The Monarch versus
the herbicide
You don’t have to be a naturalist to appreciate the beauty
of the Monarch butterfly. In my thousands of hours in the outdoors each year, they never fail to capture my attention. It is one of those creatures, like
the Bald Eagle, that you simply never get tired of looking at. The fact that
they are reasonably common, even at our latitude, seems like a gift from the
creator, as well as a reason to dwell in meadows with blooming wildflowers on a
warm sunny day, when you are on a hike and still have miles to go. In recent
years, when I have been lugging a camera around, my knee-jerk reaction at each
encounter is to fish the camera out of my pack and capture the moment, even if
the light is terrible. Even a bad photo of a Monarch is worth saving.
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Monarch in Waterford, Vermont, in September. A migrant fueling up.
Oddly enough, this is in a power-line cut, demonstrating that Monarchs can capitalize on anthropogenic micro-habitats. |
I was a birder long before I paid much attention to
butterflies. When I did, I discovered that in size and color, the Monarch is
anomalous. It is a giant in a world with, say, thumbnail-sized blues (Polyommatinae).
All butterflies are vulnerable to predation, and you have to wonder how this
bug, with barely functioning camouflage, seems to avoid being eaten to death.
So the fact that it has an amazing story of migration is
consistent with its bold visual characters. Those outsized wings are engineered
for long-distance travel.
Unfortunately, we as a society now need to figure out
whether we will coexist with this amazing creature. Whether technology is
compatible with a magnificent pollinator molded by a million years of
evolutionary refinement. The US Fish and Wildlife Service (USFWS) has published
a proposed action to declare the butterfly threatened, under the Endangered
Species Act, and is seeking comments from us on how to proceed. Their
analysis is high quality.
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| A Monarch newly arrived in Danville, Vermont, in July. Nectaring on Common Milkweed (I think!) |
Monarch biology
Most of the Monarchs on the North American continent wait out the cold winter months in Mexico, in a state that approximates hibernation. (A smaller number winters on the California coast. A few more are residents in the southern US that don’t migrate far.) The warming days of spring wake them up and they head north. They fly until their fragile wings give out, then stop to lay eggs on (usually) a milkweed plant. Those butterflies progress through the stages egg-larva-pupa-adult, and then keep flying north. The adults will lay eggs and die. The cycle continues, four generations in total, so that they arrive in our yard in July, with some reaching Canada. Migration in butterflies is not uncommon: so far so good.
When the temperature and
the sun get lower in autumn, something astounding occurs: the adult butterflies turn around and head south.
Their parents did not do this; their grandparents did not do this. Some inner
urge causes this generation to behave radically different, and put those large
wings to work on a long journey. Butterflies born in the Gaspé
Peninsula of Quebec, Canada, having never flown more than a hundred meters, will
abruptly decide to fight headwinds and geographical barriers in an improbable
marathon journey of over four thousand kilometers to reach Mexico. And then the
second amazing thing happens. The butterflies don’t just find any warm spot in
Mexico for resting. They all end up in the same small region of Mexico,
in mountains west of Mexico City, where they congregate in Oyamel Fir trees
(known also, appropriately, as Sacred Firs!). Millions of them huddle together to coat tree branches. The wintering grounds, within the
Eje Volcánico Transversal, consist of only 20 hectares scattered across a region that is
only 60 km across, but they have flown for up to 4500 km to get there. These
bugs have no experience with these particular mountains; their parents have had
no experience. Somehow they know to keep beating their wings until ending up in
a favorable part of a mountain ridge in Mexico that stretches no more than the
distance from Boston to Worcester. (From Santa Fe to Abiquiu, if you are a New
Mexican.)
How the heck did this come to be? Long-distance migration,
in nature, is miraculous enough. But this is a bizarre multi-generational form
of long-distance migration. Behavior, in evolutionary theory, develops in a
step-wise fashion. What the heck were the steps that preceded a 4-generation,
sequential migratory leap across a continent, where one component is the
reverse of the others? If this were not a known phenomenon and some brave
scientist proposed it, he or she would get laughed out of the room. Utterly
absurd!
This kind of complexity in nature is the sort of the thing
that causes so much head-scratching that some people take refuge in
creationism. “It could not have evolved, so it must have been decreed by God,”
they say, the poor unimaginative souls. For those of us who accept the reality of nucleic
acids, however, it is still an amazing thing to ponder. An amazing component in
a tiny package of DNA that causes some individuals to fly north, other
individuals to fly south. Not randomly, however, but synchronously!
