Myth Busting Monday: Cane Toads
You don’t have to be an expert in Zoology to understand that cane toads are a serious threat to biodiversity in Australia. It has garnered enough media attention to render it a permanent dirty word in our national vocabulary. Along with it has come a really negative attitude towards the toads, part of which results in sensationalised tales and urban myths. So I thought for this Monday’s instalment of myth busting, I’d depart from historical myths to a Zoological one.
Myth 1: Touching a cane toad will make you sick or kill you
It is indeed true that cane toads secrete a bufotoxin from parotoid glands around their shoulders. However, it cannot be strategically excreted by the cane toad in any way, shape or form. The toxin is only excreted by force, i.e., squeezing the glands, or by vigorous trauma/shaking. This is why dogs are so much at risk from the bufotoxin, as they will often pick up and shake the toads. In fact, due to its semi-permeable skin, the cane toad is at more danger from being held by you than you are from it. I have handled cane toads in prac many times before, in one case where we expressed the toxin deliberately, and I am still alive. Amazing. The only way you can come to harm is if you ingest the toxin, get it your eye or in an open wound. The toxin is highly water soluble, so it washes away easily. Though there is no guard against stupidity. If you ingest the toxin, you will become ill. The same goes for the eggs. I know, who would eat the eggs, right? Anyone who did the Vertebrate Structure and Function class with David will know all about the guy who, in an effort to impress a female classmate during a toad dissection class, ingested the entire compliment of eggs discovered in the body cavity. He had four cardiac arrests before he made it to hospital.
Myth 2: The toad-eating frog is here to save the day!
The story about the Dahl’s Aquatic Frog gained a lot of publicity recently. The papers championed this native frog that could eat cane toads and hence control their numbers. Turns out this frog is just like all the other natives: quick to die and quicker to learn not to go anywhere near the cane toad.
Myth 3: Cane toads can change their gender.
They can’t. This myth seems to have arisen from a perceived lack of sexual dimorphism early on.
Myth 4: Cane toads have no natural predators
In reality, there are so many natural predators of the cane toad that it is estimated that only every 1 in 10,000 tadpoles survive to adulthood. Saw-shelled turtles, keelback snakes, wolf spiders, freshwater crayfish and dragonfly nymphs are just some of the examples of cane toad predators. As an adult, the number of predators decreases, but the keelback snake is one of them.
Myth 5: Cane toads don’t even eat cane beetles.
Cane toads do eat cane beetles. However, the environment in Australia differed substantially from that of Puerto Rico in which the cane toad worked successfully as a beetle control (ironically, it was introduced there to control rodents). The cane fields themselves offered no protection from predation during the day. Outside the plantations, however, the cane toad found an almost limitless boundary of food and habitat, and so the cane toad rapidly moved away from the plantations and into more the luxurious environments Australia had to offer.
Myth 6: The people who released the cane toad were ignorant
Contrary to popular belief, there was a lot of good science behind the release of the cane toad that raised concerns about the environmental impacts. The release of the cane toads was even halted at one point due to this. But as is a common theme, money > nature. The cane beetle was threatening agricultural yield. Money talks. Political pressure to solve this issue took precedent, and so the cane toad was released. You know how that story ends.
Myth 7: The cane toad will spread all over Australia.
A lot of early predictive modelling showed the distribution of the cane toad to be much greater than what we currently know. A lot of work has gone into this (as any of Mike Kearney’s students will know from tales of his research), combining the actual physiology of the cane toad with climate models. We know that the cane toad cannot exist in environments less than 5°C, so that pretty much rules out most of southern Australia.
Myth 8: We can control cane toads by catching them and killing them.
I’m sure you’ve seen all the well-meaning toad control groups that go out in their numbers to catch the toads. Unfortunately, it is all to no avail. The only way to eradicate a species by this means is to remove them beyond a rate at which they can reproduce. This works well for species with a long gestation (e.g., horse, camel, etc), but not for toads. A female can produce 30,000 eggs in just one clutch, and a single one of those eggs can yield a mature toad in just a few months. Miss just a few toads and the number will bounce back just as quickly. In fact, as you have just removed all their competitors, it makes it that much easier for those left to survive. Despite all the hard work that goes into it, population surveys have revealed that the rate of expansion of the toads is just as fast as before any control measures were taken.
Myth 9: It is okay to kill cane toads inhumanely.
This is perhaps the most hurtful myth of all, and one I have been subjected to personal attack many times for combating. This surprised me at first, but once you understand the power of an idea that has been so firmly embedded, it becomes less and less so. There is this idea in society that because they are introduced, harmful species, it is okay to kill them by whatever means necessary. It’s not. The fact is, it is not their fault they are here. It is ours. Yet this behaviour persists due to nothing but the fact that we are speciesist. It is quite okay to club a cane toad to death with a golf club. What about a horse? A cat? A fox? A rabbit? What about the worst invasive species of all – homo sapiens? A poll on the Sunshine Report Daily‘s website showed that 60% of people still prefer to kill toads with a golf club. The argument for cruelly killing toads is often that one is helping the environment by doing so. As seen above, it’s not. Individual acts of cruelty do nothing but bring suffering to an animal that has no choice as to its circumstances. If someone feels that strongly about removing the toad, there are 3 ways it can be killed humanely:
1. Blunt force trauma. This should only be done by someone who is an expert in it and can render death with a single blow. Most people, however, are not, and will repeatedly beat into the toad until it is dead.
2. Anaesthetic overdose. This is what is used in the lab, but is largely unavailable to the general public.
3. Refrigeration. As mentioned before, a toad cannot survive below 5°C. The most humane way available to the general public is to pop them in a container (to avoid contact with any cold surfaces) and put it in the refrigerator (set at at least 4°C) – the cane toad’s metabolism will slow down. It will begin to feel sleepy and become unconscious. It should be left for at least 24 hours, before finally being put in the freezer: ice crystals will form in the cells, perforating the walls and render the toad dead. If that is not fast enough for some (as some do argue that no one can be bothered waiting that long), Benzocaine can be used to render the toad unconscious within 30 minutes, after which time it can also be frozen.
This animated video gives a comical (and potentially offensive, so don’t click if you’re opposed to blood, guts and the occasional spot of bad language) look at the attitudes that have developed in response to cane toads.
Myth 10: You decide!
There are so many more cane toad myths I haven’t even brought up today. So what crazy toad stories have you heard? Is there anything you’ve been told and have always wondered if it was or wasn’t true? Something you thought was a fact the perhaps you now question?