Toad-ally Taking Over

Did you ever wish you had a superpower? Maybe you wished you could fly? Or had super strength? Or could shapeshift?

Well, the cane toad has a pretty incredible power. It emits a milky, white poison from glands behind each of its shoulders. One lick or bite of the toad causes animals’ hearts to beat rapidly, uncontrollable shaking, and even death — a poison-induced heart attack. People have reported seeing birds, which sunk their beaks into a toad, fall dead out of the sky.

But the cane toad’s superpower — or defense mechanism in biological terms — has wreaked havoc in northern Australia. Brought to Australia to kill agricultural pests, cane toads spread uncontrollably and quickly became the pest.

Invasive Species

An invasive species is a species that is not indigenous (or native) to a place. Invasive species share common traits: they reproduce quickly, adapt rapidly to their new home, and cause serious damage. Cane toads check all of the boxes and hold the title of one of the 100 worst invasive species in the world, according to the Global Invasive Species Database. 

The squat, warty toad is native to Central and South America. But they made their debut in northern Australia in 1935. The Australian government brought cane toads to Queensland to eat beetles that destroyed sugar cane crops. Unfortunately, the beetles lived on the upper leaves of sugar cane plants, and cane toads could not jump or climb high enough to reach the beetles. The effort was a major failure! 

Although cane toads were poor beetle exterminators, they were excellent at multiplying. In the 1930s, the government released 2,400 cane toads in Queensland. Now scientists estimate more than 200 million toads live in Australia, according to the World Wildlife Fund (WWF). Each year, cane toad populations grow and hop westward across the continent. Toads have invaded more than 386,000 square miles of Australia, an area greater than Texas and Oklahoma combined, cites Life Science.

How Cane Toads Invade

Remember the characteristics of invasive species? Let’s look at how the cane toad reproduces quickly, adapts rapidly, and causes severe damage. First, cane toads breed constantly and lay strings of eggs, each containing between 8,000 and 30,000 soon-to-be toads. Each tadpole quickly develops into a warty invader in less than ten weeks. And cane toad eggs, hatchlings, and tadpoles are all poisonous, so even tiny toads can kill. 

Second, cane toads are hardy and quickly adapt to new environments. They can survive in towns, fields, sandy dunes, grasslands, rainforests, and swamps. Cane toads need a slightly moist home but can find water in unusual places like dew, moist soil, and even animal poop. They absorb water through their skin and store water by ballooning their body to survive dry spells. Also, cane toads eat almost anything. Their Australian home is like an all-you-can-eat buffet. They feast on insects (except the beetle they were meant to kill), amphibians, animal carcasses, rodents, small birds, and even their own babies. Scientists found that tadpoles will devour smaller, younger cane toad hatchlings. 

Furthermore, cane toads have no natural predators in Australia to control their numbers. In their native habitat, predators developed immunity to the toad’s poison and could eat the toads without fearing death. But larger predators in Australia — lizards, crocodiles, turtles, snakes, and dingoes — have no resistance to the poison and fall victim to its heart-seizing effects. 

Finally, as they advance westward across Australia, cane toads have destroyed Australia’s biodiversity. Scientists estimate a 70-90% decline in predator species when cane toads marched into a habitat, according to evolutionary biologist Rick Shine. For example, leading toad expert Graeme Sawyer noted the disappearance of the goanna, a giant monitor lizard, and a decrease in pythons in Kakadu National Park, a biodiverse nature reserve in the Northern Territory.

Battling the Cane Toad

Desperate times call for desperate measures. With millions of cane toads in northern Australia, people are testing wild ideas to control their spread. In one effort, the Cane Toad Coalition fed predators sausages laced with cane toad poison. The predators got momentarily sick — kind of like food poisoning — but built up immunity to the toad’s toxin and learned to avoid eating adult toads which are the most powerful poisoners.

Researcher Daniel Florane experimented with fencing off cane toads from water. According to Florane, humans helped cane toads multiply by building canals in northern Australia. Unfortunately, these man-made waterways gave toads the moist environment that they needed to thrive. So he built fences around the canals so the toads cannot access them. As a result, the cane toads dried up and died. 

And it gets wilder — evolutionary biologist Rick Shine pits meat ants against cane toads. Meat ants are aggressive and, most importantly, immune to the cane toad poison. The ants work together to attack cane toads. During early experiments, he reported that 50% of toads died immediately after being attacked, while 88% died within 24 hours from injuries. And best of all, meat ants are native to Australia. So past mistakes — like introducing foreign toads to kill beetles — will not be repeated in the battle to control the cane toad.