Cane Toads: a Toxic Relationship with Australian Fauna
Ahh the cane toad, a name that strikes horror in the hearts of Northern Queensland locals and environmentalists alike. This pest species has been a troublesome addition to the Australian landscape, causing the dramatic decline of several native species. Many share the general feelings of distaste for these annoying amphibians, but how did this invasive species arrive in Australia in the first place? And what’s all the fuss really about?
A Horrible History
Local to South and Central America, cane toads (Rhinella marina) were thought to be the miraculous answer to an economic crisis in the sugar cane industry. Many believed that the cane toad was the perfect biological control against agricultural pests (namely beetles) ravaging through plantations.
After hearing of the cane toad’s great success in reducing beetle populations in Puerto Rico in the early 20th century, Australia’s interest was piqued. After all, Australia had already seen just how effective biological controls can be, having introduced Cactoblastis cactorum, a moth native to Argentina, to prey upon the wildly out of control prickly-pear cactus, a resounding victory. In short, using biological controls was very on-trend at this point in history.
In 1935, 102 toads were delivered from Hawaii to Far North Queensland, where they were bred in captivity. Two months later, 2,400 were released into the cane fields. With the toads on the loose, it was only a matter of time before the beetle crisis was a thing of the past… or so the would-be saviours of the plantations thought.
The only trouble: they were terrible at their job! The cane toads were released to target greyback cane beetles. However, in hindsight, this was a poor solution for a couple of reasons. Let’s count those reasons, shall we?
- Greyback cane beetles feed in the top canopy of the sugar cane stalks, while cane toads tend to dwell on the ground below, not particularly known for their climbing or flying abilities.
- Greyback beetles are typically diurnal, meaning they like to be out and about during the day, whilst Cane toads are nocturnal, active at night.
These two species seem to have very different ecological niches; they were just never supposed to meet!
The Situation Toaday
Fast-forward 83 years: Cane toads have spread approximately 1 million km2 across parts of Queensland, New South Wales, and the Northern Territory, continuing their invasion West at approximately 40-60 km per year. From those 2,400 toads released back in the thirties, there is now a whopping 200 million! Yes, you read that right! It is safe to say they have well and truly settled in here in Australia. So why is this an issue again?
A Worthy Competitor
Firstly, these guys are incredible generalists; they aren’t fussy at all. They can occupy a HUGE range of habitat types as seen from their wide distribution, as long as they have enough moisture to keep themselves happy.
In addition to their habitat adaptability, cane toads will eat pretty much ANYTHING (as long as it can fit in their mouths). From other amphibians and tadpoles, to reptiles, small mammals, snails, insects, and even human food! Many pet owners have also caught toads red-handed stealing their pets’ food! Sadly, many native (and sometimes threatened) species become the cane toad’s dinner – toads just don’t seem to be as concerned about protecting endangered species as we are!
The generalistic nature of their lifestyle means cane toads are fierce competitors in the wild, out-competing many native species for food and breeding sites. Speaking of breeding, the females can lay up to 30,000 eggs in one brood, leaving native frogs wanting. Try out-competing that!
Oh, and did I mention that they’re poisonous? These tough toads produce poison not only in their adult form, but across the entire lifespan; from egg to tadpole to toadlet to fully fledged adult toad. Adults exude their bufo toxins from glands on their shoulders when threatened, so that any hopeful predators quickly learn not to mess with this toad. These toxins are a death sentence for many native animals, acting on cardiac tissue and the nervous system, causing paralysis and death.
Hope is on the way!
Happily, there is new research surfacing, indicating that many animals are now adapting to having cane toads as their neighbours. Some are learning not to eat them, others have learned to flip them over and only eat their bellies, avoiding the poison glands. One study has discovered a correlation between snakes that are vulnerable to cane toads, and a reduction in gape size. This phenomenon has been suggested to be a result of natural selection favouring snakes that don’t have large enough mouths to swallow these poisonous pests.
Thankfully, many ecologists are concentrating their efforts on controlling the cane toad situation in Australia, mapping future distributions and forming plans of attack. But that doesn’t mean the cause doesn’t need more help! If you want to take part in citizen surveillance next time you find yourself up north, you can map your toad spottings on ToadScan, a sub-program of FeralScan, an organisation backed by the NSW government to combine government, research and community efforts to addressing Australia’s pest issues. This resource also has some great information on how to spot a cane toad and more about their fascinating biology.
Better hop to it!