The Effects of Cane Toads

Back in the mid-1930s, Australian sugar cane farmers struggled to control two beetle species whose larvae ate sugar cane roots and ravaged crops. Beetle infestations had long plagued sugar cane plantations worldwide, and over the previous century, farmers had introduced cane toads into cane-growing areas in the hope that the toads would eat the beetles. After the first shipment of cane toads landed in North Queensland in 1935, Australians soon regretted the decision to introduce them. Large, hungry and aggressive, the toads spread rapidly, destabilized native ecosystems and poisoned unwary pets, humans and predators.

  1. Competing Against Native Animals

    • Cane toads proved very adaptable to tropical areas in northeastern Australia. Some scientists suggest that large numbers of cane toads can drive down insect populations so much that native insectivores, particularly lizards, go hungry. Evidence suggests that because most native frogs live in trees, they do not compete directly with ground-dwelling adult toads, but the toads' voracious appetites may put pressure on frogs during other life cycle stages.

    Poisoning Predators, Pets and People

    • Most Australian animals have little immunity to the unfamiliar toxins the toads secrete at all stages of their life cycle. As eggs and tadpoles, they poison many aquatic species, and once they move onto land as juveniles and adults, they can be deadly to snakes and other predators who mistake them for nonpoisonous native frogs. One researcher speculates that "cane toads may have been the nail in the coffin for many populations," including quolls (catlike marsupials), goannas (monitor lizards) and rare snakes. Domestic dogs have also died from picking up cane toads in their mouths, and while Australia has recorded no human deaths from cane toad poisoning, people have died elsewhere from eating them by mistake.

    Eating Important Native Species

    • Though farmers worldwide imported the toads to deal with beetle infestations, one profile notes that "introductions played out with the toads turning their noses up at the sugar cane beetles in favor of anything else they could jam into their sizable mouths, including all kinds of invertebrates, other amphibians, reptiles, birds, and small mammals." Cane toads show a special appetite for commercially important honeybees, and one study found that toads targeted the hatchlings of rainbow bee-eaters, a bird that nests in underground tunnels.

    Expanding Ranges and Multiplying Numbers

    • Residents of Townsville, Queensland collect cane toads during an annual cull.

      Like other introduced or invasive species, cane toads spread quickly in environments with abundant food and few natural predators. In Australia, their range now extends across a large swath in the northern part of the country, despite efforts to contain them. They can lay tens of thousands of eggs during each reproductive cycle, quickly replacing toads killed under bounties or culling policies. Cane toads now hop south and west, invading more vulnerable ecosystems where they eat native wildlife and poison predators not yet familiar with their toxic effects and terrible taste.