Paracelsus' poison

Toad medicine

The Cane Toad. Young Bufo marinus

In an interesting conjunction of events, I brought home the DVD “Cane Toads; the Conquest” to show our Japanese exchange students something uniquely, if weirdly, Australian, on the weekend of Toad Day Out, when North Queenslanders compete to gather as many of the warty creatures as possible for mass extermination.

Growing up in Queensland, I understand the impulses that drive ordinary, kindly people into orgies of mass toadicide. It’s not just the sheer numbers of the things, making a walk to the outside loo somewhat perilous and coating kilometres of roads with lethal-skid inducing amphibians, it’s that they are toxic massacrers of wildlife.

Originally brought into North Queensland to control the cane beetle, they completely ignored their designated target, and promptly began eating great swaths of local insects and reproducing like mad. Predators of all things squamous and hoppy, including native lizards, the local marsupial carnivores and dogs soon found that the cane toad was not just another crunchy treat, but deadly poison.

Many frogs and toads secrete poisonous substances to discourage predators. After a mouthful of poison frog it’s a terminally stupid predator that will try eating them again. This may not do the chewed on frog or toad much good, but its relatives will prosper. Cane toads secrete a venom from the backs of their necks, it is so potent that dogs who drink from water bowls the toads have been sitting in can be poisoned. With the toad-induced carnage of native wildlife and pets you can see why people are infuriated by them.

The toads venom is a complex mix of chemicals. The most important is related to digoxin, the toxin found in the Foxglove plant, and works the same way. It changes the excitability of the heart muscle, causing the heart to contract wildly and ineffectually, or stop completely. In the spirit of my blogs namesake, we have harnessed these properties of digitalis in small doses to treat heart failure, where the heart does not beat strongly enough.

Toad venom has found its way into Traditional Chinese Medicine. Chan Su, amongst other things, is used as both a topical anaesthetic and an aphrodisiac. It is basically dried toad venom. Unsurprisingly, given the potency of toad venom and the variability of toxin levels in these preparations, there have been reports of severe toxicity and even death from using Chan Su.

Of course, lethality never stopped people in search of intoxication, In my youth, there were a fair few people who tried licking the toads, or smoking their dried skins, as a way of getting high. I’m surprised that more people weren’t killed this way.

With no effective predators in Australia the cane toads have marched relentlessly West and South, they are already in Kakadu, crossing supposedly impenetrable geographic barriers, and some scientists predict we will eventually see them in Adelaide. The parasitic lung worm that was a possible biological control agent doesn’t have seemed to paned out.

However, there might be one hope, paradoxically lizards that feed on the introduced toxic plant “mother of millions” are resistant to the toad toxins. So perhaps a crash breeding program of toxin resistant super lizards may stop the advance of the cane toad. That couldn’t possibly go wrong, could it?