Throughout the nineteenth century, swarms of locusts regularly swept across the continent, turning noon into dusk, demolishing farm communities, and bringing trains to a halt as the crushed bodies of insects greased the rails. In 1876, the U.S. Congress declared the locust "the single greatest impediment to the settlement of the country." From the Dakotas to Texas, from California to Iowa, the swarms pushed thousands of settlers to the brink of starvation, prompting the federal government to enlist some of the greatest scientific minds of the day and thereby jumpstarting the fledgling science of entomology. Over the next few decades, the Rocky Mountain locust suddenly -- and mysteriously -- vanished. A century later, Jeffrey Lockwood set out to discover why. Unconvinced by the reigning theories, he searched for new evidence in musty books, crumbling maps, and crevassed glaciers, eventually piecing together the elusive answer: A group of early settlers unwittingly destroyed the locust's sanctuaries just as the insect was experiencing a natural population crash. Drawing on historical accounts and modern science, Locust brings to life the cultural, economic, and political forces at work in America in the late-nineteenth century, even as it solves one of the greatest ecological mysteries of our time.