Cane toads have spread across northern Australia and into the Kimberley wilderness since their introduction in 1935, causing significant harm to native wildlife. Local rangers and researchers are now studying how some predators are adapting to survive alongside them.
For decades, eating a cane toad in Australia was almost certainly fatal for native animals. The toads carry potent toxins in glands behind their heads, and many species that attempted to eat them died as a result. Goannas, quolls, snakes, and freshwater crocodiles were among the hardest hit.
In April 2016, a small saltwater crocodile in the Daintree River caught a cane toad, held it in its jaws for about 25 minutes, and then swallowed it. Five days later, the same crocodile was observed eating two more toads. This behavior was documented by David White, a river guide with nearly 30 years of experience on the Daintree, who photographed the events and sent the images to Professor Rick Shine, a biologist who has studied cane toads for decades.
The photos raised a question that researchers had not seriously considered: whether some Australian predators were quietly developing the ability to survive encounters with cane toads.
The toads were brought from Hawaii to Queensland in 1935 to control beetles that were damaging sugarcane crops. The plan failed because the beetles lived high on the cane stalks, out of the toads’ reach. The toads instead ate insects, small reptiles, other frogs, and pet food. They reproduced rapidly and spread across Queensland, the Northern Territory, and into Western Australia, eventually occupying more than one million square kilometers.
The main problem was not what the toads ate, but what happened when native animals ate them. The toads’ parotoid glands contain toxins that affect the heart. When a predator bites a toad, the glands release a milky poison into the predator’s mouth, often causing seizures, heart failure, and death within minutes. Australian wildlife had no evolutionary warning system for these toxins, since no native Australian frogs belong to the same family.
As the toads advanced, predator populations collapsed. Control efforts have included hand-collecting toads at night, traps funded by local councils, fencing around water sources, and community hunting events. The estimated cost of environmental damage and control programs has been put at around 200 million dollars per year. None of these efforts have stopped the spread.
A single female cane toad can lay up to 30,000 eggs at a time, multiple times a year. That reproductive rate has outpaced every control method tried so far.
Some researchers have explored whether cane toads could be used against themselves. In crowded breeding pools, larger cane toad tadpoles eat the eggs and young of their own species. Scientists have developed genetically modified tadpoles that never mature, remain in the water longer, and continue eating cane toad eggs until they die without reproducing. The project is still in development.
Government agencies in multiple states, including Western Australia, have acknowledged that cane toads cannot be eliminated and that the realistic goal is reducing the damage they cause.
At Fogg Dam, a wetland near Darwin, researchers tracking cane toad populations observed a dramatic decline over 27 months. Numbers fell by about 98 percent along surveyed routes. Weather records did not explain the drop. What researchers noticed instead was a breeding population of saltwater crocodiles in an area where they had rarely been seen before. No one could confirm that the crocodiles caused the decline, but the possibility drew attention.
Saltwater crocodiles are the largest living reptiles. Large males can exceed 17 feet and weigh more than a ton. Their bite force is among the strongest recorded for any living animal. This creates a problem when eating cane toads: the harder the bite, the more toxin is released from the toad’s glands.
Yet long-term surveys in northern Australia have never recorded a decline in saltwater crocodile numbers in areas invaded by cane toads. Freshwater crocodiles, large lizards, marsupials, and many snakes suffered severe losses. Saltwater crocodiles did not.
One possible explanation is evolutionary history. Saltwater crocodiles range across northern Australia, New Guinea, Southeast Asia, and parts of India. Their ancestors lived in regions where toxic frogs related to the cane toad have existed for a very long time. Over many generations, crocodiles that tolerated small doses of frog toxin were more likely to survive and pass on their genes. Modern saltwater crocodiles may carry some inherited resistance.
Freshwater crocodiles, by contrast, evolved in isolation in Australia, where no toxic frogs existed until cane toads arrived. They had no resistance and died in large numbers when they ate the toads.
Behavior also appears to play a role. The crocodile in the Daintree did not swallow the toad immediately. It shook its head, struck the toad against rocks, dragged it underwater, and held it for 25 minutes. Other saltwater crocodiles have been observed doing the same. This behavior may serve to release the toad’s toxin into the water rather than into the crocodile’s mouth, where it would be absorbed. The crocodile’s large body size also helps, since the same dose of toxin affects a larger animal less severely.
This washing behavior is not a technique invented specifically for cane toads. It is the same way crocodiles handle other prey. Against cane toads, it strips away the toad’s main defense.
Saltwater crocodiles were nearly wiped out by hunting after World War II. The demand for crocodile skins created a large industry along northern Australian rivers. Hunters used spotlights to find crocodiles at night, shot them, skinned them on the spot, and shipped the hides overseas. Small crocodiles were also killed, often by locals who saw them as dangerous. By the early 1970s, saltwater crocodile numbers had fallen so low that the animal required legal protection.
Protection was introduced in the early 1970s, and over the following half-century, saltwater crocodiles gradually returned to rivers, estuaries, and wetlands. The Northern Territory now has one of the largest wild populations of saltwater crocodiles in the world.
The recovery created new challenges. Crocodiles began appearing near towns, boat ramps, fishing spots, and swimming areas. Encounters became more frequent, and some ended in tragedy. Authorities have removed hundreds of crocodiles in recent years. In one community in the Northern Territory in 2024, a crocodile was removed after approaching residents. That year, 239 crocodiles were removed from the surrounding area, with the highest annual number reaching 390 in 2018. Many of these animals had not harmed anyone.
