How One Plant Murdered a Continent

Source: How One Plant Murdered a Continent, Make Thing With Hand, 18:32, uploaded 2026-06-15, playlist index 20.

Make Thing With Hand opens beside a prickly pear cactus in the southwestern United States. The plant belongs to the genus Opuntia. Native bees pollinate it, tortoises and birds eat it, and the video presents it as part of the desert’s ordinary social life. The same cactus became one of the most destructive plants in Australia’s history after people carried it across an ocean and left it in a place where its old checks did not follow.

An American cactus in Australia

The native range of Opuntia runs from 56° north in Canada through South America. The video lists the deserts of Mexico, the Caribbean, Central America, the American Midwest, the eastern United States, and the Galapagos among its habitats. Blue-footed boobies in the Galapagos lay their eggs on bare rock because they have lived for thousands of years without ground predators. The example gives the cactus a setting full of relationships that formed over time.

Australia had no native cacti when prickly pear arrived in 1788. The video says a ship carrying settlers brought it in, where people valued the plant as an attractive ornament that grew easily in an arid climate. The experiment worked. By the early twentieth century, the cactus had escaped cultivation and spread across 20 million hectares of countryside at a rate of more than a million hectares a year. The spiny growth made farms and homes unusable, overtook cultivated fields, and broke up communities. The video cites more than 10 million hectares of abandoned farms and describes the result as a “horror of spines”.

Prickly pear survived almost every attempt to remove it. Drought, flood, fire, poison, grazing, and chopping often left it stronger. A root, pad, bud, fallen fruit, or flower could produce another thicket, while birds carried the seeds farther. People could not bury it or burn it into submission because the fragments grew again.

The Australian government offered a reward that the video values at $600,000 in today’s Australian money. About 700 proposals followed. After the government doubled the reward and waited more than five years, the suggestions included mustard gas, flamethrowers, and the release of more rabbits. Australia also put bounties on emus, crows, and currawongs because the birds spread prickly pear seeds. The bounty was claimed more than 300,000 times. None of this solved the problem. Three million kilograms of arsenic pentoxide and sulfuric acid went onto the land, and the cactus kept growing.

The plant did not need to be a genetically modified super-cactus or a biological weapon. The video insists that it was an ordinary cactus placed in a new ecological setting. The campaign paused during the First World War. When Australian soldiers returned, the domestic infestation remained, and a joint task force began looking for a biological answer.

The danger of importing a solution

The proposed answer was another non-native species. The reasoning had a clear shape: find an organism that attacks the first invader in its original home, bring it to Australia, and let it do the work that fire and poison could not. The video interrupts this plan with Hawaii, another isolated landmass whose separation has allowed unusual forms of life to develop.

In 1936, Hawaii received the giant African snail, Achatina fulica. The agricultural pest had no natural enemies on the islands. In 1955, officials introduced the rosy wolf snail, Euglandina rosea, from Central America to prey on it. The wolf snail found other prey more easily. Hawaii once had about 700 endemic snail species, according to the video. Roughly 90 per cent have since gone extinct, while many of the survivors remain close to extinction.

The example gives the Australian plan its danger. A predator arrives with a target in mind, then encounters a whole world of animals that have never evolved around it. The video compares this to bringing a gun to a knife fight. Australia and Hawaii have isolated histories, and that isolation has produced life found nowhere else. The video reports that nearly half of Australia’s birds, 69 per cent of its mammals, 93 per cent of its amphibians, and 94 per cent of its reptiles are endemic to the continent. Isolation creates distinctive life and leaves it exposed to organisms that arrive with unfamiliar weapons.

The video briefly brings that problem into the present. It mentions Utah’s reported plan to exchange remaining water, perhaps including the shrinking Great Salt Lake, for a data-centre partnership with Canadian businessman Kevin O’Leary. The proposed centre would be twice the size of Manhattan. The aside is comic, yet it returns to the same question: an environment can appear suitable for a profitable introduction while carrying costs that the first plan leaves outside its frame.

What makes a cactus difficult to stop

The biological reason for prickly pear’s success begins with water. Cacti store water in their thick stems, which also perform photosynthesis. Their areoles are the growing points from which spines and new growth emerge. Spines are modified leaves. They protect the plant from herbivores and reduce surface area and airflow, which limits water loss.

Cacti also open their stomata at night. These small pores let the plant exchange gases while cooler air reduces the amount of moisture lost through transpiration. Pineapple, agave, and euphorbia use related forms of night-time water conservation, so the trait belongs to a wider family of drought adaptations. The video gives a full-grown saguaro’s ability to absorb as much as 760 litres in one storm as another measure of the advantage.

Those adaptations do not make cacti invulnerable in their home ecosystems. Cochineal scale insects attach themselves to the plant, cover their bodies with protective secretions, and drain the infected parts until they die. Pronghorn, woodrats, cottontails, jackrabbits, bison, peccaries, and bobwhites also eat prickly pear, along with the tortoises and birds from the opening. The native range contains predators, grazers, insects, and competitors that limit the plant’s spread.

The Australian task force had a more specific option. A moth native to Argentina, Cactoblastis cactorum, attacks prickly pear. The moth and cochineal insects could form the one-two response that the earlier campaigns lacked. Australia introduced the moth in 1925 and distributed its first 10 million eggs over the following years. By 1930, more than 3 billion eggs had been released.

The result looked miraculous. Prickly pear segments carrying cochineal reportedly sold for as much as $20,000 in today’s Australian money. In 1936, Australia declared the invasion overcome. By 1940, the video says, 95 per cent of the invasive cactus had disappeared. The giant mass of spines collapsed within a few years, and the biological method worked so well that it encouraged later attempts to solve other ecological problems with introduced species.

Context travels with a species

The same moth that controlled prickly pear in Australia now threatens cacti in parts of the United States, where people consider it invasive. Its effect changes with the setting that receives it. The host, its enemies, the available prey, and the local history all shape what an organism can do.

The video gives invasive species a place just below habitat loss among the causes of species decline. It ends with actions available to an individual: plant native species, learn which exotics to avoid in a garden, and help remove invasive plants. Those actions are modest beside a continental infestation, yet they follow the video’s larger claim that introductions carry ecological context with them. A plant that supports a desert community can become a wall of spines when the relationships that contained it remain on another continent.

Limits

The video supplies no bibliography or links for its historical figures, species counts, prices, or claims about the ranking of invasive species among causes of biodiversity loss. This note keeps those figures as claims made by the source rather than presenting them as independently checked facts. The Hawaii snail story and the Australian moth campaign carry the main comparison, while the Utah data-centre passage functions as a current-news aside whose factual details also remain sourced only to the video. The description credits archival footage to NFSA Film Australia.

Further reading / references

• The video description credits archival footage to NFSA Film Australia.