The Duck gets it. Prickly pear came out with the First Fleet in an attempt to establish the use of Cochineal beetle as a source of dye. Ironically, another insect that lives on the pear was successfully introduced to control it.
The Cochineal beetle was not a success, but by the 20th century, prickly pear was a serious pest. By the year 1920, prickly pear (mainly Opuntia stricta spp.) infested 58 million acres (23 million hectares) of land in New South Wales and Queensland. It was spreading at an alarming rate of 1 million acres a year when the cactoblastis insect was first released (in 1926). Within six (6) years most of the original pear had been destroyed.