move bee hives, they want them destroyed.

Posted by Beverly the veggielady on 06 Apr 2013

Orley, Thank you for your study. Be sure the president of Mexico is going to do the poible to add a solution in the Mexican part.




Posted by MARIA VALLEJO on 06 Apr 2013

Those in droughty areas might try butterfly milkweed (Asclepias tuberosa) instead of common milkweed. It's a low growing species with beautiful orange flowers. Monarchs will use it as a host plant and it grows over much of the country, except the Northwest. Go to for subspecies for your area.

Posted by Cliff Fairweather on 07 Apr 2013

I did a survey of monarch butterflies in Toronto (2010), specifically looking at brownfields and how they benefit the species. I have found that there are far more monarchs on brownfield sites than in urban parks. The main reason for this is the absence of regular management (pruning, weeding, pesticides etc.) on brownfields, thus there is a larger number of milkweed on those sites. Unfortunately, the majority of those sites have disappeared and gave way to the storage of construction machinery, cars or parking lots, and now consist of compacted or paved ground.

Posted by Thierry Spiess on 09 Apr 2013

I'm from one of the communities near the Monarch Butterly Santuaries... Im so upset of how things are turning out... There is so much I want to do!! The community that lives in the Santuary sorroundings need to be made aware of what will happen if we don't take care of this miracle.. I often go visit my grandparents and every time I go, it makes me feel so sad...the community is so blinded...I want to help but do not know what to do..I need counseling.. my email is


Posted by Xavier Cruz on 11 Apr 2013

Thank you for resolving this mystery and danger to the Monarch population. Now I suppose someone needs to have a talk with the local farmers and get them to go back to tilling the milkweed unfer again. It would seem a simple solution.

Posted by Jessee McBroom on 18 Apr 2013

Thank you for your article, I also enjoy the Monarch and am greatly be saddened by their decline. But your article unfortunately makes assertions that may be related but are not the root cause. Farmers are driven by market factors in their choice of crops and herbicides. The increase in Corn and Soybean prices is the single biggest driver in the increase in Corn/Soybean production. CRP (if funded) may or may not be as profitable to a farmer. Use of herbicides and farming to the edge was also done before the new kind of seeds, the wide fence row has been gone for decades! My solutions: The Ethanol program should be reduced or eliminated to allow market forces to dictate ethanol use. The CRP programs should be made more robust and/or expanded.

You also should not ignore the impact of the 13 year long drought that has ravaged the southwest and at times up into the Midwest and Rockies. This has greatly reduced all weeds and flowers in the wild. The CRP, even if not planted, would carry little if any milkweed. Till this drought ends, we will see all species decline.

Posted by Lee on 24 Apr 2013

I did not know much about Monarchs until five months ago, bought a plant not knowing it is milkweed. Three weeks ago I saw a Monarch was laying eggs on that plant. I have about 26 caterpillars, four pupated. I educated myself and family more about Monarchs and how can we help even if we have a little patio!

Posted by Meena on 26 Apr 2013

I planted wild milkweed in my vegetable garden 2 or 3 yrs ago, just for the Monarchs, and I also planted the beautiful orange BUTTERFLY WEED? I saw only a few Monarchs last year....and not a single one this year, at all. I live in the Upper Midwest, not far from Canada's border. I am just sick over this. Where I am originally from, N.W. Florida near the coast, we used to see HUGE numbers of the Monarchs come there on their migration. I am just sick over this.

Posted by cynthia on 21 Jul 2013

The only thing surprising about linking the massive fields of corn grown for ethanol is that someone in the environmental studies field finally made the connection.

Posted by Diann Mabus on 07 Aug 2013

The monarch is much like the canary that was taken into the indicator of the health of the environment. Serious thought and action must be given as to how we are going to protect our fellow creatures in the world. If we protect them, we also protect ourselves.

Posted by Jackie Rosales on 07 Aug 2013

I live in Central Texas where we are experiencing drought conditions. My friend up the street found five monarch cats on her milkweed this past week - we are sharing in raising them. But it is a strange time of year for Monarchs to even be here!

We are hoping all ours will be healthy and that they will grace us with another generation.

I keep some of my milkweeds in pots and keep them inside during the winter months so they are ready to go in the early spring.

Last year the monarchs showed up early and I was glad I had the plants and managed to release about 14 healthy specimens.

Posted by Anne Worner on 08 Aug 2013

We live on the shoreline of Lake Huron in western Ontario. For several years we were thrilled to see thousands of monarchs congregating in the trees near our house before their fall migration. This year we have seen only one or two all summer, in spite of open, uncut hay fields behind our house and a good crop of milkweed.

Our local apiary has lost over 60 percent of its bees, mostly to an insecticide used on grain seed. No doubt this seed treatment is part of the problem with the monarch population too. We need these pollinators to help maintain our native and domestic plant populations.

