The Monarch Abundance Roller-Coaster- part 2


Guest Post By Jim Steele

To be published in the Pacifica Tribune February 2020

What’s Natural

Indeed, some Monarch populations have declined in recent decades. However, the species as a whole is not endangered. Monarchs experience booms and busts as do many insects. So, we still need to determine if recent population declines are part of natural cycles or due to human disturbance. Counter-intuitively, humans purposefully and unwittingly have both increased and decreased monarch populations.

Eighteen thousand years ago, most of the breeding habitat for North America’s eastern monarch populations was covered in ice sheets and permafrost. Unfortunately the monarchs main food plants, Common Milkweed and Showy Milkweed, are frost intolerant. Today those milkweeds die back each autumn, forcing monarchs to migrate south. Habitat south of the ice sheet was covered with dense forests, which also limited the milkweed species that require warm open habitat, and disturbed ground. As the earth warmed and ice retreated, milkweed migrated northward colonizing glacially disturbed landscapes. Likewise, monarch populations expanded.

However, some scientists suggest the monarch’s awe-inspiring abundance really boomed during the past 200 years after European colonists began extensively logging America’s dense southern and eastern forests. Logging created more open fields and pastures, more farms and roadways; habitat milkweeds still favor today. More milkweeds, more monarchs.

In addition, gardeners adored showy milkweed flowers, so began planting milkweed across the globe. Again, the monarchs followed. Suddenly monarchs expanded out of North America and across the globe. Around 1850 monarchs reached Hawaii likely as stowaways on trading ships, then spread to several Pacific Islands. With optimally warm climates monarch populations boomed, feeding on introduced milkweeds and closely related native species. But monarchs often decimated their food plants causing island monarch populations to bust.


By the turn of the century monarchs were found in Australia, New Zealand, Indonesia, the Philippines and southeast Asia. They also spread across the Atlantic to the Azores, Canary Islands, Spain, Portugal and Morocco. In many regions, monarch populations are now stable. Where warm temperatures permitted milkweeds to grow all year, monarchs no longer migrated. Having successfully colonized much of the suitable regions of the world, insect experts don’t fear monarch extinction. However, concern remains for the USA’s eastern population that winters in Mexico.

The wintering population in Mexico was first surveyed in 1993. By 1997, the population boomed, tripling its abundance. But then winter populations worrisomely declined. Paradoxically, surveys of monarchs in their midwestern breeding habitats found no evidence of declining populations. But such surveys were done in “natural” habitat, not agricultural fields. It now appears the rise and fall of milkweed in agricultural fields drove the booms and busts of 20th century monarchs.

Having successfully colonized roadway ditches and any open disturbed landscapes, milkweed species began invading the open fertilized ground between rows of crops. Monarch populations boomed, while the farmers’ crops suffered. Studies estimated milkweed competition reduced harvests of wheat and sorghum by 20% and most states declared milkweed a noxious plant. But when farmers tried to eradicate milkweed by mowing, they only stimulated its underground roots promoting a greater infestation. Likewise, for herbicides that only eliminated stems and leaves. Tilling the fields only fragmented milkweed roots, again causing milkweed to multiply. The growing battle to eliminate milkweed started the monarch’s mid 20th century decline. With the 1970s discovery that the herbicide glyphosate killed the whole plant, the loss of milkweeds in the monarch’s human-made breeding grounds accelerated.

Still, there was room for optimism. Monarchs continue to breed throughout their traditional habitats. More efficient agriculture allowed more land to revert to “natural” states. Furthermore, the federal Conservation Reserve Program (CRP) was successfully compensating farmers to take environmentally sensitive land out of crop production. The good news was the majority of Midwest monarch breeding habitat was found on lands enrolled in the CRP. But fossil fuel fears reversed all that promise. The 2005 Energy Policy Act and the 2007 Energy Independence and Security Act instituted subsidies and quotas that rewarded biofuel production.

As a result, U.S. corn harvests for ethanol rose from 6% in 2000 to 43% percent in 2012. The monarch’s remaining “natural” breeding habitat was increasingly eroded as corn acreage increased by 17 million acres since 2006. Lured by lucrative biofuel subsidies, farmers increasingly abandoned the CRP program. Soon thirty percent of the CRP’s sensitive lands converted back to growing corn and soybeans for biofuels.