Bryan Pfeiffer has
written movingly of tagging a Monarch in Vermont, watching it lift off an
outstretched hand, and having it show up six months later in Mexico, 3700 km
away. I have never seen the Reserva de Biosfera de la Mariposa Monarca in Michoacán, but our scientist-musician friend Bette Korber was so
moved that she wrote a song about
the experience.
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| Monarch in Espanola, New Mexico. A September migrant. |
Let’s dispense
with creationist “theories” and contemplate how astonishingly complex is the
natural world. Monarchs can pull off the unlikely feat of migration because of complexity
in botany, which provides food for larvae and adults. It took millennia for
this partnership to emerge. Now it will take only a few decades for human
technology to undermine it. If we permit it to happen.
Biotechnology
It was about 60 years ago that a group of enterprising
chemists and biologists had an ambitious idea. A chemical could be used to
enhance the productivity of corn fields. It would suppress weeds but leave the crop unharmed. If farmers would buy it, more corn would grow and more people
could be fed. An undeniably attractive idea. Out of this came glyphosate.
The chemical had been known for a few decades, but Monsanto
had the idea to test its effect on growing plants. As industrial chemicals go,
it is quite simple: a combination of methylphosphonic acid and the amino acid
glycine, going by the formal name N-(Phosphonomethyl)glycine, C3H8NO5P.
(“Glyphosate” is a goofy tradename made up of pieces of chemical terms.) It
turned out to possess a few nice properties: it could be absorbed by a leaf; it
suppressed plant growth by interfering with an enzyme that produces amino
acids; and it degraded after action into relatively benign components (methyl
glycine, aminomethylphosphonic acid, both of which are degraded further by soil
microbes). It was much less aggressive than early herbicides like atrazine,
which produce persistent toxic byproducts in the soil. It was great at killing
competing native plants in crop fields (which farmers unceremoniously
designated “weeds”). Introduced in 1974, it gained favor in the late 1970s and
1980s. There was only one drawback: it harmed the corn, soybeans, and wheat,
making it tricky to apply.
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| Glyphosate (Roundup) and its degradation pathways in the environment. Taken from: JP Giesy et al., Ecotoxicological Risk Assessment for Roundup Herbicide, doi:10.1007/978-1-4612-1156-3_2 |
But gene editing technology was coming online in the 1990s.
Monsanto invested millions into finding an enzyme that was less hampered by
glyphosate, and they reprogrammed crop plants to produce it internally, thereby creating
modified crop plants that could be tolerant of the glyphosate. The combination
of weed-killing glyphosate and genetically-modified (GM) corn was a
biotechnology tour-de-force. Sales soared.
Glyphosate is now the most common herbicide in the world,
marketed under the trade name Roundup. The GM corn, known as “Roundup-ready
corn,” has utterly taken over the market. As have its cousins GM soybeans, GM
canola, GM alfalfa, GM sugar beets, and GM cotton. Mass production made the
Roundup affordable, and farmers were happy to purchase Roundup-ready seeds to
plant in the fields.
More people could be fed by an acre of farmland, using the powerful combination of GM crops and Roundup. It seemed like a giant step forward for humanity. One
issue apparently not considered seriously by Monsanto was the fact that
America’s cornfields were already quite productive, thanks to weed management practices
newly devised by agricultural research universities. (Which in turn are supported largely by our tax dollars.) This has become a common
oversight by the chemical companies. What problem are you trying to solve,
guys? And what new problems are you creating? Apparently these are regarded as
just philosophical questions.
Also missing from Monsanto’s research was examination of the
effects of removal of all weeds and native plants at the margins of cornfields.
Monsanto has great botanists, but their ecology department must have a bunch of
empty desks. One of the plants that suffered under the Roundup regime was
Common Milkweed, Asclepias syriaca. This plant grows in sunny openings
all over the northeast US. The Monarch evolved alongside it, using its flowers for nectar and its leaves
for growing caterpillars. Over the past million years, the plant and the butterfly
had become partners, with the plant facilitating the Monarch's long flight up to
Canada. The geographical ranges of the two species overlap beautifully in the
northeastern US – a classic case of co-evolution.
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Geographical range of Common Milkweed (top) and Monarch butterfly (bottom),
in the northeastern US and southeastern Canada. Illustrations taken from iNaturalist.org.
