Common name: cane toad
Scientific name: Rhinella marina
Description: Compared with native frogs, the cane toad is heavily-built and large (up to 20cm). Colours range from brown to mustard, with its underside varying from white to yellow, mottled with brown or grey. Its head and face, with a distinctive ridge over each eye, are unlike any Australian frog. But cane toad tadpoles are similar to some native frog tadpoles.
The skin on the cane toad's back is warty but has a leathery feel. Its hands and feet are small, with no pads on the edge of its fingers. It has distinct leathery webbing between its toes but none between its fingers. The cane toad's most noticeable feature is its parotoid glands. On its head behind each 'ear', these poison glands are large and prominent.
When threatened or handled, the toad releases a toxin from these glands that is highly poisonous to native animals and most domestic pets. The cane toad can squirt the milky toxin from its glands up to one metre away. Animals often die if they swallow cane toad toxin.
Habitat and distribution of the cane toad
Cane toads can live in many environments and have one of the widest ranges of habitats of any toad. Originally from South America, the cane toad has been introduced to many countries as a biological control agent for agricultural insect pests.
In 1935, cane toads from Hawaii were released into far north Queensland canefields in a failed attempt to control greyback beetles which were devastating the sugarcane industry. Only 10 years later, the toad was in Brisbane and has now spread south to areas of New South Wales and west to the Northern Territory and Western Australia, where cane has never been grown.
Life history and behaviour
The cane toad mostly eats ants, termites and beetles but it's a voracious feeder and can eat a wide variety of insects, frogs, small reptiles, mammals and even birds.
Added to this, a cane toad can lose half its body weight through dehydration without dying. It will replace its body fluids when water becomes available.
Unlike many native frogs, the cane toad doesn't need special food or conditions to start breeding. Cane toad eggs are unlike those of native frogs. The small, black eggs of the cane toad form long, sticky strings. Native frog eggs form in clumps. The cane toad produces many more eggs than native frogs and toads. An individual attaches up to 35 000 eggs to water plants or debris in slow-moving or still water.
Cane toad tadpoles resemble some native tadpoles but differ in two ways. Cane toad tadpoles gather in large, slow-moving schools while native tadpoles are solitary. Also, native tadpoles develop lungs at an early stage, regularly rising to the surface to breathe. Cane toad tadpoles stay under water.
In ideal conditions, a cane toad can reach adult size in less than one year. The cane toad is also long lived; a cane toad has lived 16 years in captivity.
The cane toad has become a nuisance to people and an ecological threat to the environment. In 1935, 3400 young cane toads were released around Cairns, Gordonvale and Innisfail in far north Queensland. They were released in an attempt to control greyback beetles, whose larvae stunt sugarcane growth. At this time, insecticides weren't available and the only way farmers could control beetles was collecting them by hand.
But the introduction of the toads had little or no effect on the cane beetles. This is because greyback beetles are rarely on the ground where cane toads live.
In the wild, cane toads compete for food, shelter and breeding sites with native animals. This is thought to be an important factor in the decline of many native animals, particularly the decline in number of some native frogs. The toad is extremely toxic to other animals. The parotoid glands of the toad release toxin when the animal is provoked or squeezed, such as when in the mouth of a predator.
Research into the toad's impact is continuing.
How can it be controlled?
Cane toad control remains largely the responsibility of the individual. In 1989, Brisbane City Council started a cane toad eradication program which showed people how to control this pest.
Cooling in a fridge overnight or until they are unconscious and then freezing for at least 2 days has been suggested as the most humane way of killing cane toads. Toads should first be collected in a container that has air holes. When put into a fridge, a cane toad will become dormant as a reaction to the cold. It will eventually die in its sleep once placed in the freezer. It can then be placed in the compost bin or buried in the garden deep enough to prevent pets or native animals digging it up.
The CSIRO is investigating organisms for biological control. This would be difficult though, as any viral or bacterial agent used would have to be specific to the cane toad and not harmful to native animals.
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