Perhaps the loss of milkweed in agricultural lands, will only reduce monarch populations to their “natural’ levels of the 19th century, before modern agriculture opened the land for more milkweeds. Monarchs may become less common, but not endangered. For monarch lovers, our best safeguard is to halt the spread of biofuels and plant more milkweed in our gardens.

Jim Steele is Director emeritus of San Francisco State University’s Sierra Nevada Field Campus and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism

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Fred Harwood
February 8, 2020 10:29 am

Here in southwest Massachusetts last summer, we experienced the most monarchs of our 70+ years. Especially in morning, we needed to drive carefully along dirt lanes to avoid them as they puddled for minerals.

February 8, 2020 11:24 am

Jim==> Are the official 2019-2020 Mexico monarch numbers in yet?

Kurt Linton
February 8, 2020 11:54 am

“So, we still need to determine if recent population declines are part of natural cycles or…” Why?

Reply to  Kurt Linton
February 9, 2020 6:54 am

Agreed. Besides, I thought humans WERE part of the natural cycle (again, unless we are aliens or special creations by God).

What we really are determining is “Do we want more monarchs?”. Saving species is about whether or not we like them. Polar bears are cuddly (never mind they eat people), so are wolves (yeah), koalas, butterflies, and so forth. You saw people saving koala bears in Australia, but no one ran in to save any endangered spiders. Most likely, they cheered the prospect of the demise of the species. Conservation has always been about saving what most humans like (see panda bears for a prime example), up until AGW and the arrival of the money lottery for “renewables”. Greed outranks conservation and cute and cuddly every time. Now, the butterflies can die. So can the polar bears, if they get in the way of renewables. This is actually expected and is as it has always been. It’s saving what a smaller number of people like (money for free) and destroying that which gets in the way. When the renewable scam ends there will be something new that dictates what gets saved.

February 8, 2020 12:10 pm

So how many insects/birds/mammals/fish are threatened to extinction by CC until they’re not does that make now?

Jeff Alberts
February 8, 2020 12:28 pm

You really need a proofreader, Jim.

Reply to  Jeff Alberts
February 8, 2020 1:12 pm

Please be more specific

Jeff Alberts
Reply to  Jim Steele
February 8, 2020 1:34 pm

I’d rather not clutter the comments up with it. If you like, I can send you an email.

Reply to  Jeff Alberts
February 8, 2020 2:16 pm

@ Jeff Alberts,
When was the last time you wrote a 350 word essay ??
Links ??

Jeff Alberts
Reply to  u.k.(us)
February 8, 2020 2:35 pm

What does that have to do with it? I am trying to help Dr. Steele present his essay to the world. Some people appreciate it, apparently you don’t.

Zig Zag Wanderer
February 8, 2020 12:48 pm

I just saw an eco-loony article stating that we have to provide food drops for a whole year to help wildlife from starving after the (fairly normal) bushfire season here in Oz. Like they never dealt with bushfires before and will all die out because of them now.


Joel O'Bryan
February 8, 2020 1:16 pm

Things in Mexico’s Monarch forest aren’t looking so good right now with the murders of two men involved in the forest-monarch conservation efforts there.

The Liberal NPR can only say they were “found dead.” Like maybe they slipped on a banana peel or something.

One victim: “His body was recovered at the bottom of a holding pond in an agricultural area.

Prosecutors in Michoacán say an autopsy found that the cause of death was “mechanical asphyxiation by drowning of a person with head trauma.”

The 2nd victim: “Raúl Hernández Romero, who had worked as a tour guide in the preserve. His wife reported that he’d gone missing last Monday. His body was found bruised, his head showing trauma from a sharp object.”

Note to NPR, they were murdered.

Reply to  Joel O'Bryan
February 9, 2020 9:22 am

Yeah, but but but, NPR “knows” Mexico is so much better than the US….

Big T
February 8, 2020 1:46 pm

Here in northern lower Michigan, our monarch pop. Saw a big increase also

February 8, 2020 5:38 pm

Thanks Jim – Very logical and informative pair of articles. I find it ironic that human influence may have been the cause of the mammoth Monarch aggregations that have done so much to make the Monarch a conservation icon. Pretty spectacular icon, though, so I hope Mexico finds some way to protect the overwintering sites and the US kills the foolish biofuels subsidy. I’d much rather you yanks paid taxes to set aside land for conservation than to produce expensive, corrosive and mileage-inefficient ethanol.

