In 1788, prickly pear from the Americas was brought to Australia for hedges and red dye; by the 1920s, it had taken over 24 million hectares of land | World News

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.Why the First Fleet brought a cactus with itThe 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 industry in New South Wales. One of Captain Arthur Phillip’s ships carried Opuntia plants covered in cochineal insects that had come from Brazil. The dye plan was short-lived. The Brazilian insects soon died off, but the cactus plants survived.How a hedge became a crisisThe plants from the First Fleet did not spread much beyond the east coast. New varieties of prickly pear were brought by settlers to properties across Queensland and New South Wales in the mid-1800s and were used for hedges and fodder or animal feed during droughts. The cactus thrived west of the Great Dividing Range, and in many areas it grew so dense that farming became impossible. According to the Queensland State Archives, it overwhelmed native vegetation too. New South Wales passed the Prickly-pear Destruction Act in 1886, followed by further Acts in 1901 and 1924, but none could prevent the prickly pear’s advance. In 1901, Queensland offered a £5,000 reward for an effective method of destroying the cactus, doubled in 1907, but no one claimed it. The moth that saved the dayIn 1913, Queensland organized a team of biologists who traveled to North and South America, where prickly pear is native. They found that insects and plant diseases attacked the cactus there. In 1920, three governments set up the Commonwealth Prickly-Pear Board to study these natural controls. The first two attempts to breed Cactoblastis cactorum in the early 1920s failed, so 3,000 eggs were brought in from Argentina, where the moth is native to a small area.The larvae feed on the soft tissue within the cactus pads and can kill an entire plant in weeks. The first releases of moths were made in 1926. At the height of the program, Chinchilla in Queensland was sending out up to 14 million eggs a day. By 1933, about 80 percent of the infested land in Queensland had been cleared, according to the Queensland State Archives. The museum puts the figure at 50 to 60 percent for New South Wales.Why the story is not overPrickly pear is not gone forever. It is still a problem in New South Wales and Queensland, but not to the crisis proportions of the 1920s, as new varieties that do not act as hosts for the moths have become established. The same moth was introduced to the Caribbean in 1957, where native Opuntia species had never encountered it before.The museum says the moth attacked local species and moved to Mexico, where it has begun destroying the country’s commercial Opuntia crop. There are also serious concerns the moth could damage important Opuntia species throughout the southern United States. The story shows how moving a species to a new place can solve one problem and create another.