In the late 18th century, cactus plants—likely including a species known as Opuntia monacantha—were brought to Australia, with the first group arriving in 1788. By the 1840s, these plants, commonly called Barbary figs or prickly pears, were intentionally planted by Australian farmers as natural fences and a food source for livestock during droughts. Additionally, they were used to produce cochineal dye, a bright red pigment derived from insects that was used to color British military uniforms. However, by the early 20th century, the cactus had become an invasive species, taking over large areas of farmland and making them unproductive. It spread rapidly, covering about 404,686 hectares per year in the early 1900s, and by 1919, it was spreading at a rate of one million acres annually. Efforts to control the cactus through manual removal, chemical treatments, and fire were largely ineffective, as the plant's stems could regrow after being cut. In 1901, the Australian government offered a reward of 5,000 pounds for an effective control method, which was later increased to 10,000 pounds in 1907. However, the reward was never claimed, as no method proved successful. In 1912, Australian researchers began a systematic search for biological control agents—organisms that could naturally reduce the cactus population. After testing 52 species, they released 18 insect species and one mite species in Queensland, hoping they would target the cactus. Among these, the Cactoblastis cactorum moth, a small gray-brown moth native to South America, proved to be the most effective. The moth's larvae feed on the inside of the cactus, destroying it from within and leaving only hollow shells. In 1926, 3,000 Cactoblastis cactorum eggs were imported from Argentina, and the moth population grew rapidly. By 1930, nearly 3 billion eggs had been distributed to farmers in Queensland and New South Wales. The results were extraordinary. By 1933, it was estimated that 80 percent of infested lands in Queensland and 50 to 60 percent in New South Wales had been cleared of the cactus. This success is considered one of the most remarkable examples of biological control in the world. In recognition of its role, two towns in Queensland, Dalby and Boonarga, have erected monuments honoring the moth. However, the cactus was never fully eradicated and continues to appear sporadically in some areas. Later, the same moth was introduced to the Caribbean and the southern United States, where it now threatens native cactus species in Florida. The Australian experience shows that even highly effective biological control methods can have unexpected and sometimes harmful consequences in new environments.