Each red dot is an observation documented at the site. |
A quick digression about nomenclature. I abhor the use of
the word “weed” in the name of a native plant. The vast majority of noxious
weeds with which we do battle in our yards, gardens, and roadsides are plants
introduced from other continents, which I have written about. Some native plants are slightly invasive, but that is not such a bad thing:
after all, these are the plants that restore land shortly after disturbance,
such as hurricanes, fires, and avalanches. So let’s resolve to adopt better
names for Asclepias syriaca and the many other examples. In fact, Common
Milkweed is named by some people “Butterfly flower.” A much nicer, more
enlightened, label.
“Butterfly flower” existed on this continent long before
humans, but when Europeans settled and mowed down northeastern forests, syriaca
gladly took advantage, and became more abundant in those sunny openings. Later,
when massive cornfields were established in the cut-over areas, syriaca became
common on the margins of these fields. To be sure, the native plant competed
with corn, at least a bit, by taking water and sunlight. This is the niche that
Monsanto seized upon with its glyphosate idea.
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| Monarch caterpillar in September. Feeding on a "Butterfly flower" that we planted in our yard. Once transformed into an adult, it will be on its way to Mexico. |
A. syriaca is the common Monarch plant in the northeastern
US, but there are others in the genus – about forty more. They march across the continent in partially overlapping ranges, but each is tuned to its own climate needs. All of them have fallen victim to Roundup spraying in crop fields. They are in
steep decline, and the Monarch is being dragged down with them. Twelve years
ago, researchers John Pleasants and Karen Oberhauser (at Iowa State and U. Wisconsin) examined milkweed species in the midwestern US and estimated a 58%
decline over a 12-year period in which Roundup use increased. The butterflies
can still use milkweed stands away from ag fields, but the midwestern US has
become dominated by crop fields, as any airline traveler can verify. Can we
save the Monarch through intensive planting of milkweed stands that are left to
prosper? Perhaps. If there is time. (And if we shun the planting of non-native milkweeds, which
likely harm the butterfly.)
Land, then, is not merely soil; it is a fountain of energy
flowing through a circuit of soils, plants, and animals.
– Aldo Leopold, The
Land Ethic
It's worth pausing to consider how we got into this
predicament. We once had healthy Monarch populations from coast to coast,
happily migrating from Mexico to southern Canada and back. They were so common,
so massively abundant that it was difficult to see how humans could pose any threat
at all. (This should trigger reminders of the Passenger Pigeon!) Technology in
our agricultural sector, however, has never stood still. Ag researchers are
talented and inventive. Farming never looks the same from one decade to the
next – this may not be obvious to big city dwellers, but those in the industry
are constantly implementing techniques and equipment that are newer and more
efficient. Nobody can argue that the impulse to do more is wrong. Feeding more
people with a given acreage of farmland is a good thing for the global
population. Monsanto has been the source of many new tools to help farmers be
more productive. There is at least one quantitative cost-benefit analysis
showing that Roundup pays off. (For European farmers, at least; I haven’t found a study for the northeastern
US.)
With Roundup, however, the early developers of the
technology looked only at part of the picture. Plants at the margins of crop
fields are there for a reason, if one is looking at the forces of nature. Our
planet became green and in places productive because plants and fungi are wired
to fill every niche in the ecosystem to its fullest. Evolutionary forces
ensured that plants, fungi, and butterflies seized every opportunity to expand,
into every corner in which the climate and soil were favorable. So when we
plowed the prairies and planted corn, and when we leveled the northeastern
forests and planted corn, the native plants jumped in to fill the gap. The
farmer spraying Roundup to kill those plants is much like some mythical
creature cutting off its toes to fit better into its footwear.
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| A migrant Monarch resting on a Rio Grande Cottonwood in Galisteo, New Mexico, in October. |
One basic weakness in a conservation system based wholly on
economic motives is that most members of the land community have no economic
value. – Aldo Leopold, A Sand County Almanac
One might ask: “Can’t an individual farmer take a stand, and
say ‘I’m not going to use chemicals?’” The answer is, “not really.” The
Metcalfe study posits Integrated Weed Management as a strategy alternative to
herbicides, but finds that crop yield would be significantly reduced. In Vermont,
Roundup spraying along with Roundup-ready crops have become the standard.
Farmers who can’t operate competitively will probably not survive for long. Of
course, organic produce and meat is an alternative approach (depicted sweetly in the film Biggest Little Farm), but realistically,
a large segment of Americans will always seek to economize with conventionally grown food.
