display | more...
Cane Toads - Bufo marinus

Description and Distribution

Cane Toads are very large and heavily built amphibians (up to 15 cm long) with warty skin. Females tend to be larger and smoother-skinned than males. They are olive-brown to reddish-brown on top, with a paler white or yellowish belly. The underside is usually flecked with brown.
Their most distinctive features are bony ridges over each eye and a pair of enlarged glands, one on each shoulder. These glands ooze Cane Toad venom.
The call of the male Toad is a high-pitched "brrrr" which sounds like a telephone dial tone.
They were introduced to Australia in 1935 at Gordonvale, North Queensland. Since then they have expanded their range to include about half of Queensland. They have spread to the Northern Territory and New South Wales, and there are fears that they may soon colonise areas of the Kakadu National Park. Occasionally individuals have shown up as far south as Sydney. It appears that these have been carried south, in plants for example, and there is no evidence of a breeding population here.

Diet

Like all frogs, they are primarily insect feeders. However, they will attack anything that moves and is small enough to fit in their mouths. Their diet includes small lizards, frogs, mice and even younger Cane Toads. They have also been known to steal food from dog and cat bowls.

Behavior and Breeding

They are highly adaptable, both in terms of survival and reproduction. They are much more tolerant than other Australian frogs of variations in water salt content, and can survive and breed in brackish water.
Because their diet is so variable, they don't need to expend much energy searching for food. They can just sit in a convenient spot, and gobble up anything that wanders by. In urban areas, they are often seen gathered around street lights eating insects attracted by the light.
They need only a small pool of water for breeding. A female toad can produce vast quantities of eggs, up to thirty thousand a month. The males fertilise the eggs as they are laid in long strands. Males will attempt to mate with anything resembling a female toad - living or dead.
In three days the eggs hatch into small (3 cm) jet black tadpoles - unlike those of any native frog. These tadpoles become toadlets unusually early, so they are out of the water and hopping around faster than most other frogs.

Cane Toad Venom

One of the most important factors in the success of the Cane Toad is that they are highly poisonous to eat, at every stage of their life cycle.
All frogs and toads may have enlarged chemical-secreting glands at particular points on their bodies, of small glands spread over the whole skin. The chemicals they produce are highly varied, and in some cases may be highly toxic. The Cane Toad is one such amphibian. A Cane Toad's reaction to a threat is to turn side-on to its attacker so that the venom glands face them. Cane Toad venom is also found all over their skin. Animals picking up a Cane Toad and receiving a dose of venom may die within fifteen minutes.
The glands on the Cane Toads' shoulders are also capable of oozing venom or even squirting it over a distance of up to 2m if the toad is particularly roughly treated. The biggest danger to humans is that the venom could come in contact with the eyes, where it causes intense pain and temporary blindness.
If handling a Cane Toad, it is important to wash your hands immediately afterwards and to be careful not to touch your eyes. If any venom does affect the eyes, bathing in running water will relieve the pain. Never eat a Cane Toad, its eggs or its tadpoles.

Ecology

There is still much work to be done to fully understand what effects Cane Toads have on native wildlife, and just how far they can spread. There are some reasons for optimism. In the areas where Cane Toads have been around for the longest time, their populations have declined after the initial population explosion. It is also possible that some native animals are learning to avoid eating them. Other animals have shown they can eat the toad. The Keelback Snake can detoxify the venom and Water Rats, Ibis, Crows and some other birds turn the toads over and eat only the non-poisonous internal organs.

