Chairman Mao Zedong’s 1958 campaign to eliminate “four pests,” including sparrows, disastrously tipped the ecological balance. Predator-free locusts destroyed crops, exacerbating a national famine that killed millions.
Bounties offered by the government of Tasmania for the Tasmanian tiger played a part in causing the eventual extinction of this apex predator in 1936. The marsupial had been considered a pest in the Australian island-state.
A 20th century federal extermination program nearly killed all gray wolves in the U.S. Their 1995 reintroduction to Yellowstone National Park stopped elk from overgrazing and increased biodiversity.
This appears in the August 08, 2016 issue of TIME.