The USFWS Proposal
After decades of analysis, lobbying, lawsuits, arguing, and
precious little action, the US Fish and Wildlife Service (USFWS) has released a
proposal to address this predicament. The proposal is to declare the Monarch butterfly
populations as Threatened. That label would apply to the populations migrating
to Mexico, but also those migrating to the California coasts, and even to the
small numbers in the southern US that don’t migrate at all. (In the past, the
population migrating to the Midwest was 85% of all Monarchs in North America.) The proposal
makes suggestions on saving the winter habitat in coastal California, too,
through a process known as Critical Habitat Designation. You should read this
proposal and then document your support of it, by the March deadline, at the designated website.
I’ve read my fair share of Federal Register Announcements.
They generally require a strong pot of coffee to make it through, and this one
is no exception. But the more I read, the more I like it. It encompasses an impressive amount of
peer-reviewed scientific literature. This Announcement
is clearly the result of years of work by a panel consisting of scientists,
administrators, and technical writers, the latter to improve readability. (Okay, I
have no idea if that last part is true. But having spent a career reading government
documents, I am guessing that it is, in this case.)
Everything seems to be aligned for the butterfly. A large
amount of science has been done. The general public is familiar with the
species. The Monarch is charismatic. The conclusion that the species is
Threatened seems inescapable. Possible mitigation actions, such as saving
forest in wintering areas and planting more milkweed, are easy to understand
and inarguable. What could go wrong?
The Trump Effect
To start with, we just had a national election. I fear that
the butterfly is going to become a casualty of the national discussion on
economic issues. I’ll have more to say about this in the future.
The politics of the Endangered Species Act are brutal. The
science can be compelling, the path forward clear, and still Congress can get
in the way. The Grizzly Bear, the Wolf, the Mexican Gray Wolf, the Lynx, the
Northern and Mexican Spotted Owls, the Sage Grouse, the California Gnatcatcher, the Black-capped Vireo, the Southwestern Willow
Flycatcher, the Black-tailed Prairie Dog, have all been penalized ostensibly in
the name of economic vitality. Thanks be to the Center for Biological Diversity for fighting these battles
without fatigue – they deserve your charitable contributions. But for those of
you who are new to ESA issues, be prepared for withering disappointments that
you never thought possible. Wildlife conservation legislation is almost always
used as a bargaining chip in deals on the floor of the Senate. The bitter truth
is that very few Congressmen place a high value on wildlife restoration. To add insult to injury, there are many cases where the species is Listed, but Congressmen take action to prevent any expenditure of funds on restoration.
The Trump administration has been here before. In 2020,
after an analysis that dragged on five years longer than mandated by law, Trump’s appointee at USFWS decreed that
Listing of the Monarch was “warranted, but precluded.” Do not mistake that for
anything less than dodging the issue. It’s a slick way to avoid blame for the
plight of the species, by whining that the money is needed elsewhere. The same
political forces in Washington that say “warranted but precluded” are the ones
who downsize the USFWS and make its job impossible even for the species with
approved recovery plans.
For the reasons I have outlined, a Listing of the Monarch
butterfly would call into question the current practice of spraying of Roundup,
which is the basis of an industry worth many billions. That will not go unnoticed by conservatives, who will lean on the political
appointees at the Department of Interior, who will go out of the way to please
their boss at the White House. A battle is brewing between conservation groups
and the agricultural industry.
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| Monarch in September. Caledonia County, Vermont |
Could the conflict be defused? Yes. Spraying practices for
Roundup could be changed. (Friends in our neighborhood lost their vegetable
garden to a drifting cloud of glyphosate.) The spraying equipment could be
upgraded to hit only the rows of crops planted, and to leave the margins clean.
Larger aerosol particles would stay put better. That could be achieved with a
little more technological innovation by John Deere, and then by requiring that
farmers adhere to the new methods. Spraying could be restricted to windless
conditions. A win-win story is within our grasp, but only if new rules and new
spraying technology are implemented well and in the least disruptive way. As a
country we have a terrible track record at implementation. Excessive
bureaucracy and flawed rule-making almost always cause disruption, which makes
industry people unwilling to accommodate changes.
This is an important aspect of regulatory reform for which,
in my view, conservation groups need to become more aware and more pragmatic.
It’s of little use to ask the US Government to parachute in on an industry and
say “starting today, you will need to change everything in the way you conduct
business.” We live in a capitalist system, and we favor entrepreneurs who make
things better, and this applies as much to crop spraying as it does to
pharmaceuticals that cure disease. Every day, you and I support the
agricultural industry when we go to the grocery store. We are all part of the
system.