Reply to  DaveW
February 9, 2020 9:27 am

Unfortunately ethanol is a huge subsidy-industry & very hard politically to end it.

February 8, 2020 5:53 pm

Mr. Steele, Monarchs thrive on the Big Island of Hawaii living and breeding on Crownflower. Crownflower begins as a short bush and if it survives 1-2 seasons of Monarchs it can grow into a 8-10 foot tree…..there are two types, one with white flowers and one with violet flowers. It is very easy to propagate…simply cut a mature branch, place it in water for about 90 days and it will develop prolific roots. Or go to a local Home Depot.

“Loved by monarchs – queens and butterflies alike. That’s the claim to fame of these lavender or white gems of the crown flower. Pua kalaunu was a favorite of Queen Lili‘uokalani; a quilt patterned with the flower adorns her bed at Washington Place, as the long-lasting lei adorned her neck. Crown flower is also the host plant for the monarch butterfly, whose caterpillars gobble up the thick and wooly leaves. Known to botanists as Calotropis gigantea, this large shrub and member of the milkweed family first arrived in Hawaii in 1871. It produces a white, sappy milk that contains calcium oxalate and a cardiac glycoside, two reasons why the crown flower made #5 on the “Top Ten Inquiries About Plants to the Hawaii Poison Hotline.”

February 8, 2020 6:07 pm

“Unfortunately the monarchs main food plants, Common Milkweed and Showy Milkweed, are frost intolerant.”

Plants dying back for the winter is not “frost intolerant”. Only the fleshy part above ground dies back. The roots and tubers wait till the soil warms, again.

Nor are butterflies are active during frost/freeze weather.
It’s kind of odd to frame the topic as if butterflies prosper through winter weather.

Other milkweeds, e.g.; Asclepias incarnata, and Asclepias tuberosa which monarchs happily munch upon in the East are very cold resistant plants.
Asclepias tuberosa USDA hardiness zones 3-9.
Asclepias incarnata is hardy in all USDA hardiness zones.
A hardiness that does not prevent the plant dying back when frosts/freezes occur.

A major problem is that many milkweeds are poisonous to grazing animals.
An easy enough problem if the animal has better grasses/plants available to eat.
A much harder problem if the milkweed is mown, dried and stored as animal fodder.

How It Affects Livestock
An average-sized sheep that eats 30-100 gms of green leaves of one of the more toxic species is likely to die of poisoning. It may die within a few hours or live 2 to 4 days. Although many milkweeds contain resinoids, most of the ones that cause fatal poisonings contain cardenolides (cardiac glycosides). These cardenolides are similar to digoxin causing electrolyte balances in heart muscle resulting in arrhythmias and cardiac failure.”

Farmers used to deal with problem weeds, like milkweed, by turning over the soil at least three times during winter. Turning over the soil exposes weed seeds and roots/tubers allowing them to be killed by the cold.
Modern sprays like glyphosate have only replaced this regimen, not created a new regimen.

Milkweed seeds are easily purchased. Growing the flowers is not a problem.
Milkweed is only a problem when the seeds are allowed to spread uncontrolled.
Downwind milkweed seeds contamination in agriculture areas forces farmers to spray or plow/work fields to remove the unwanted plant. Neither process is cheap or easy.

Conservation Reserve Program (CRP) is funded by funds collected from the Pittman-Robertson Wildlife Restoration Act.

John MacDonald
February 8, 2020 6:17 pm

You are all invited to our little western town of Mariposa, CA for the annual Mariposa Butterfly Festival (okay that’s redundant). My friend Bill organizes it each year for the benefit of school children, tourists and locals. Townsfolk buy butterfly kits and raise them from caterpillars each spring at home and in classrooms. The 2-day festival on May 2-3 has a parade, a vendors row, a butterfly release, a fun run and many other events. This year will feature a cattle drive and jet aircraft flyover. Make your reservations early as we are the gateway to Yosemite Park and hotels fill up early.

