The Story of Monarchs and Milkweed Traces Evolutionary Connection

New book published April 11 explores how an insect and plant evolved together


The evolutionary arms race between monarch butterflies and milkweed plants has advanced human knowledge of biology, chemistry, and ecology, and has even led to promising new cancer therapies.

These “royal representatives of all interacting species” are the subject of a new book by Anurag Agrawal, professor of ecology and evolutionary biology and entomology. His illustrated science book Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution, was released April 11 by Princeton University Press.

Agrawal has been studying the dynamic between monarchs and milkweed for over 15 years, but he came to realize that there were vast amounts of information about these organisms that he didn’t know. Monarchs and milkweed, individually and as a pair, have been studied and cherished for hundreds of years, and his book is a celebration of this knowledge.

The monarch butterfly, with its brilliant colors, astonishing 3,000-mile migration, and capacity to survive exclusively on a poisonous plant, has become a mascot for myriad organizations, from the Union of Concerned Scientists to the Monarch Business School in Zug, Switzerland.

In its attempts to protect itself from monarchs, milkweed plants have developed compounds — cardiac glycosides — that, in large doses, can be lethal. But in small doses, those compounds are used to treat congestive heart failure. Recent studies have found that cardenolides also have anti-cancer and antimicrobial properties.

“Milkweeds evolved to protect themselves from predators, such as monarchs, but that co-evolutionary process has had many unanticipated consequences for humanity,” Agrawal said. 

The book is available on Amazon and from other retailers.