Monarchs and Milkweed

February 15, 2017
The relationship between monarch butterflies and milkweed plants, a story that is "much more...than bright coloration and a penchant for epic journeys."The monarch has an abiding fascination for scientists and nature lovers alike. An individual North America monarch may fly up to 3,000 miles from Mexico to Canada annually. Along the way, it will lay eggs on milkweed, which provide sustenance for the next generation of emerging caterpillars. Milkweed is toxic to sheep and horses but crucial to butterflies. Agrawal (Ecology, Evolutionary Biology, Entomology/Cornell Univ.) explains how the monarch and milkweed, both native to North America and likely dating back millions of years, "share a deep evolutionary history." Their relationship is an example of "coevolution," and the author shows how they "have spent millions of years evolving chemical traits and reciprocally coevolving in a manner that puts chemistry at the center of their arms race." Birds that would otherwise feed on monarchs are made nauseous if the butterflies have fed on milkweed and therefore quickly learn to avoid them. In the course of their annual, cross-country flight, the monarchs lay their eggs on the plants, providing shelter, food, and safety for their caterpillars as they emerge. The author describes the extraordinary appetite of these monarch caterpillars, whose birth weight is comparable to that of a bread crumb but whose mass quickly increases more than 200 times in the first two weeks of its life. Over time, monarch butterflies have become impervious to the toxins released by milkweed to deter pests. In response, the plant has evolved an alternate strategy, releasing a blend of volatile compounds to attract wasps that feed on the caterpillars. As Agrawal accessibly demonstrates, this is exemplary of the arms race between predator and prey, which is an important driver of evolution. A lively, highly informative introduction to significant research in ecology that highlights the importance of conserving our natural habitats.

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March 1, 2017

Don't be fooled by the delicate beauty of monarch butterflies and milkweed: a war has raged for millions of years. Monarch caterpillars eat only milkweed, a toxic plant that continuously evolves to discourage consumption. The monarchs persist, as the poison makes them literally sickening to their predators. Agrawal (ecology, evolutionary biology, & entomology, Cornell Univ.; coeditor, Insect Outbreaks Revisited) offers historical evidence and current research to explain the relationship between the two. Many visuals, such as graphs and pictures, aid the text, making the book reminiscent of a college seminar. The author's style is accessible as he stops to explain unfamiliar terms and background. However, only readers with a strong interest in butterflies and milkweed or those committed to lifelong learning will likely stay motivated to finish this volume. There has been much media coverage of the declining monarch population, with suggestions to plant more milkweed. Yet Agrawal believes that an alleged lack of milkweed isn't the real problem. He cautions that many of his peers don't agree with his theory but encourages others to figure out the mystery. VERDICT Interesting, but for a specific audience.--Elissa Cooper, Helen Plum Memorial Lib., Lombard, IL

Copyright 2017 Library Journal, LLC Used with permission.

March 15, 2017
The monarch butterfly has long been celebrated among entomologists and nature lovers, not only because of its striking, tiger-like, black-and-orange stripes but also for its heroic annual migration from the Northern U.S. and Canada to as far south as Mexico, often covering thousands of miles. This comprehensive and colorfully illustrated study of monarch biology and behavior by Cornell University entomology professor Agrawal offers another reason to admire the versatile insect: its long and successful symbiotic relationship with the otherwise toxic milkweed plant. In giving milkweed a featured role in the monarch's biological history, Agrawal highlights the remarkable ways the two species have evolved together, competing in a virtual arms race that has benefited both plant and butterfly. To repulse predators like monarchs, the milkweed has evolved to produce poisonous cardenolides, while the monarch has ingeniously learned to incorporate the bitter cardenolides into its wing membranes to fend off ravenous birds. Agrawal's book will appeal not only to butterfly enthusiasts but also to the environmentally aware and all readers who appreciate solidly written and accessible popular science.(Reprinted with permission of Booklist, copyright 2017, American Library Association.)