What to do about the decline of the monarchs? The recent
Thanksgiving count in California was dire. The spiral in eastern north America is no better. The monarchs need many things, and milkweed is absolutely essential. It is the only plant their caterpillars eat. And as described in my book, , the two share an intimate and antagonistic evolutionary history. While monarchs continually evolve to keep up with milkweed, milkweed too constantly evolves better and better defenses. But, in Europe, where the common milkweed ( Monarchs and Milkweed ) was introduced over 400 years ago, there are no monarchs. What follows below is part travel log, part natural history diary, and part historical journey regarding milkweeds and their bugs in Europe. At the bottom, I end with a modest proposal for what we might do. Here we go. Asclepias syriaca
has about 140 species (in the botanical family Asclepias Apocynaceae), with >90% from temperate North America, and the lion’s share of them in Mexico and the SW USA. Click here for a visual smattering of milkweed floral diversity. Only a handful are tropical, from Central America and northern S. America. Although sometimes controversial, the sister to Asclepias, is a genus of >200 old-world species, all in Africa. But, Gomphocarpus Asclepias does have a history in Europe, an unnatural history that starts >400 years ago. But I am getting ahead of myself. My exploration of Asclepias in Europe started with research for , continued with a Monarchs and Milkweed research project on evolution of introduced milkweed in Europe, and most recently culminated with a trip to Hungary. Let me start with the last first.
In August 2018, I headed to Budapest to attend the International Society of Chemical Ecology‘s(ISCE) annual meeting, where I was a featured speaker, having just been awarded the Silverstein-Simeone Award.
As you might expect, I gave a lecture on Monarchs and Milkweed, although it was slightly unnerving to have the ISCE executive board with me on stage as I gave my talk.
Perhaps the most special part of the conference for me was meeting up with four past post-doctoral scholars, all highly successful chemical ecologists: Jared Ali (in the back), and left to right in front: Sergio Rasmann, Tobias , and Züst Georg Petschenka.
Hungary is famous for is paprika and other preparations of peppers (which are native to central America)
Georg and I in front of the Hungarian Parliament Building on the Danube.
The other highlight was a field trip to look for America’s common milkweed, Asclepias syriaca, an introduced plant which is abundant (but not “invasive”) in the Hungarian countryside.
Remarkably, milkweed grows with a common friend, also native to N America, tall goldenrod ( Solidago altissima), and these meadow plants grow among corn and sunflower agricultural fields here outside of Budapest.
We couldn’t translate it, but it didn’t seem good. And rather un-European!
With Georg and my friend and colleague John Maron from the Univ. of Montana
Pentatomid bugs (stinkbugs) are common on milkweed in N. America and Europe.
The European milkweed fauna has a familiar face, here is Lygaeus equestris, a close relative of our N. American L. kalmii. In Europe, L. equestris, typically feeds on species (also in the milkweed family). Cynanchum
Tobias Züst looking for aphids
And here they are, a familiar tri-trophic interaction: milkweed, the oleander aphid ( Aphis nerii), and a ladybug. Aphis nerii is a aposematic (brightly colored) aphid that eats nearly all milkweeds and is found on six continents.
Flowers were sparse mid-August, as most plants had already gone to seed. There are no monarchs in Europe… although one seems to make it across the Atlantic every few decades. So far, their populations are not self-sustaining here, although there are established monarch populations in nearby Spain.
Two other cool plants from our jaunt in the Hungarian countryside. First, a remarkably spiny herb from the carrot family (Apiaceae) in the genus Eryngium.
Tobias also found a cardenolide-containing mustard (A wallflower in the genus ) … although the bulk of plants that produce these toxic heart-impacting compounds are in the milkweed family, several other groups have evolved a small set of plants with them. Erysimum
Now, on to some of the earlier history. To understand how the common milkweed got its scientific name “ Asclepias syriaca” we must travel back in time over 400 years… and examine plants that were transported from eastern Canada to Paris.
In the 1700s, Carolus Linnaeus named the milkweed genus “Asclepias” after the Greek god of medicine Asklepios, son of Apollo (photo by Segio Rasmann). Linnaeus gave this name because he was well aware of milkweed’s medicinal properties. But the story of common milkweed’s name is a little complicated…
In his 1753 opus , Linnaeus recognized that Species Plantarum A. syriaca was a New World plant native to eastern North America, but he decided to keep an old species name (probably for consistency). The “syriaca” epithet was given because the original namer, Jacques-Philippe Cornuti made a mistake in 1635. Here in the Paris Botanical Garden, Cornuti examined the plant we now call common milkweed (imported from eastern Canada few years earlier) and concluded that it was the same species then called “Beidelsar” a plant known from the Middle East that had been classified as Apocynum syriacum by Carolus Clusius in 1601.
Common milkweed in the Paris Botanical Garden 2018… not many bugs, just some aphids and ladybugs. Where are the monarchs?
A page from . Linnaeus could have straightened things out, had he realized that Cornuti had confused the two plant species as one. But, Linnaeus was unaware of Cornuti’s mistake, and unaware that Clusius had already classified Beidelsar as Species Plantarum Apocynum syriacum. In my humble opinion, Linnaeus should have kept the species name syriaca for Beidelsar, retaining some historical precedence and a geographically correct name, but he apparently did not check his sources closely enough 😉
Calotropis gigantea, photo taken in Madagascar
Calotropis gigantea, had seen the flowers, presumably he wouldn’t have made the mistake. Interestingly, monarchs can grow and develop on Calotropis, and it is used widely as a ornamental as well as rearing plant for monarchs in Florida. Across much of Africa, Jacques-Philippe Cornuti Calotropis is fed upon by the “African Queen” a close relative of the monarch. Danaus chrysippus
So where does this leave us? Monarchs are declining precipitously in their native range, in eastern N America and in the semi-independent population in California. Yes, where milkweeds have been introduced elsewhere, typically as ornamentals, monarchs have found them and established self-sustaining populations. In Spain and Hawaii (and Florida, where they are native), monarchs are non-migratory. While in other newly introduced places such as New Zealand and Australia, monarchs have established new migratory patterns. Who knew!
A modest proposal. So what about it? …. Perhaps we should introduce monarchs to Europe. Maybe there too monarchs could establish on the milkweeds that were introduced over the past 400 years. Extra insurance for our beloved and declining butterfly? But what would the ecological consequences be? Unintended side effects? Could this insurance policy actually help reverse the decline. Almost certainly not. Most of the proposed band-aids, mass rearing and the like, ignore the real problem. If as many of have speculated, monarchs are sentinels for the health of our continent, then we should take their decline as a wake up call, not as a call to arms to fix this one small problem.
Thanks for reading! And to leave you, here is a picture from the awards ceremony (October 2018) where Amy Hastings, the Research Support Specialist in my lab received a college-wide award for all of her excellent contributions over the past 10 years! Congratulations Amy, so great to work with you!