Australia's cane toads are an instructive case of the problems of invasive species, as the creatures were originally introduced to control pests and then became a pest themselves. But now new research indicates that the best control mechanism is surprisingly simple: fences.
Cane toads were introduced in Australia in the 1930s to deal with pests that were attacking crops. Of course, cane toads also eat anything they can fit there mouths around. Including a ping pong ball bouncing past them:
They're also poisonous, and Australia doesn't have any predators who can take them out. To deal with this self-inflicted toad invasion, the country has tried a bunch of things, including culling the population.
A team of researchers has recently published the results of a study in the Journal of Applied Ecology, where erecting fences around water sources proved very effective in eradicating the hopping menace. Since water storage provide a lure for toads looking to escape the heat, researchers erected fences out of cloth around three dams in the Victoria River region. They monitored the set-up for a year and discovered that the cane toads couldn't get around the fences and died in large numbers trying to get to the water. Explained lead author University of New South Wales Associate Professor Mike Letnic:
The toads were still attracted to the water but they died en masse while attempting to settle at the fenced dams.
Their numbers remained suppressed for a further year. By comparison, there were 10 to 100 times more toads living at the unfenced dams that were used as controls in the study.
The study further points out that they cane toads could be controlled by removing water collection areas in large swaths of land, so that the toads would perish before finding water. However, says the study, that's not something that is as feasible as fencing:
If control of cane toads was the sole objective of land managers, complete removal of dams and hence invasion hubs would eliminate toad populations from areas that are naturally waterless during dry seasons. However, because the landscapes of northern Australia are managed primarily for the purpose of cattle grazing, the removal of dams is unlikely to be a tenable strategy. A more realistic strategy for cane toad management in pastoral landscapes would be for wildlife agencies to work with pastoral land managers and manipulate existing dams so that they can no longer function as invasion hubs for toads. This could be done by replacing earthen dams with plastic or steel tanks (Fig. 1d), which do not allow toads to access water, yet still provide water to livestock via troughs. Another potential advantage of using tanks as reservoirs at AWP instead of dams is that tanks tend to have lower losses of water from evaporation and seepage than dams. Consequently, many pastoral managers are of the opinion that once established, tanks cost less to operate than dams, because less fuel is required to maintain reservoir levels in tanks.
Although it is a conceptually appealing idea, replacing earthen dams with tanks would be a difficult strategy to implement because of the considerable effort and cost required to decommission dams and install a large a number of tanks. Furthermore, tanks must be maintained so that they do not leak, as even small leaks from tanks can sustain toads. Converting dams into ecological traps by establishing permanent water exclusion fencing against toads, as we have demonstrated in this study, is a comparatively low-cost method
After decades of fighting this problem, it may be as simple as fencing off water.