Cane Toads in Australia
Cane toads (Rhinella marina) are large amphibians originally from Central and South America, introduced to Australia in 1935 to control cane beetle infestations affecting sugarcane crops. However, their introduction has led to significant ecological challenges, as cane toads have proliferated across northern Australia and pose a threat to native wildlife due to their poisonous nature, predation, and competition for resources. Their rapid reproduction enables females to lay thousands of eggs multiple times a year, contributing to their expansive population growth. Cane toads are known for their voracious appetites and can consume a wide range of food, further straining local ecosystems. They are particularly harmful to various native species, including quolls, goannas, and certain bird populations, leading to the extinction of local wildlife in some areas. Efforts to manage cane toad populations have evolved from eradication attempts to more sustainable strategies focused on population control and conservation of affected wildlife. Community education and management practices, including trapping and humane disposal, are now emphasized to mitigate their impact while protecting native species. Additionally, some native predators have adapted to consume cane toads without succumbing to their toxins, highlighting the complex interactions within Australian ecosystems.
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Cane Toads in Australia
Cane toads (Rhinella marina; formerly Bufo marinus) are large, warty amphibians that are native to Central and South America. They were introduced to Australia in 1935 to combat cane beetles that were damaging sugarcane plants. Since their introduction, they have spread throughout northern Australia and pose a threat to native species and ecosystems due to their poisonous venom, predation and competition for food and habitat. Because of their large numbers and tendency to congregate in built environments, they are considered a nuisance to humans. They also pose a deadly threat to domestic animals, such as dogs and cats.
Cane toads are prolific breeders and eaters. The female can lay two clutches a year, with between about eight thousand and thirty thousand eggs in a clutch. In comparison, native frogs typically have one clutch a year consisting of about two thousand eggs. Cane toads will eat almost anything and consume vast amounts of food items each day. They have few native predators and are immune to native diseases. They possess poisonous venom in their skin and in glands on their shoulders that can cause paralysis and death. Cane toads are able to defend themselves easily by releasing this venom when they are threatened or handled roughly.
Brief History
Insect infestation of sugarcane plants in Queensland was a major problem during the late nineteenth century. In response to local growers' concerns, the Queensland government established the Queensland Bureau of Sugar Experiment Stations (BSES) to address the problem. After scientists learned that cane toads were being successfully used to consume the beetles that infested sugarcane plants in Puerto Rico and Hawaii, BSES entomologist Reginald Mungomery travelled to Hawaii in June 1935 to obtain cane toads. He caught 102 cane toads and returned to Australia with them. He housed them at an experimental farm, where they rapidly reproduced. Within two months, he had over 2,000 cane toads. In mid-August 1935, he released 2,400 cane toads at various locations in and around Gordonvale.
Several scientists raised concerns about the release of cane toads as no studies had been conducted to identify their effectiveness in combating the beetles that harmed sugarcane plants in Australia or about their potential threat to other species and the environment. In December 1935, the federal government enacted a ban on releasing additional cane toads. The ban was lifted in September 1936 after sugarcane growers and the BSES lobbied the government.
The cane toad proved to be ineffective in combating the greyback and French's cane beetles that attacked sugarcane plants in Australia. Unlike the beetles in Hawaii and Puerto Rico, these native beetles had unique characteristics that proved a defence to cane toads. The greyback cane beetles rarely came in contact with the ground, and the French's cane beetles came out when cane toads were not active.
The cane toads continued to proliferate and spread throughout Queensland and then to the Northern Territory. By 2009, they had spread to Western Australia.
Impact
Cane toads present a threat to native wildlife and the environment for several reasons. Cane toads are predatory and eat insects, scorpions, spiders, marine snails, frogs, snakes and small mammals. They compete with other wildlife for food and habitat. Their sheer number and voracious appetites allow them to consume large quantities of food items, decimating the food supply in an area and wreaking havoc on the ecosystems of other wildlife. Other wildlife dies after eating or mouthing cane toads. Cane toads are poisonous to eat at all stages of their life cycles, with their eggs being most toxic.
By the early 2000s, cane toads had had a significant impact on several native species, including dingoes, quolls, goannas, crows, kookaburras, frog-eating skames and dragons (agamids), including the Gilberts dragon. According to the National Cane Toad Taskforce, local populations of the northern quoll had become extinct in the Northern Territory by 2005. Rainbow bee-eaters, geckos and beetles also had increased mortality that was attributed to cane toads. In some areas, cane toads adversely affected the ecosystems of an area by significantly reducing the population of an insect or other item that other wildlife relied on as a main staple.
Cane toads also pose a threat to humans, although there are no recorded human deaths caused by cane toad poison in Australia. They can transmit diseases, including salmonella, and can cause death to pets that attempt to interact with them. Likewise, they pose a threat to unsuspecting children. They congregate in large numbers, foul pools and other water sources, and can block drains.
Both the government and scientists have worked to find ways to address the problems caused by cane toads. The earliest methods focused on controls to reduce cane toad populations. In the early 1990s, scientists tried to eradicate cane toads by introducing a virus. The virus ended up killing native frog species, and its use was discontinued. Scientists have since conducted research in search of a gene that could be altered to prevent the maturation of the cane toads.
In 2004, the national government established the National Cane Toad Taskforce to review the threat posed by cane toads and tools to abate those threats, and to assess whether national intervention would be beneficial. It concluded there was insufficient data quantifying the impact of cane toads to warrant national action and recommended state and local short-term controls and management of cane toads rather than a national strategy. Recommended local controls include attracting, trapping and humanely disposing of cane toads to reduce their populations. A chemical spray that humanely kills cane toads was developed and became available in the early 2010s.
By the mid-2010s, the primary strategy focused on the conservation of wildlife affected by cane toads and the management of cane toads rather than eradication. This strategy was adopted because of the realisation it would be impossible to rid Australia of cane toads without harming other native wildlife. Management involves preventing the spread of cane toads to new areas through quarantine inspections and community education and awareness programs and quarantines. Inspections at borders can prevent the accidental transport of cane toads, which are prone to stowing away in tires, pots and other objects. Awareness and education programs inform people on how to properly identify cane toads and distinguish them from native frogs in order to prevent the inadvertent killing of native frog species. In addition, several native predator species had adapted to be able to eat cane toads without risk of poisoning. For example, by 2019, rakali, or Australian water rats, had developed a way to make an incision to eat the cane toads' hearts and livers while avoiding the toads' toxic skin and glands. In 2021, the government of New South Wales reported the best way to manage the cane toad was the set barriers and traps to catch and remove them by hand. A study from the University of Syndey recommended refrigeration and freezing as the most humane way to kill the toads.
By 2019, cane toads had also become a problem in the Torres Strait Islands. Experts guessed that they had probably been carried there by boat from Australia.
Bibliography
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