Monarch butterflies and milkweed. We’ve explored the subject many times right here at the Texas Butterfly Ranch. But author Anurag Agrawal’s recently published Monarchs and Milkweed, A Migrating Butterfly, a Poisonous Plant, and their Remarkable Story of Co-evolution adds a new dimension to our understanding of the testy relationship between our favorite migrating butterfly and its poisonous host plant.
Anurag Agrawal, author of Monarchs and Milkweed, released this spring by Princeton University Press –Courtesy photo
Agrawal, a recipient of the prestigious MacArthur Ecology Award in 2016, wades far into the milkweeds to make this complicated story highly readable. The Professor of Ecology and Evolutionary Sciences and Faculty Fellow at the Atkinson School of a Sustainable Future at Cornell University was the first scientist to suggest that Monarch butterfly conservation might be better served if we looked beyond planting more milkweeds–anything in the Asclepias family. Agrawal proposed increasing late season nectar plants, required by the butterflies in the fall to fuel their migratory flight.
In this beautifully illustrated book, he compares the co-evolution of milkweeds and Monarchs to an “arms race,” a parallel drawn previously by Monarch butterfly expert Lincoln Brower and other scientists.
To Monarch butterfly lovers, the metaphor may seem off-putting, perhaps exaggerated. But after reading Agrawal’s detailed explanation of the continuous one-upmanship that occurs between the iconic creature and its host plant, the label makes perfect sense.
One of Agrawal’s most unexpected assertions: “The butterflies are simply no good as pollinators. Monarchs are strictly pests.” With Monarch butterflies bandied about as the poster child for pollinator advocacy in recent years, we naturally assume that the storied migrants are effective pollinators.
But they’re not. Especially for milkweeds, which have an unusual pollinator strategy, similar only to orchids in the natural world. Milkweed pollen is not disseminated by individual pollen grains like those we notice clinging to the bodies of bees.
The dangling yellow pollen sac is the pollinium of an orchid. Photo via Wikipedia
Instead, members of the Asclepias family reproduce via pollinia, evolved pollen packages–sticky masses of pollen that look like tiny yellow bags. We sometimes see these teeny yellow bulbs attached to bees’ wooly heads or fuzzy legs after they’ve dug into a flower. The pollen sac attaches to the bee. As they dive into flowers, the pollinia somehow is inserted into the flower’s reproductive slit, resulting in pollination.
Monarch butterflies, because of their size, form, and the way they sit atop flowers, simply don’t have the capacity to carry these hefty pollen vessels. And they rarely come into contact with the pollinia, nor its reproductive destination in the female part of the flower.
“This nonpollinating aspect of Monarchs is not widely appreciated,” writes Agrawal.
Now there’s an understatement. Given the Monarch’s Pan-American status as the great pollinator ambassador, that fact will come as a harsh revelation to many.
Agrawal will be in town for a session at the San Antonio Book Festival April 8. Come join us, buy a book, and get it signed.
As it happens, milkweeds don’t need Monarchs, but Monarchs DO need milkweeds. Monarch butterflies will only lay their eggs on plants that are members of the Asclepias or milkweed family, a species known for its sticky, milky latex sap, which tastes bitter and contains potentially heart stopping toxins that protect the butterflies that consume it as caterpillars because it makes them distasteful to predators.
Monarch caterpillars eat the milkweed leaves, morph through their stages, transform into chrysalises, then emerge as adult butterflies. As the Monarchs attack the milkweed by eating it, the milkweed responds by ratcheting up its toxic properties, making the larval food ever more toxic as the season wears on. This is how the plant protects itself and makes for the intriguing “coevolutionary arms race” which is the premise of the book.
Monarch butterflies will only lay their eggs on the toxic milkweed Asclepias species. Courtesy photo
Agrawal notes, and some of us have witnessed first hand, how tiny Monarch caterpillars sometimes perish upon eating perfectly healthy milkweed. The reason may be the milkweed is simply too toxic for the Monarchs to process. As Agrawal points out, “the dose makes the poison.”
In chapter seven, titled “The Milkweed Village,” Agrawal goes into entertaining detail about the 11 different species of insects that have made milkweed “their bed and breakfast.” We’ve seen them all–aphids, milkweed bugs and beetles, wasps, ants. Agrawal introduces each in gory and glorious detail–the “seed eaters,” the “suckers,” the “chewers, miners and borers.” For anyone who raises Monarchs and milkweeds in the garden, many questions will be answered here.
As Monarch caterpillars decimate milkweeds, the plant responds by increasing the levels of cardiac glycosides it produces as a defense. Courtesy photo.
Throughout, Agrawal writes deeply but accessibly about biology, botany, and chemical ecology, only rarely straying into the hyper-scientific jargon that can make such writing impossible to understand for those without PhDs. That is one of the greatest strengths of this book in my view: making the science understandable to nonscientists.
Speaking of eating milkweed, Agrawal also shares that young stalks of certain milkweeds are perfectly edible as a side dish for humans. I had heard this from my friend, hydroponic farmer and adventurous vegetarian Mitchell Hagney of Local Sprout, but had never had it explained.
Anurag Agrawal cooked milkweed for his wife and child. Courtesy photo
Agrawal cites wild plant proponent Euell Gibbons, author of the 1962 classic, Stalking the Wild Asparagus. Young milkweed shoots can apparently be gathered in late spring when they’re four- to eight-inches high, sautéed and served for supper or as a side dish. Agrawal suggests several cold water rinses to remove extreme bitterness from the milkweed but preserve its unique flavor.
“Season with salt, pepper and butter. Serve proudly,” he writes. He offers a color photo of a cast iron skillet filled with young milkweed shoots that he served to his family. The Asclepias veggies appear amazingly similar to asparagus. Perhaps a milkweed cookbook will be next?
Such accessible, fun anecdotes mixed with hardcore science are exactly what make this book a must-read for Monarch followers and generalists alike.
Want to meet Anurag Agrawal? Join us at the San Antonio Book Festival Saturday, April 8, 10 AM, to meet him. We’ll discuss his book and answer your questions. Books will be available for purchase and signing. Hope to see you there! Details here.
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