These fun little critters are the subject of a documentary which clearly ranks among the five oddest things I've ever seen, and may very well be right at the top (though there's always Being John Malkovich for competition). The documentary, Cane Toads, was produced by Australians, and, associated with Australian sense of humor, produced in me, an American, more of a feeling of dislocation and wonder at the oddness of things than a desire to laugh out loud. They say that humor results from the release of nervous tension; this seemed to play with that intuition by continuing to build it throughout--it was like a joke without a punchline, but which describes something so odd it's as though there's almost an attempt to subtly imply a punchline. The problem is, there are so many weird things going on, it's hard to tell which of them should be the focus of such a denouement. Some examples:

  • There's a guy who talks about how he has developed an addiction to smoking an extract from the poisonous toads. Funky on its own, but when he tells the interviewer that the first several times he tried it, he became violently ill, the viewer is left with no choice but to write off humanity as an evolutionary dead end.
  • A little girl, about five years old, plays with these toads as though they were a cross between pets and dolls. Apparently quite docile, they submit to being cradled, sat at tea parties, and even DRESSED UP IN DOLL'S CLOTHES. It's important to understand, these things get huge--we're talking Chucky-sized, here, not some wimpy little Barbie-magnitude things.
  • One guy, who works with animals, hates the toads. Not exceptional in itself, but when he talks repeatedly and with strong feeling and gruesome detail about how horrible they are, because one of his more predatory charges ate one and died, the oddity of this man's obsession sets in.

I can't really describe it, and I'm not entirely sure I recommend it, but it's awfully surreal.

Physical Characteristics:
The cane toad, or bufo marinus, is a rather heavily built and ugly amphibian. The skin on its dorsal region is a shade of brown, which, depending on each toad, can range from olive-brown to reddish-brown. The skin on the ventral area can be a shade from white through to yellow and is often speckled with brown spots. The skin is leathery and covered in brown warts, with male toads usually being more coated in the warts than females.

Two of the most distinctive features of the cane toad are its paratoid glands and the dinstinct bony ridges that extend over each eye. The prominent paratoid glands are positioned behind the ears and extend to around halfway down the back. The glands will release a milky bufotoxin (which is basically a poisonous venom) when the animal feels threatened. The toxin can cause vomitting, twitching, shallow breathing, short-term paralysis and may be lethal to its predators. This toxin is also quite capable of killing humans.

The hands and feet of the cane toad are small. Between the toes there are leathery webbing however this webbing is missing between the fingers. Because of its small hands and feet and relatively large body, the cane toad takes short, speedy hops. Their structure makes it unable for them to make high leaps, thus these amphibians only live on the ground.

Cane toads can grow up to 20 centimetres and can live up to 20 years.

Habitat:
Cane toads are usually found in wet and seasonally dry tropics or in warm temperate to semi-arid climates. They can, however, easily adapt to other environments, able to survive in a temperature range of 0 degrees Celsius to 41 degrees Celsius. Providing that an area has a decent supply of water for breeding, suitable temperatures, shelter and a sufficient food supply, cane toads will survive.

Distribution:
Cane toads are the most commonly introduced species of amphibian in the world. Although they have been introduced to Hawaii, Puerto Rico, Florida, American Samoa, the Virgin Islands and Guam, its notoriety is more commonly thought of in Australia. Cane toad infestation in Queensland is so bad, population density is some ten times more than it is in its native home of Venezuela.

Cane toads were first introduced in Gordonvale, a town near Cairns. Over the past 67 years the cane toad has spread across a significant portion of Australia. Their range stretches from the north eastern half of Queensland, northern New South Wales and the Northern Territory. Cane toads are also capable of inhabiting Western Australia, but this hopefully won't happen (if it does) for years.

Introduction:
The toads were initially introduced into the country by the Australian Bureau of Sugar Experiments Station in Gordonvale 1935. More were later released around Cairns and Innisfail. Initially, 3400 toads were released in hope they would control the infestation of greyback and frenchie beetles, whose larvae was causing serious damage to Queensland's sugar cane industry. The beetles couldn't be controlled with the aide of insecticides because there weren't any. The only method that could be used back then was by collecting and removing each beetle by hand. Obviously, farmers weren't keen on the idea of wasting valuable time picking up the beetles.

Farmers all over Queensland supported the move to import cane toads. Scientists did not. They tried to warn people of the risks, but many people felt the benefits outweighed the risks. They also couldn't see any other suitable alternatives.

