As the National Wildlife Federation’s first Monarch Butterfly Champion City, San Antonio knows more than most municipalities about the complex relationship between Monarch butterflies and milkweeds. Our town has devoted substantial resources to supporting the Monarch butterfly migration that moves through our part of the world each fall.

But author Anurag Agrawal adds a new dimension to our understanding of the testy relationship between our favorite migrating butterfly and its poisonous host plant. A recipient of the prestigious MacArthur Ecology Award in 2016, the Cornell ecology professor wades far into the milkweeds to make their complicated story highly readable in “Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and their Remarkable Story of Co-evolution“, his new book published by Princeton Press.

Agrawal will discuss the book at the fifth annual San Antonio Book Festival in a session titled From Soil to Sky: How Milkweeds and Monarchs Coexist. The event will take place Saturday, April 8, at 10 a.m., on the first floor of the Central Library. Like all events at the book festival, it is free and open to the public.

Agrawal has always had a bit of a contrarian streak. He was the first scientist to suggest that Monarch  butterfly conservation might be better served if we look beyond planting milkweeds – or anything in the Asclepias family.

“Planting milkweed is probably not a bad thing to do, but it’s not going to increase populations or save them from demise,” he said following the release of a paper in 2016 that explained how the needs of migrating Monarchs change as they make their way south in the fall.

His proposal to increase the planting of late-season nectar plants, which butterflies need to power their fall migration, has been embraced by gardeners and land managers throughout the Monarch flyway, including many in San Antonio.

In his book, Agrawal continues to rock the “Monarchy,” as he fondly calls those who study and follow the Monarch butterfly migration. He peppers the pages with unexpected assertions, like how to cook milkweed stalks for dinner, and this one: Monarch butterflies are simply not great pollinators. Billed as a poster child for pollinator advocacy in recent years, we naturally assume Monarch butterflies to be ace pollinators.

But they’re not, especially for milkweeds, which have an unusual pollinator strategy, similar only to orchids in the natural world. Unlike most flowers, milkweed pollen is not disseminated by individual pollen grains like those we notice clinging to the bodies of bees.

Instead, members of the Asclepias family reproduce via pollinia, evolved pollen packages – sticky masses of pollen that look like tiny yellow bags. Unlike furry bees, Monarch butterflies, because of their size, shape, 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 or its reproductive destination in the female part of the flower.

“This nonpollinating aspect of Monarchs is not widely appreciated,” Agrawal writes. The fact will come as a harsh revelation to many.

Gardeners will love the chapter 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, 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.

But most interesting in this beautifully illustrated book is Agrawal’s intricate description of the continuous one-upmanship that occurs between the iconic creature and its host plant.

As it happens, milkweeds don’t need Monarchs, but Monarchs do need milkweeds. Monarch butterflies will only lay their eggs on milkweeds, a species known for sticky, milky latex sap, which tastes bitter and contains potentially heart-stopping toxins. These poisons protect the butterflies that consume it as caterpillars because it makes them distasteful to predators. 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” that is the premise of the book.

Monarch caterpillar Llano River
As it turns out, Monarch caterpillars need milkweed, but milkweeds don’t need Monarch caterpillars. Credit: Monika Maeckle / San Antonio Report

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 doctorates. That is the greatest strength of this book: making the science understandable to nonscientists.

Join us for From Soil to Sky: How Milkweeds and Monarchs Coexist at the San Antonio Book Festival Saturday, April 8 at 10 a.m. for a conversation and Q&A with Anurag Agrawal. Books will be available for purchase and signing. The event if free and open to the public.

To RSVP, click here. To see a list of the 102 authors visiting the San Antonio Book Festival this weekend, click here. 

San Antonio Report co-founder Monika Maeckle writes about pollinators, native plants, and the ecosystems that sustain them at the Texas Butterfly Ranch website. She is also the founder and director of...