The cane toad is an infamous example of biological control gone wrong but what exactly is the problem and why can’t we fix it?
The cane toad (Rhinella marina) is a large, terrestrial toad native to Central and South America. It was introduced to Australia by the sugar cane industry in 1935 in an attempt to control beetles that were damaging the sugar cane. This was done against the recommendations of many scientists at the time and was proven to have been exceedingly ill-judged.
Thousands of toads were released without any scientific testing on the breadth of their diet, and they not only failed to control the beetle, but turned their carnivorous attention to any creature that was small enough to be swallowed – becoming a significant problem themselves. Without their own natural enemies and thanks to some formidable defences, they were able to spread rapidly.
The toads caused a complete depletion of many species and also caused the poisoning of many humans and their pets. The toads possess a gland behind their ears, able to secret a milky liquid poison in defence to predation, however, the toxin proved to be dangerous to many species, causing malfunction of the heart (it’s unlikely to be fatal in humans).
Although it was carried out in the name of biological control, today’s practitioners consider this release to have been a highly irresponsible act. With today’s stringent regulation and extensive scientific testing, the introduction of the cane toad would not be allowed.
There have been various attempts to reduce the cane toad population. Trappings were largely unsuccessful as they were time consuming and accidentally trapped native species, such as frogs and bluetongue lizards. Introducing a viral or bacterial pest has also been considered but the idea was soon dismissed – fighting an out-of-control invasive species with another non-native species has the potential to go very wrong, as all of the bacterial and viral agents proposed could negatively impact native species as well as the cane toad. It’s important to note that although people are keen to reduce the number of cane toads, there are guidelines for doing so and the RSPCA has produced a list of inhumane ways that should be avoided at all costs, most of which are illegal anyway.
Societal values have also changed; we now value native species’ biodiversity far more highly than perhaps ever before. In fact, biological control today is often used to increase species biodiversity.
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Photographs: Brian Gratwicke
Image from www.flickr.com/photos/stuutje