Amphibians
Cane Toad
Rhinella marina · also called giant toad, marine toad
The cane toad is a large, warty amphibian from the Americas that, in its home range, is an unremarkable part of the ecosystem. Moved to other continents by people, it has become a textbook example of an invasive species gone wrong — and the centre of one of the longest-running wildlife management problems in the world.
Overview
In its native range — from southern Texas through Central America and into the Amazon — the cane toad is a common toad of forest edges, farmland, and gardens, kept in check by predators and parasites that evolved alongside it. Outside that range, in more than 20 countries and territories where it has been introduced, it has few natural checks and has spread aggressively.
Physical characteristics
A cane toad is heavy-bodied and dry-skinned, olive to reddish-brown, with prominent bony ridges over the eyes and a pair of large, kidney-shaped parotoid glands on the shoulders. Adults are usually 10–15 cm long but keep growing throughout life; the record holder, an Australian toad nicknamed “Toadzilla,” weighed 2.7 kg.
The parotoid glands, and smaller glands across the skin, secrete a milky bufotoxin — a defence that works at every stage of the life cycle, from the eggs to the adult.
Why the Australian introduction failed
The 1935 release into the Queensland canefields was meant to control cane beetles. It failed on the biology: the beetles feed at the top of the cane stalks, and adult cane toads are poor jumpers that hunt at ground level. With the target beyond reach, the toads dispersed into every available habitat, breeding in dams, ditches, and puddles, each female producing tens of thousands of eggs a year. From 102 founders they have grown to an estimated 200 million and now occupy a front that is still advancing west and south at up to 60 km a year.
Ecological impact
The main harm the cane toad does is by being eaten. Australian predators had never encountered a large toxic amphibian, and animals that grab a cane toad — northern quolls, monitor lizards, freshwater crocodiles, snakes, and domestic dogs — are frequently poisoned. Some regional predator populations have crashed as the toad front passed through.
The toads also compete with native frogs for food and breeding sites, and their toxic tadpoles poison the water and can wipe out the eggs and larvae of native species in a shared pond.
Management
There is no realistic prospect of eradicating cane toads from Australia. Efforts instead focus on slowing the spread and softening the impact:
- Blocking the invasion route into the arid west by managing artificial water points the toads use as stepping stones.
- Conditioned taste aversion — teaching quolls, goannas, and crocodiles to avoid toads by first offering them small, non-lethal toads or toad sausages laced with a nausea-inducing chemical.
- Encouraging native predators that can already handle toads, and studying the toad-tolerance that some native species are evolving.
- Research into gene-based control, still years from any field use.
Cane Toad: common questions
Why were cane toads brought to Australia?
In 1935, 102 cane toads were released in the Queensland sugarcane districts to control two beetle species whose grubs were damaging the crop. It did not work — the beetles live and feed high on the cane stems, out of a toad's reach — and the toads simply spread out and ate everything else instead.
How toxic is a cane toad?
Very. Glands on its shoulders secrete bufotoxin, a mix of compounds that affects the heart and nervous system. It is potent enough to kill a dog that mouths a toad, and it has caused steep declines in native Australian predators — quolls, goannas, freshwater crocodiles, and snakes — that try to eat this large, unfamiliar amphibian. The eggs and tadpoles are toxic too.
Can anything eat cane toads?
Some animals can. Certain birds flip the toad over and eat only the non-toxic belly and organs; native water rats have learned to cut out the heart and liver; and some snake and lizard populations are evolving smaller heads or a physiological tolerance. Australian conservationists also run "toad aversion" training, feeding predators small toads laced with a nausea-inducing chemical so they learn to leave toads alone.
Are cane toads a problem outside Australia?
Yes. The cane toad is established across the Caribbean, Hawaii and other Pacific islands, the Philippines, and southern Florida, with similar effects on local wildlife and pets, though the Australian invasion is the largest and best documented.