For the long term, Monsanto could go back to the drawing
board. They could find a replacement for a “weed killer” that has less impact
on the genus Asclepias of milkweed plants. Now there’s a niche for some good
old American innovation! To some extent, the need for a new herbicide is
already getting more urgent from observations of weeds that have resistance to Roundup.
Here’s some more bad news: herbicides are not the only
threat to the Monarch. There is one recent scientific paper that maintains that insecticides are an even greater threat. This illustrates a
fundamental characteristic of threatened species: there are
multiple factors to blame. Restoring species will always require a range
of actions.
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Queen butterfly, near Melrose, New Mexico. A mimic of the Monarch,
thought to have evolved a similar pattern to deter predators |
All in all, I am trying to remain optimistic about the butterfly. If the USFWS receives an avalanche of comments supporting listing of the butterfly, the Trump administration might want to avoid the embarrassment of a rejection. Even more likely, though, we can all sit tight for four years and hope that the next enlightened administration will measure public support and act accordingly. So get your comments in!
In the meantime, the forests in Mexico need protection. The film The Guardian of the Monarchs portrays Mexico’s brave butterfly defenders as being hopelessly outgunned by gangs engaged in illegal logging. One of the groups trying to defend the Monarch preserve is World Wildlife Foundation (WWF), to whom you can contribute here. Let us pray that WWF can help defend the Oyamel Fir forests until Trump is out of office, when some real protective measures in the US breeding habitat can be emplaced. We have been WWF contributors for years, and we’ve seen the results of their work in many countries. Sadly, though, an effort many times larger than the current one in Mexico will be needed to be effective.
If all efforts fail and we lose the Monarch butterfly, we
will surely lose many other species that also depend on milkweeds in some way.
We just don’t know about those species yet. Just as we didn’t know about the
Monarch’s winter forests until 1975. As we didn’t know about the breeding needs
of the Marbled Murrelet, until an accidental discovery in old-growth forests in
the 1970s. What we don’t know about the wildlife in our own backyards far
exceeds what we do know.
We abuse land because we regard it as a commodity belonging
to us. When we see land as a community to which we belong, we may begin to use
it with love and respect. There is no other way for land to survive the impact
of mechanized man, nor for us to reap from it the esthetic harvest it is
capable, under science, of contributing to culture. That land is a community is
the basic concept of ecology, but that land is to be loved and respected is an
extension of ethics. – Aldo Leopold, Forward to A Sand County Almanac
Where to learn more
There is an enormous amount of information available on the
internet. From a technical standpoint, the quality varies. Here are some
sources I’ve looked at and recommend for further insight.
Reppert, Steven M., and Jacobus C. de Roode.
"Demystifying monarch butterfly migration." Current Biology
28, no. 17 (2018): R1009-R1022. https://doi.org/10.1016/j.cub.2018.02.067
Metcalfe, H., Storkey, J., Hull, R. et al. Trade-offs
constrain the success of glyphosate-free farming. Sci Rep 14,
8001 (2024). https://doi.org/10.1038/s41598-024-58183-8
Wayne E Thogmartin et al 2017. “Restoring monarch
butterfly habitat in the Midwestern US: 'all hands on deck.’” Environ. Res.
Lett. 12 074005. https://dx.doi.org/10.1088/1748-9326/aa7637
Pleasants, J., Thogmartin, W.E., Oberhauser, K.S., Taylor,
O.R. & Stenoien, C. (2024) A comparison of summer, fall and winter
estimates of monarch population size before and after milkweed eradication from
crop fields in North America. Insect Conservation and Diversity, 17(1),
51–64. https://doi.org/10.1111/icad.12687
John M. Pleasants, Ernest H. Williams, Lincoln P. Brower,
Karen S. Oberhauser, Orley R. Taylor, Conclusion of No Decline in Summer
Monarch Population Not Supported, Annals of the Entomological Society of
America, Volume 109, Issue 2, March 2016, Pages 169–171, https://doi.org/10.1093/aesa/sav115
A useful USFWS page: https://www.fws.gov/initiative/pollinators/save-monarch
The Monarch Joint Venture: https://monarchjointventure.org/
The Xerces Society on what you can personally do for the Western Monarch: https://xerces.org/western-monarch-call-to-action
The Xerces Society on what plants are needed to sustain Monarchs in your region: https://xerces.org/monarchs/monarch-nectar-plant-guides
The Center for Biological Diversity has been the force behind legal action to save the Monarch: https://www.biologicaldiversity.org/species/invertebrates/monarch_butterfly/
And then the incomparable David Attenborough: Planet Earth III (2023)
