Exotic Down Under

Australia Fights Back Against Invader Species

The nearly one-foot, 10-pound cane toad might strike visitors to Australia as just one more example of the country’s notoriously bizarre fauna. In reality, this amphibian is not native, but one of many human-introduced species currently ravaging the ecosystem “down under.”

Originally from South America, the cane toad was introduced by the sugar industry in 1935 in a misguided attempt to control two sugarcane pests: the Grey Backed cane beetle and the Frenchie beetle. Unfortunately, no one noticed that the toad doesn’t generally eat these bugs, though it successfully devoured other native insects and micro-fauna to the point of extinction. Adding insult to ecosystem injury, the poisonous toad instantly kills any predator that attempts to eat it, particularly the quoll, Australia’s marsupial cat, and giant native lizards. Its population continues to proliferate, outcompeting native amphibians and spreading disease.

Sheep by the millions join with rabbits, foxes, cane toads and even prickly pear cactus to despoil the natural flora and fauna of Australia.Mitsvaki Iwago/Minden Pictures

The cane toad is not an isolated incident for Australia, but disturbingly typical of the ecological problems on the island continent. Australia’s native wildlife is almost entirely endemic, having evolved in virtual isolation from the rest of the world. The fauna includes an impressive array of exotics—koalas, kangaroos, duck-billed platipi, wallabies—but no placental mammals or high-level predators. The first introduction by humans was probably dingoes, brought by early aborigines in the form of pets almost 7,000 years ago. Larger introductions began with European colonization in the mid-1800s. Colonists thought the ecosystem “badly flawed” because it lacked the wildlife to which they were accustomed, and so stocked the country with deer, rabbit and pheasant to provide favorite foods, foxes for hunting, and a wide variety of other species for sheer familiarity. In the words of Chris Bright, bio-invasion researcher and author of Life Out of Bounds, “the effort proved a disastrous success.”

One notable disaster occurred in 1859 when British colonist Thomas Austin imported 24 rabbits for sport hunting. As Australian author William Lines notes, they “acclimatized to the Australian environment with frightening fecundity.” The population quickly exploded to more than 200 million, devouring native grasses, brush and tree sprouts, and turning grassland and farmland into dusty desert. Cattle, goats and sheep exacerbated the problem with relentless grazing, resulting in diminished food, no brush hiding places and fewer burrows for small marsupials such as the hare wallabie, the bilbie and the bandicoot. Their populations crashed.

Troubles continued from another introduced predator, the European Red Fox, which proved itself highly effective, preying on native mammals too big to hide in the ground and too small to defend themselves, like wallabies and rat-kangaroos. According to the University of Queensland’s Hamish McCallum, this fox/rabbit duo has been, “a deadly combination,” for Australian wildlife, “decimating the population of endemic mid-sized mammals—wherever foxes and rabbits have appeared, native mammals have vanished.”

Many efforts have been undertaken to control these invaders, particularly the rabbits, which cause approximately $20 million annually in agricultural damage alone. Exclusion fences and poisoning require constant maintenance, however, and are often overwhelmed by the rabbits’ astronomical reproduction rates. In the 1950s, the government released a disease called Myxomatosis, which killed 90 percent of the animals it infected—an ideal solution until the rabbits recovered and developed a resistance. Moreover, the disease carrier, a flea, can’t survive in the arid conditions of much of the country, and so the Australian Animal and Plant Control Commission was forced to introduce an even hardier Spanish flea. Now a new infection—Rabbit Calicivirus Disease—doesn’t require a carrier, but poses the danger of breeding more robust, resistant rabbits, possibly infecting native animals and people.

According to Bright, “Biocontrol will never be a panacea,” but is still “the best candidate” for control in some situations. In comparison to other programs, at least, it is often remarkably effective, and less labor intensive. The most effective solution to the cane toad problem has been the surreal “Chill a Toad” program—which involves catching, refrigerating and killing these invaders one by one.

While larger animals may be the most obvious alien invaders, they are hardly alone. According to the Australian government, “almost 10 percent of all the plant life in Australia is alien to the country.” The most infamous example—the prickly pear cactus—was brought over in the early 1900s as a hedging plant to keep livestock under control. It quickly ran wild, overtaking the Australian desert, but was eventually checked by the introduction of the Cactoblastis, a cactus-hungry Mexican moth.

The European Zebra Mussel, which caused billions of dollars of damage to America’s Great Lakes, has now shown up in two of Australia’s ports, most likely transported there by foreign ships. The Australian government responded by chlorinating the entire marina where the mussels were sighted. While it is still not clear if the chlorination killed all the Zebra mussels, it did kill vast amounts of native coral, fish and marine invertebrates.

As long as wildlife still exists, some people may wonder why we should care if one animal or plant replaces another? “Most Australians have never heard of our worst invaders,” says Tim Low, author of Feral Future. The answer is common sense: Introduced wildlife often changes habitat and sets in motion negative long-term effects. For example, the overgrazing of rabbits and cattle causes erosion, which will eventually make land unsustainable for any type of growth, including agriculture. Likewise, fisheries will disappear with the continued destruction of coral reefs.

Even if practical concerns can be overcome, bioinvasion will still have consequences—unchecked, it will ultimately mean extinction of Australia’s exotic wildlife, and destruction of a major ecosystem. The ecological disaster that follows will be marked only by absence: Brilliant Australian frogs will be gone, outcompeted by the cane toad; bright corals will have succumbed to repeated chlorinations; bilbies will perish without burrows and wallabies will be eaten by foxes. Where is the allure in being “down under” if “down under” is no longer different from your own backyard?