Exotic Animals - Major Pests
Cane Toad
Family: Bufonidae (True Toads)
Order: Anura (aka Salientia)
Class: Amphibia
Scientific names: Rhinella marina
First Introduction of Cane Toads
Cane Toads are native to Central and South America. They were first introduced to Australia in 1935 when more than 3000 individuals were released into sugar cane plantations in northern Queensland. They were released as a means of controlling the introduced French’s Cane Beetle and the Greyback Cane Beetle, which were causing significant damage to sugar cane crops. Unfortunately, the Cane Toad did not control the insects and went on to become one of Australia’s most highly invasive species, currently occupying over 500,000km² of Australian mainland, with densities reaching up to 2,000 toads per hectare when Cane Toads first colonize a new area.
Current Distribution
In recent years, Cane Toads have spread rapidly throughout northern Australia. They are now located within Queensland, New South Wales, the Northern Territory, and there have been recent sightings just over the border in Western Australia.
The Cane Toad was first sighted in the Northern Territory in 1984. By 2001 the toads had reached southern Kakadu National Park and were in the river catchments surrounding the Park. By 2004-2005 they were detected in Darwin. Since their arrival in the Darwin region there has been greater interest from the community regarding Cane Toads.
Considerable activity has been invested in preventing Cane Toads from spreading into Western Australia. Since September 2005, the ‘Kimberley Toad Busters’ have spent a substantial amount of time collecting eggs, hatchlings, juveniles and adult Cane Toads. Areas in the western Top End, have been targeted during the early wet and early dry seasons. Between 2005 and 2008 the group has collected almost 343,000 adult Cane Toads. Toad cage traps and toad-proof fence-lines have also been installed by FrogWatch in some locations within the area. It appears the spread of Cane Toads towards Western Australia has slowed down considerably, but it has not yet been stopped.
Cane Toads have managed to colonize some of the Northern Territory’s off-shore islands. For example, in the Gulf of Carpentaria, the Sir Edward Pellew Islands had their first recording of toads after the McArthur River flooded in 2001. It is believed the toads were washed out to sea on flood waters and some were washed right onto the shores of these islands. Protection of islands from all invasive species has become a priority for the NT Government.
Ability to Survive
Three primary reasons as to why Cane Toads have had considerable invasion success are because they can tolerate a wide range of environmental conditions, they are prolific breeders and they can be long-lived. Cane Toads are found in coastal heath and sand dune habitats along with on the margins of rainforests and in amongst the mangroves. They are found both in urban areas and out bush in grassland and woodland country. The ability of Cane Toads to breed and multiply is considerable with females producing 8,000 to 35,000 eggs at a time. Breeding occurs at least twice a year and normally takes place between June and January. In the right conditions they can breed throughout the year. Cane Toads will lay eggs in slow-moving freshwater streams and dams as well as in brackish water and temporary puddles. Tadpoles will hatch between 48 and 72 hours after being laid and, depending on the temperature and food availability, they will change into toads in 17 to 180 days. Toads grow particularly quickly in the tropics and can reach sexual maturity within one year. In captivity toads have been able to survive for up to 15 years. In the wild they have been known to breed for up to five years.
Cane Toads also have many other attributes which help them to survive so well. They are opportunistic, omnivorous feeders, and their diet comprises both living and dead matter such as plants, carrion, dog food, excreta of other animals, household refuse, small vertebrates, and a range of invertebrates. Other characteristics that add to their invasion success both in Australia and in other locations include their capacity to live for reasonable periods of time away from water, their ability to tolerate sea water for short periods, and their nocturnal activity. In their native countries, Cane Toads have diseases and parasites which keep their numbers under control, however these diseases and parasites are absent from Australia.
Impacts
The main threat posed by Cane Toads occurs when other wildlife attempts to prey upon them. When Cane Toads are threatened, they release a toxin (bufotoxin) from the glands behind the eyes and across their back. All stages of the Cane Toad’s life-cycle are poisonous, including the tadpole stage. This means that Cane Toads may negatively impact a wide diversity of wildlife. While it has been very difficult to quantify the losses to native animals as a result of Cane Toad invasion, evidence suggests that Northern Quolls, goannas, frogs, snakes, fish, Freshwater Crocodiles and egrets are particularly affected by the invasion. The Cane Toad has been nominated for listing as a key threatening process under the Environment Protection and Biodiversity Conservation Act 1999. Pet dogs and cats have also been known to mouth or bite Cane Toads. In some instances this has led to death when the pet has not received proper veterinary care.
In parts of Queensland, some populations of native animals were dramatically reduced when Cane Toads first arrived, although it seems that many have recovered since that time. This recovery has mainly been attributed to a change in behaviour, as some native animals have learned to avoid the toads as a food source.
With their voracious appetite, Cane Toads are known to be a threat towards beneficial insects such as the dung beetle and even towards bees which has created some management problems for beekeepers. Other threats to native wildlife include competition with native animals for food and resources; for example vertebrate insectivores such as small skinks appear to suffer. Cane Toads are also known to carry diseases such as salmonella which can spread to our native frog and fish species. They can also be a nuisance by blocking drains and fouling water holes, drinking troughs and swimming pools.
Signs of Poisoning
After ingestion, signs of poisoning in dogs and cats include copious amounts of frothy saliva, twitching, vomiting, shallow breathing, and collapse of the hind limbs. Death, through cardiac arrest, can occur within 15 minutes. It is suggested that for dogs and cats it is best to wash their mouth, eyes or nose out with lots of water (allowing them breaks to breathe) and then taking them to see a vet immediately.
In humans the poison may cause intense pain, temporary blindness and inflammation.
For further information, relating to reporting sightings of cane toads, capturing toads, taking part in toad musters or for information on trapping:
Phone: FrogWatch on 1800 243 564
Email: toadreport@frogwatch.org.au
Go to: www.frogwatch.org.au