Maybe the cost of a few weeds is worth it if we can help maintain nature's balance. After all, if these chemicals are having such a broad effect on our insect populations, what are they doing to us as we consume food grown using them?
Posted by Richard Emmerton on 25 Aug 2013

Every year my daughter and I catch caterpillars from our large field and hatch them in summer school. Last year was like any other, with a large number of cocoons, but a terrible infestation took place! About 80 percent turned black and died while cocooned. We actually were able to watch a small worm make a hole from the inside out and dangle from a nasty slime string until it dropped onto the bottom of the cage. It then hardened up and the hatched out as a fly. I do have photos. It was horrifying to see! An introduced bug? And then this year we have not found a single caterpillar!
Posted by Jessica Lewis on 26 Aug 2013

I made a comment earlier and did not state where the issue was from. I am from Antigo, Wisconsin.
Posted by Jessica lewis on 26 Aug 2013

I live i Mount Zion, IL, and I am attempting to gather milkweed seed/pods and save the seed to either send to Monarch Watch in KS to grow and disperse, or to save for my local area and try and find someone in the area to grow the seed to sell. They have to cover their costs and make a profit too.

Have you tried this in your area? What success and/or problems have you had? Things for me to give priority to and/or stay away from? Other ideas? I have not tried to make the milkweed seed separator yet, but I will, or get help to make it.

I would like to ask the 4-H to help, as many live in the country and have family and friends who have land on which milkweed grows and or could grow.

It will take many volunteers, land, money, cooperation from the farmers/land owners not to spray an area set aside for the milkweed and other flowering weeds, milkweed seeds collected and saved and sold and planted and God's help to provide favorable conditions, and the cooperation of the the monarch butterfly and the Mexican or Florida or California governments at the wintering-over sites for this to succeed.

We need to start now to collect the milkweed seed so that it can be planted this fall or in the spring next year.

Thank you. God Bless!
J C Nashland
Posted by J C Nashland on 27 Sep 2013

I used to work for a county cooperative extension. I created a simple, educational presentation on the monarch butterfly that I gave to many groups around the county. I included a pledge form for people to sign, promising that they would plant milkweed on their property. I also shared milkweed pods and gave out seeds for them to take home and plant. How can I keep this project going?
Posted by Shane VanOosterhout on 14 Oct 2013

I live along the shore of Lake Michigan. This was the first year I noticed the drastic decline in monarchs. Hard to imagine a day when there are few or no monarch butterflies left. Thank you for educating us on the probable causes and ways to help. We do have milkweed growing wild and spreading on our property. I will now take as much pleasure in maintaining it as I do in maintaining our vegetable garden.
Posted by Tom Pushaw on 14 Oct 2013

Not much good news about the situation since the April interview. How about another update?

Posted by Gaylord Inman on 25 Oct 2013

I love monarch butterflies and they are almost all gone. We have to do something about this — we can't just sit here and see them go extinct. Let's get up and fight against GMOs.
Posted by juliana on 10 Feb 2014

Do what you can, plant milkweed. Free milkweed seed available in Canada"
Posted by ivan Mcilroy on 15 Feb 2014

Chip Taylor mentioned that we projected a temperature increase of about "two degrees centigrade in that 17-year period." That is not exact. We estimated an increase of 1.5 degrees C for the decade centered in year 2030 in comparison with the average temperature for the 1961-1990 period, and not in comparison to 2012 or so. Because at present it has inccurred a warming of approximately 0.8 or 1.0 degrees C, we can expect that from today (2014) to 2030, it will experience an increase of approximately 0.5 or 0.7 degrees C, which is quite realistic. In any case, Chip Taylor is absolutely right when it says that "if the planet has temperature rises that are that fast, we’re not going to be talking about monarch butterflies. We’re going to be talking about survival of a lot of things." Yes, by the end of the century, the ecological disaster will be beyond imagination. See our paper in:
Posted by Cuauhtemoc Saenz-Romero (Morelia, Michoacan, Mexico) on 27 Feb 2014

I don't agree that the herbicides are doing much if any damage, at least in California (where they use plenty of them). But I guess that's where the big money grants are. The problem is that all the fields of milkweed have been developed into housing tracts, landscaped parks, and row crops (herbicides aren't the problem with row crops, the row crops are the "problem"). I've been "growing" monarchs for years — it's 3/11/2014 and I have more than I can handle right now. Another problem I now have is Argentine ants which attack the chrysalises created "outside." Native ants didn't seem to bother the chrysalises. So we made a monarch hotel where we gather the caterpillars and put them up on tables in screened in enclosures with potted milkweeds. It's a shame if the causes of the decline is misinterpreted as being due to herbicides if that isn't the case, and I'm confident it's not the case where I live — and probably nowhere else.
Posted by Randy on 11 Mar 2014

Efficient large-scale farming is not going to go away. It can't go away if we are to feed an ever-growing world population. A more solutions-based dialog is needed for readers. What smart goals should environmentalists set to combat big ag food deserts? Should there be a push to expand the Conservation Reserve Program (CRP)? Do you think the general public can make an impact through programs like Project Milkweed ( Setting clear, reachable goals makes things happen. Postulating and pointing fingers leads to more postulating and finger-pointing.
Posted by Jessie on 26 Mar 2014

In September 2013, while traveling north on Michigan's I-75 highway, I noticed that many Monarch butterflies were using the highway corridor as a migration route. I was killing them against my grill and windshield, as were all the other vehicles. Vehicle-butterfly mortality may be a factor in the decline.
Posted by Rico Torreano on 04 Apr 2014

I have a small milkweed garden, but recently released 36 monarchs over the course of a 2-week period. I know I am only one person but I think that if each of us does our own little part we can help the monarch population.
Posted by erin on 27 Jun 2014



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