June 1935, the cane toad began its invasion of Australia. Sailors brought the animal over from Hawaii in an attempt to control the cane beetle that was ravaging Australia’s sugar cane crops. It was a mistake that the continent’s wildlife would pay for. The toad did nothing to stop the beetles. Instead, it launched its own invasion, spreading across the continent from its north-eastern point of entry. As it marched, it left plummeting populations of native species in its wake.

The toads are born conquerors. Females can lay 35,000 eggs many times a year, and each can develop into a new frog in less than 10 weeks. They’re unfussy eaters and they’ll munch away on bird eggs, smaller native frogs and more. And they have large glands behind their heads, which secrete a milky poison. Local predators (or domestic pets) that try to eat them tend to die.

Now, Daniel Florance from the University of Sydney has found a clever way of corralling the cane toad invasion. He realised that humans have continued to give the toad a hand, long after we first brought them to Australia. By creating dams and troughs, we provided the toad with watery staging grounds that allowed it to spread across otherwise impassably dry land.

By blocking the toads from these hubs, we could prevent them from spreading over 857,000 square kilometres, an area of land the size of Pakistan. As Florance says, it’s not a “silver bullet for toad control”, but it can certainly help to cut the numbers of these troublesome trespassers.

Cane toads are less dependent on water than many other frogs, but they’re not adapted to truly dry climates. While some frogs burrow underground or create protective cocoons, cane toads simply lose water until they die of dehydration. In the heat of Australia’s dry season, they need bodies of water to survive. Fortunately for them, humans have provided them with moisture galore, in the form of cattle troughs, boreholes, and dams.

Florance fenced off these artificial water sources in the Northern Territory during the dry season, when temperatures can regularly climb as high as 37 degrees Celsius. He used wire and metal posts to prevent the toads from jumping over, and buried cloth to prevent them from digging under. Once the barriers were set up, Florance evicted all the toads within them, more than 2,000 in total.

The fences worked. In the following months, Florance couldn’t find any toads within the protected areas (although he found several that died at the fences, trying to get in). He fitted radio-trackers to 60 individuals and followed them in their quest for water. Near the fenced areas, all of these toads died within three days. Most of them kicked the bucket after just twelve hours, and they had lost around half of their body weight by that point. Meanwhile, almost all of those released near unfenced water survived.