The story of the cane toad is a story every good ecologist can recite from the top of their heads, popularized by the documentary Cane Toads: an Unnatural History. It is a prime example of species introductions gone horribly wrong.
First thing’s first, what’s the difference between an introduced species and an invasive species like the cane toad? First, a native species is a species that occurs naturally in an area1. An introduced species is a non-native species occurs outside of its natural range caused by human activities, whether its on purpose or accident. There is a lot of debate over whether what period of time can an introduced species that has adapted well can be called native, but that’s for another time2. An introduced species becomes an invasive species when it spreads to a degree that causes damages to the environment, economy, human health or some combination of the three3.
Now that the boring vocabulary lesson is out of the way, what is the story with the cane toad?
Photo by Jodi Rowley.
The cane toad (Rhinella marina) was introduced to northeast Australia in the 1930’s from the Americas with the idea of feeding on the destructive sugar cane beetle population4. However, the toads were unsuccessful at controlling the cane beetle population because the fields offered “insufficient shelter for the predators during the day” and because the beetles resided at the top of the sugar cane which are inaccessible to the toads5.
Moving forward, the cane toads ate most everything (including pet food) except the cane beetles, devastating flora and fauna food resources for native species. In addition to their generalist diet, lack of predators attributed to its toxic skin and quick breeding, the cane toad population exploded in Australia, now with more than 200 million toads4.
The spread of cane toads from 1940 to 1980 (by Froggydarb)
With the population so high and the damage its causing, the cane toad is now considered a pest in Australia and population control methods are being tried and tested. Methods such as trapping, reproductive control6 and humane culling7 have been largely unsuccessful. There is even a bounty on the toad population with events such as Toad Day Out, where toads are caught alive with prizes for the catcher of the heaviest toads before the toads are… taken care of8.
The cane toad is one of the most studied introduced species and is considered one of the most important lessons of species introductions9. It is a cautionary tale that regardless of how much we think we know about these animals and their life histories, they can always surprise us and at the end of the day, humans are not above nature.
Bonus fun facts
- The cane toad is the world’s largest toad10.
- The cane toad situation is referenced several episodes of The Simpsons, including “Bart vs. Australia”, “Whacking Day” and “Bart the Mother”
Notes and sources
1 European Union (1979) Convention on the conservation of European wildlife and natural habitats (Bern Convention). 19.IX.1979. The Council of Europe, Bern, Germany.
2 The honey bee was introduced to the U.S. in the 1600’s, but we don’t really think of it as non-native because it’s been here so long (Garvey, 2008).
3 Joan G. Ehrenfeld (2010), “Ecosystem Consequences of Biological Invasions”, Annual Review of Ecology, Evolution, and Systematics, 41: 59–80
5 Tyler, Michael J. (1976). Frogs. William Collins (Australia).
7 “Methods for the field euthanasia of cane toads”. Australian Government, Department of the Environment and Energy. 2011.
8 Penny Timms (25 March 2011). “Residents declare war on cane toads”. ABC News Online. Australian Broadcasting Corporation. Retrieved 11 April 2011.
9 Easteal, Simon (1981). “The history of introductions of Bufo marinus (Amphibia : Anura); a natural experiment in evolution”. Biological Journal of the Linnean Society. 16 (16): 93–113
Photo by Chris Ison.