• In the 1930s, farmers in Australia were worried about their sugar cane crop, which was being ravaged by the cane beetle. To solve the problem, they imported 102 cane toads from Hawaii. The toads were kept in an enclosure to breed. In 1935, 2,400 cane toads were released into the sugar cane fields of Queensland, Australia, with the hope they would save the sugar cane crop from the cane beetle. It turned out to be an ecological disaster of unprecedented proportion.
• For one thing, cane toads do not eat cane beetles, for several reasons. Cane beetles are active during the day (cane toads are nocturnal). Cane beetles live either under the soil (the toads do not dig) or in the leaves (toads don’t jump.) Adult beetles fly away (toads don’t fly). Cane beetles prefer bare ground (toads prefer ground cover).
• For another thing, there are no natural predators to control cane toad numbers. In addition, they are poisonous. Finally, they breed prolifically.
• Each toad has poison glands on its shoulders which can shoot a milky white neurotoxin up to a yard. In their native Central and South America, predators that evolved alongside the cane toad, such as the caiman, evolved natural defenses against the toxin that the cane toad secretes. Australia’s native species never had time to adapt. A single lick or bite causes native animals to experience rapid heartbeat, excessive salivation, convulsions, paralysis, and often death, usually when the heart stops.
• It’s not only the adults that are poisonous. The eggs and the tadpoles are also toxic.
• Other species of frogs and toads lay perhaps 1,000 eggs at a time, hoping that one or two will survive. The cane toad lays up to 40,000 eggs at a time, and because no creature in Australia can eat those eggs, they all hatch. Then there’s no one to eat 40,000 tadpoles.
• Meanwhile, the tadpoles, and then the voraciously omnivorous adult cane toads, eat all available foods that other creatures depend on, while poisoning everything that tries to eat it, and simultaneously devouring entire populations of frogs, lizards, bugs, and snakes.
• The cane toad is large, growing up to 9 inches, (23 cm) and can easily swallow creatures such as birds and mice. A small marsupial called the Northern quoll has been brought to the brink of extinction. Fresh water crocodiles are experiencing record die-offs after eating the toad. Various species of snake have suffered as well. Turtles and fish that eat the poisonous eggs and tadpoles also die. The cane toad is a single-species ecological wrecking ball.
• Making things worse, cane toads inhabit a wide range of ecological niches including rainforests, coastal mangroves, sand dunes, shrubs, and woodlands. They don’t need much water to reproduce; anything from a puddle to a river is fine. They can survive cold temperatures that kill other amphibians. They begin mating at the age of one year, and can continue to mate for nearly 20 years.
• By 1945, a pesticide had been invented that controlled the cane beetles. By then the cane toad was on the march across the continent of Australia, expanding their territory at a rate of up to 40 miles (60 km) per year.
• However, there is hope. Water rats learned that if they flip the toad on its back, they can avoid the poison. Birds learned that if they harass the toad by flipping it into the air numerous times, and then rinse it in water, they can eat it without harm after it has expended its stores of toxin. Because the toad outpaces the available supply of food, cane toads are now eating smaller cane toads, and larger tadpoles are eating smaller tadpoles. Furthermore, scientists are working to release genetically modified male cane toads that can only have male offspring.
