India, Oct. 10 -- Ever picked up a cute plant on a whim, only to see it take over your balcony? Now imagine that happening on a massive scale. It may sound unlikely, but it happened in Australia. According to the National Museum of Australia, prickly pear had taken over 60 million acres (24.3 million hectares) of land in New South Wales and Queensland before moths were released in 1926 to fight it. That land became unusable for farming. The cactus was first introduced into Australia in 1788, and it was done so on purpose.

The cactus arrived for a colorful reason. Cochineal insects produced a vivid red dye until synthetic dyes emerged in the late 19th century. In the late 18th century, Joseph Banks had suggested setting up a cochineal dye...