Even with their ability to eat cane toads, saltwater crocodiles cannot solve the toad problem on their own. The toads’ reproductive capacity is simply too large. Even if every saltwater crocodile in northern Australia ate dozens of toads daily, the population could still produce millions of new toads each season. The invasion front in Western Australia continues to advance at roughly 30 miles per year.
Researchers have therefore turned to a different approach for freshwater crocodiles, which are much smaller than saltwater crocodiles and pose little threat to humans. When cane toads reached the Kimberley, the results were severe. In Danggu Gorge, rangers found 60 dead freshwater crocodiles in 2019 and 63 more in 2020.
Instead of trying to make freshwater crocodiles resistant to the toxin, researchers focused on changing their behavior. The idea was to let a crocodile taste a cane toad once, become sick, and learn to avoid them in the future.
The work was done with Bunuba rangers, traditional owners of the land around the gorges. During the dry season, when water levels dropped and freshwater crocodiles gathered around remaining pools, rangers and researchers set bait stations near the water’s edge. Each bait was made from the hind leg of a cane toad, which contains much less toxin than the head. The leg was treated with a nausea-inducing chemical and suspended just above the water.
The crocodiles learned quickly. On the first night, most of the cane toad baits were eaten. Within a few days, the same crocodiles ignored the toad baits while still eating chicken placed alongside them. Nearly 2,400 baits were deployed across four gorge systems. After the program began, the number of dead crocodiles found dropped sharply.
For animals that spread across open bushland rather than concentrated water sources, researchers used a different method. The northern quoll, a small spotted marsupial about the size of a domestic cat, attacked cane toads and died in large numbers when the toads entered its range. In some areas, entire local populations disappeared.
Researchers made sausages from ground cane toad meat, excluding the most toxic parts, mixed with a nausea-inducing chemical. They dropped these sausages from helicopters across bushland before the cane toad front arrived. In trials with wild quolls, nearly two-thirds of animals that found the bait tried to eat it. Of those, between 40 and 68 percent developed an aversion to cane toads. They learned the lesson before real toads appeared.
Some native animals needed no training. In 2014, along a creek in the Kimberley, researchers began finding large cane toad carcasses on the bank each morning, up to five fresh bodies along a 16-foot stretch. Each toad had a precise cut through its belly. Camera footage identified the killer as the rakali, a native Australian water rat. The rat flipped the toad onto its back, slit open its belly, and ate the heart and liver, avoiding the skin and toxic glands entirely. It carefully set aside the gallbladder and targeted the largest toads, which carry the most toxin. This behavior appeared less than two years after cane toads arrived in the area.
Australian white ibis, sometimes called garbage chickens in cities, have been observed picking up cane toads and shaking them violently. The shaking stresses the toad and causes its glands to release toxin. The birds then carry the toads to a stream, wash them in the water, and swallow them. This behavior has been reported in several areas.
Other animals contribute pressure as well. Ants, water bugs, diving beetles, dragonfly larvae, and freshwater crayfish feed on cane toad eggs and tadpoles. Wolf spiders and huntsman spiders have been observed killing adult toads. The keelback snake, whose ancestors came from Asia where toxic frogs existed, tolerates cane toad toxins better than many Australian snakes and eats small and medium toads without dying. Red-bellied black snakes in areas with long-term cane toad exposure have become more resistant to the toxin, less willing to attack toads, and have developed relatively smaller heads that make it harder to swallow large toads carrying the most dangerous doses. These changes appeared in fewer than 23 generations.
At Fogg Dam, where toad numbers fell by 98 percent, researchers tracked 19 native species and did not observe an immediate recovery. The disappearance of the toads is only a first step, and ecosystems do not restore themselves quickly. Some damage is long-lasting. Goanna populations fell by 71 to 97 percent after the toads arrived, and many populations had not returned after 12 years. Two species were not recorded at all along more than 190 miles of surveyed river.
But the system is not static. When large goannas disappeared, some smaller species they had preyed on increased significantly, in one case by about 500 percent. Surviving predator populations now have a chance to breed with less toxic pressure, and the relationships between predators and prey may slowly rebuild.
Cane toads have not disappeared from Australia and may remain for a very long time. The conflict has changed, however. Saltwater crocodiles can turn cane toads into food. Freshwater crocodiles are learning to avoid them. Quolls are being trained before the toads arrive. Rakali surgically remove the toxic parts. Ibis wash the toxin away. Insects and spiders prey on eggs, tadpoles, and adult toads. Some snakes are evolving resistance in observable timeframes. People continue to trap toads, build barriers, collect eggs, and test new ways to protect native predators before the invasion front reaches them.
No single factor delivers a decisive blow, but together these pressures reduce the toad’s advantage. This does not mean Australia has won. The toads’ reproductive capacity remains enormous, and the ecological damage may persist for years. Some species may take decades to recover, and some may never fully return. The real question is no longer whether cane toads will disappear from Australia, but how much change native wildlife will undergo to coexist with them. The answer began to take shape with a small crocodile in the Daintree River that held a toxic toad in its jaws for 25 minutes and survived.