Impact:
Sadly, the plan of introducing cane toads to eliminate the greyback and frenchie beetles backfired. Instead of eradicating the pests, the cane toad quickly became a pest itself and bred rapidly, spreading throughout the state in a westerly and southerly direction at an alarming rate.

The cane toads weren't very effective because the beetles they were supposed to eat rarely ventured onto the ground. Seeing as cane toads cannot jump high, the beetles weren't readily available for the cane toads to eat. Instead, the cane toads ate other insects and small animals. By 1940, an insecticidal spray was developed to combat the beetles and farmers lost interest in the cane toads.

Because the cane toad found it so easy to adapt to the Australian climate, it thrived. There are no natural predators of the toad in Australia and it seems that most animals who do prey on it are quickly repelled or even killed by the bufotoxin. Aswell as this, they breed extremely fast, with each pair of cane toad able to lay somewhere between 20,000 and 60,000 eggs in the one breeding season. It is also worth noting that a lot of unseasonal breeding has taken place since introduction into Queensland.

There are a large amount of negative impacts brought on by the introduction of this amphibian. There are little, if any, positive impacts. The widespread infestation of the toads is a man-made disaster. Even worse, the toads often compete for food with native Australian frog species and almost always win, and may sometimes eat the frogs they are competing with. A drop in the numbers of native Australian frogs has been blamed on the cane toad.

Control:
While the cane toad is not a declared pest and no one is legally required to destroy a cane toad upon sight, it is encouraged that people help control the toad in a humane manner. In 1989 the Brisbane City council formed a Cane Toad Eradication Committee in hope it would convince residents to help bring the problem under control.

Probably the best method of destroying a cane toad is by freezing it. When this is done, a toad becomes dormant because of the cold and soon dies while asleep. Another humane method is disposing the toad's eggs. This is quite simple, one only needs to put the eggs into their compost bin or garden, or perhaps even leaving them on the lawn to dry in the sun. However people should be absolutely certain that the eggs they are disposing of are infact the eggs of cane toads, and not of a native frog species.

No one should ever beat a cane toad to death. Apart from being cruel to the toad, bufotoxin may splatter you if you rupture one of the paratoid glands. Spraying the animal with chemicals (eg. bleach, hydrogen peroxide) is not humane behaviour. It may kill a toad quite fast, but the sensation can be similar to electrocution. A cane toad does not deserve to suffer simply because its species has become too widespread.

Today, the search is on for an effective method of biological control. The CSIRO has received plenty of funding in hope that they may be able to develop a way of killing cane toads that native frogs are immune to. Such a task is considered to be difficult and it could be decades before a solution is found.

References cited:
http://www.fbe.unsw.edu.au/exhibits/scientia/wwwjul96/jenkins/mjaustra.htm
http://www2.open.ac.uk/biology/froglog/FROGLOG-15-4.htm
http://rubens.anu.edu.au/student.projects/rabbits/wildanim.html
http://www.biotechnology.gov.au/biotechnologyOnline/environment/PestSpecies/e_TheCaneToad.htm
http://www.ozramp.net.au/~senani/aniausti.htm
http://animaldiversity.ummz.umich.edu/accounts/bufo/b._marinus.html
http://www.csiro.au/index.asp?type=faq&id=CaneToadControl
http://www.env.qld.gov.au/cgi-bin/w3-msql/environment/plant/animals/resultframe.html?id=13
http://www.nrm.qld.gov.au/factsheets/pdf/pest/PA21.pdf
http://www.smuggled.com/CanToa2.htm
http://www.fdrproject.org/pages/toads.htm
http://www.werc.usgs.gov/hq/invasive/toad-frog.html
http://www.agric.wa.gov.au/agency/Pubns/infonote/infonotes/toad.htm
http://members.tripod.com/%7Eiambic_ian/introspecies4.html
http://hometown.aol.com/kphairdeal/introspecies.html

Log in or register to write something here or to contact authors.