The Most-Traveled Cane Toad

The Many Homes of the Cane Toad

The following questions are answered on this page.  Either click on the following bookmarks, or just read down the page!

How or why is the cane toad outside of its native habitat?

What characterizes cane toad habitat? 

What effect have humans had on toad habitat? 

Where is the native habitat for the cane toad?  

Where all does the cane toad now call home? 

 

How or why is the cane toad outside of its native habitat?  The migration of the cane toad is a long story, and while the toad is very adaptive, it could not have accomplished its feats without humans!  So, let us begin our story with why humans first thought that they loved the cane toad.  Back in 1930, sugar cane was the main export of Australia, and hence was very important to the economy.  However, Australia had a problem: beetles (Greyback beetles Dermolepida albohirtum and Frenchi beetles Lepidiota frenchi) were destroying the sugar cane crops.  Here are those beetles.       

Australians learned of the cane toad in 1932 when a sugar technology conference was held in Puerto Rico.  There, Australians learned of Bufo marinus, a giant toad with a giant appetite that just might gulp up every pesky cane beetle in Australia – after all, the toad seemed to have solved beetle problems in Barbados, Jamaica, and Puerto Rico.  In fact, when the toads had been imported to Puerto Rico, the toads had not only removed insects but rats – or so the situation appeared.   Hence, at the Puerto Rican sugar conference, the toads were touted as a successful intervention for crop pests.  

(In hindsight, scientists aren’t sure that the toads had any effect on the insects or rats – the appearance of the toads and the relative disappearance of the pests may have just been a big coincidence.  But anyway...)

Because sugar cane was so vital to the Australian economy, there was huge social pressure on the Australian government to “do something” about the beetle problem.  With so much pressure, the government quickly decided to import the promising cane toad. 

In 1935, 101 toads arrived alive in Australia, where an eager scientist met their every desire, even encouraging their reproduction with a pond featuring a water fountain.  The climate and habitat was ideally similar to the cane toads’ native habitat, and so the toads thrived.  One person even said, “we’ve got these bloody grubs by the balls”…but that wasn’t to be true, because it would turn out that toads would have humans “by the balls”. 

The toads were initially released in 9 locations.  Unfortunately, the toads didn’t like Australian cane fields.  The fields were too dry and sunny for these moisture-loving toads, and the intended food for the cane toads were too high up in the plants for the toads to encounter the bugs in any quantity.  All the toads might find were the beetle larva (pictured).  Furthermore, toads are mostly active at night, whereas beetles prefer daytime activity). The only “thing” the toads received out of the cane fields was the cane toad name.  Ever adaptive, however, the toads moved out of the failed cropland habitat and into the rest of Australia, both wild and civilized.  Today there are over 200 million toads in Australia!  Let’s take these two habitat types separately.

In the wild, cane toads prefer grasslands to dense forests, in which their big bodies and short legs make navigation more of a challenge.  Regardless, they found plenty of food…insects, other frogs, small rodents, small birds, snails, small snakes, and pretty much anything else that would fit into their mouths!  Because they have poison glands behind their ears, few creatures could eat them and live to brag about it…none of the creatures which might eat them (snakes, birds, monitors, crocodiles, wild cats and dogs) had evolved to deal with toad toxins, because they hadn't been exposed to toads. 

Put it this way: it takes time for species to evolve the ability to survive much less easily tolerate a poison, and when a toxin (or cane toad) suddenly appears, that evolution has not had time to occur.  The result is that this toxic toad has no real enemies in this non-native habitat…the few creatures that dare even attempt to eat it often die. 

So, the cane toad has plenty of food and no enemies.  Any guess what this means?  It is the perfect storm for a population explosion: cane toads everywhere.  They out-eat their smaller competitors, then they out-breed them too (how can any amphibian produce more offspring than the cane toad, when one female cane toad can lay 30,000 eggs in one batch, and the toads grow into mature adults faster than those of native species?).  And so, entire species collapse --either from being eaten by the cane toad, or starved due to the cane toad’s voracious appetite, or its eggs and offspring outdone by the cane toad-- and eventually the altered species populations effect the entire ecosystem.  And, the toads can spread at up to 17-31 mi (27-50 km) each year in the most favorable of habitats.  In some locations, there are 5000 toads per acre.  They are taking over Australia.

On to a somewhat nicer topic, consider the cane toad in the human environment.  Humans provide the habitats that these cane toads loved: humans clear dense forest in favor of grasslands, parks, and cities.  Human habitats (cities) often provide the cushy life for toads:  there’s shade, water, and the light.  Light?  Well, the cane toads don’t care directly about the light, but about the concentrated bug populations that swarm lights.  Its as if, instead of having to scavenge for food, the cane toads need only appear at the dining room table – all courtesy of humans.  There are also humans that like the toads and thus intentionally feed them.  Cane toads are even known to eat cat and dog food, and to learn and then appear at the scheduled feeding times.  Cane toads must think that humans love them…providing the easy life.                 

                                                                                                                                                             Cane toads must think that humans love them…providing the easy life.  Yet in reality, there are many people that dislike them.  Some people will intentionally swerve back and forth across a road, trying to kill as many cane toads as possible.  This is almost a sport to people, as not only does it reduce the numbers of what has become a nuisance species, but the toads make a popping sound as they explode when hit.  There are also government programs aimed at reducing-and hopefully but unrealistically eradicating- the cane toad population.  (See Anuran Populations for more on population control efforts).

The native range of cane toads includes the huge swath of land from Rio Grande Valley, Texas, through Central America and Archipelago islands and including the upper half of South America.  Within this area, it does exist at high altitudes (apparently due to thermal limitations), and thus stays out of the Mexican plateau and sierras.  It occurs on both sides of the Andes, but the species has genetically separated somewhat in a group on each side of the Andes.  Its southern boundary is essentially a diagonal line through Peru, Boliva, Paraguay, a tiny tip of Argentina, and including the vast majority of Brazil.  It prefers lowlands, existing up to 100m elevation above sea level.  Fossil records of this old species indicate that it has always preferred grassland to forest habitat.

Due to mostly intentional human transport, today cane toad exist in over 50 countries or territories.  Humans have introduced the cane toad to the following: Japan, Philippines, Taiwan, Thailand, Egypt, Mauritius, Bermuda, US (Hawaii (5 islands), Florida, Louisiana), Antigua, Barbados, Cuba, Dominican Republic, Grand Cayman, Grenada, Hispaniola, Haiti, Jamaica, Martinique, Puerto Rico, US Virgin Islands, British Virgin Islands, Australia, Papua New Guinea, American Samoa, Fiji Islands, Solomon Islands.  No doubt about it, this toad has more stamps on its passport than due most people! 

Humans introduced cane toads to many areas in an attempt to control pests, primarily insects such as those that destroy sugar cane crops.  It is from its attempted sugar cane application that its common name of “cane toad” is derived.  The toad likes to live near fresh water.  Their scientific name, Bufo marinus, translates to “marine toad,” but they aren’t marine (although tadpoles can tolerate brackish, or partially salty, water).  They require freshwater, even when they live along coastlines. 

                                      

                                                        Well, it sure looks innocent!         

Now, learn what the cane toad eats!