ECOLOGICAL CLEANSING - The New Wild: Why Invasive Species will be Natures Salvation - page 61

insects ( Dactylopius coccus ) that live on them. When squashed, they yield a crimson dye then used in
British military tunics. Until then, rather embarrassingly, the British were dependent for the dye on the
Spanish and Portuguese, who held a world monopoly through their American colonies. But while the
prickly pear enjoyed life in the new British colony, the cochineal insect did not. The result was no dye
but a spreading plague of cacti. The plague persisted and grew for more than a century until government
scientists brought it under control in the 1920s by releasing an Argentine moth that eats the cactus. 29
One danger with introduced biocontrols is that they become too much at home and start eating or
infecting the natives as well. Rather than reestablishing ecological peace, they can become a problem far
more difficult to handle, and more widespread, than the original alien. That happened when the Argen-
tine cactus moth was tried against prickly pears on a handful of Caribbean islands. It has since spread
unbidden into the United States. But the classic case—again in Australia—is the cane toad. Fresh from
success in tackling prickly pear, Australia's biocontrollers decided to take on native beetles destroy-
ing the sugarcane fields of Queensland. In 1935, they brought in a giant South American toad ( Bufo
marinus ) to eat them. The toad had done the same job successfully in the cane fields of Hawaii, the
Philippines, and Puerto Rico. But when Queenslanders released about sixty thousand of them, the toads
largely ignored the beetles, hopped out of the cane fields, and explored their new homeland. They deve-
loped a taste for a wide variety of Australian insects and other invertebrates.
Weighing up to three pounds and measuring up to six inches long, the cane toads were bigger than
the average toad. But the real problem was that they had a gland on the back of their heads that was
highly poisonous to almost anything that tried to eat them. In the toads' homeland, potential predators
had learned to be wary and the glands acted as a deterrent. In Australia, they made a lethal meal for
passing predators who knew no better, like snakes and even freshwater crocodiles.
The innocent locals were massacred in large numbers. The carnage spread as, determined to make
the most of their freedom, the cane toads developed longer legs and headed west. Top Australian natur-
alist Tim Flannery remembers: “A friend of mine was camping on a river in western Queensland when
the toads went through. He went out one evening to fish, and was distracted by a nauseating smell. Fol-
lowing it upstream he discovered a logjam of dead crocodiles. . . . A single toad was enough to kill even
the largest of them.” 30
By the 1980s, the toads had hopped into the Northern Territories and were headed for Kakadu Na-
tional Park, Australia's wildest place. Fears grew of an ecological Armageddon. “Kakadu is lost,” Mike
Tyler of Adelaide University told a breathless media in 2002. “They're going to be more prolific here
than anywhere else, and they're going to get bigger. The cane toad will become the dominant life form
in a little bit of Australia that we thought was pristine.” The predictions seemed to be coming true. 31
Rick Shine of the University of Sydney recalls: “As the toads swept through Kakadu, we saw over
90 percent mortality in large predators like varanid lizards, blue-tongued skinks, freshwater crocs, and
some of the big snakes.” The nation was on toad alert. State governments spent some $17 million in an
effort to halt the toad's advance. Police officers patrolled the borders of Western Australia, using mir-
rors on sticks to check for toads hiding under cars in the way forces in war zones check for explosives.
“Rarely has an invasive animal been so widely reviled by the general populace,” says Shine. Commu-
nity groups sprang up to fight the invasion. Websites like Stop the Toad proliferated. Scientists were
caught up in the panic. “A research program on toad impacts is more likely to be funded if toads are
viewed as catastrophic,” Shine noted later in a sardonic paper on what he came to see as a hysterical
overreaction. 32
All efforts to halt the toads' takeover failed. By 2009, they had reached Western Australia. They now
occupy more than half a million square miles across the north of the country. Yet, says Shine, they are