Walter Sobchak
February 8, 2020 7:36 pm

“Caruso” by Joan Baez

Now I think I was asleep till I heard
The voice of the great Caruso

Bring infinity home
Let me embrace it one more time
Make it the lilies of the field
Or Caruso in his prime

A friend of mine gave me a tape
She’d copied from a record disc
It was made at the turn of the century
And found in a jacket labeled “misc.”
And midst cellos, harps, and flugelhorns
With the precision of a hummingbird’s heart
Was the lord of the monarch butterflies
One-time ruler of the world of art


Yes, the king of them all was Enrico
Whose singular chest could rival
A hundred fervent Baptists
Giving forth in a tent revival
True he was a vocal miracle
But that’s only secondary
It’s the soul of the monarch butterfly
That I find a little bit scary

February 8, 2020 8:54 pm

This article goes a long way posing and answering some of the same questions I have had. What were Monarch and milkweed numbers before man started plowing up the land and planting crops. What were the numbers before and at the end of the warming that took place in the early 1900s? What were the numbers at the end of the cooling period after that? So much we don’t know.

Crispin in Waterloo
Reply to  Myron
February 8, 2020 9:24 pm


You ask good questions. The idea that agriculture started when the Euro-settlers arrived is of course fiction. The local population was huge in 1500 and their fields where they grew the three sisters (corn, pumpkins and beans) were large.

It quite possible therefore that the milkweed was widespread in Eastern north America before the arrival of the plough.

Walter Sobchak
February 9, 2020 12:05 am

“The local population was huge in 1500”

For some values of huge. The only hard number we have is the 250,000 Indians on the 1890 census. If we posit that number represents a mere 5% of the pre-Columbian population, we imply a population of 5 million. I think the best that can be said is that the likely number is the 7th order of magnitude, i.e. between 3 and 30 million with the likeliest numbers being being less than 10 million.

Since the land area of the continental US is ~3 million sq. mi. The population density was 1 to 2 people per sq. mi. That is really thin on the ground. The modern US has about 100 people per sq. mi.

Much more densely populated areas were found in Central and South America, such as the valley of Mexico and the Peruvian highlands.

February 9, 2020 12:39 am

I think the biggest threat to them are the deadly freezes that their Winter habitat gets. Mexico has had a number of extremely severe freezes that killed a lot of Monarchs – ’96, 2002, and at least one more more recently.
My state has plenty of protected state parks and preserves and they are always setting aside more. Pheasants Forever is buying up buffer areas along rivers and streams and they are loaded with milkweed. I see no shortage of milkweed where here. I think a lot of people simply miss it. I collected some pods again last year and will see if I can get them growing in my garden since I can’t do edibles any more. See if I get any monarchs showing up. They sure like the frog plant I’ve got otherwise.

Steve Richards
February 9, 2020 1:05 am

Isn’t nature good!

Hocus Locus
February 9, 2020 5:47 am

Am I the only one who imagines that Monarch larvae are made of some flavor variation of Neopolitan ice cream?

Andy Pattullo
February 9, 2020 8:18 am

Always love Jim Steele’s sober, insightful and educational explanation of the natural ecology. This level of wisdom and honesty seems rare in traditional academics. That said, my one thought is that the “plight” or not of monarchs seems to fascinate in part simply because of the human fixation with appearance rather than substance. If we were talking about a mosquito or a slime mould that someone felt was in a substantial population decline I doubt so much print (or electrons) would be dedicated to the discussion and understanding. Politics is equally polluted by the fixation over what or who is photogenic or charismatic and not on what or who will build a better society.

As a Canadian I only need point to our current prime minister as an example. Originally described as having boyish good looks, great hair and a famous last name he was felt fit by a majority of the population to govern a whole country in spite of a CV devoid of any relevant skills or experience.

Thus polar bears, monarch butterflies and koalas are meant to be the filter through which we make major decisions on climate, energy and environment and our choices in the voting booth are to be guided by the advertisers in the magazines at the checkout, the celebrity commentators on daytime TV and the photogenic appeal of the contestants. Perhaps our education system needs a bit of tweaking.

February 9, 2020 9:13 am

I have & encourage common milkweeds on the un-mowed areas of my lot & the adjacent lot, but the darn wild grasses are crowding them out. Lost alot of the milkweeds from that, along w/anything other (goldenrod, asters, etc) than the grasses. This may be happening in many areas — grasses are insidious.

February 9, 2020 3:03 pm

There is no subsidy for ethanol it ended 5 years ago and was a 54cent blenders credit. Today the industry is on its own. I do appreciate the monarchs and have planted milkweed and maintained existing plots but state and county governments are a real threat to those efforts

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