The prickly Pear is a native of America.
It was introduced in Australia in the last century as a garden plant, but soon spread into the wild where it thrived as it was inedible to native wildlife.
By 1928, vast areas had been taken over by the cactus, making the land useless for crops and grazing.
In America the plant is controlled by a moth whose caterpillars feed on the plant. In desperation the Australians brought and released hundreds of these moths into their country. It did the trick. Within seven years a large number of the plants were destroyed and the spread of the cactus was checked.
It was one of the earliest uses of 'biological control' methods.