History
Cane toads were deliberately introduced to Australia from Hawaii in 1935 in an attempt to stop French’s Cane Beetle and the Greyback Cane Beetle from destroying sugar cane crops in North Queensland. The Australian Bureau of Sugar Experimental Stations made the release of 101 cane toads at Gordonvale in Queensland in 1935. They were unsuccessful in controlling the cane beetles. Since then, the cane toads have spread rapidly, south into New South Wales, with one isolated community in Port Macquarie, and west into the Northern Territory. In March 2001 they reached the wetlands of heritage-listed Kakadu National Park.
Habitat
The native habitat of cane toads is in Central and South America. They are found in sand dunes, coastal heath, mangroves and around rainforests. In Australia, most cane toads are found
in urban areas, and in areas with grassland or woodland. They are basically a terrestrial animal but require access to water for rehydration and breeding.
Appearance
Cane toads are large, heavily built amphibians with a dry and warty skin.
Their colouring ranges between grey and olive brown and their belly is pale with dark, irregular spots.
Average-sized
adults are 10-15 cm long, but they can grow up to 23 cm or more.
Breeding
They breed in still or slow-flowing water often tangling the spawn around rocks or water plants. The appearance of cane toad spawn is unique in Australia and consists of long gelatinous strings with double rows of black eggs. Females lay 8,000 to 35,000 eggs at a time and usually breed twice a year. The eggs hatch in 48-72 hours into tadpoles. They develop into toadlets in between 17 days to 6 months. Cane toads need between 6 and 18 months to reach sexual maturity and have a lifespan of about 5 years.
Toxicity
Cane toads have large swellings on each shoulder, the parotoid glands, from where poison is squirted when threatened or handled roughly. They are toxic in all their developmental stages: eggs, tadpoles, toadlets and adult toads. The venom contains 14 different chemicals causing
rapid heartbeat, excessive salivation, convulsions and paralysis. No humans have died in Australia from cane toad poison. Cane toads have no known predator in Australia, with the
possible exception of keelback snakes. Freshwater crocodiles, goannas, tiger snakes, dingos and western quolls are known to eat cane toads, but have died from the venom secreted by the toad. Some animals turn the toads on their backs and attack the soft belly, which is only mildly
poisonous. Cane toads are not officially recognised as a threatening process in Australia, because not all States consider toads to be a problem. Only animals that are of national significance are officially recognised as pests. Although no extensive environmental monitoring studies have been undertaken, there is evidence of the environmental impacts of cane toads. A decline in quoll numbers and native frogs in areas where large numbers of cane toads are found has been
recorded. Cane toads eat mainly insects, but will eat any small creature that fits in their
mouth. They also eat honey bees and are likely to compete for food with native animals. In addition they may carry diseases that could be transmitted to native frogs and fishes. Current control activities Different control methods for pest animals include conventional control
techniques and biological control agents. The former have highlighted concerns in the community to develop more humane control methods of pest animals.
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The Cane Toad is tough and adaptable, as well as being poisonous throughout its life cycle, and has few predators in Australia.
Identification
Cane Toads are large heavily-built amphibians with dry warty skin. They have a bony head and over their eyes are bony ridges that meet above the nose. They sit upright and move in short rapid hops. Their hind feet have leathery webbing between the toes and their front feet are unwebbed. Adult Cane Toads have large swellings - the parotoid glands - on each shoulder behind the eardrum
Cane Toads may be grey, yellowish, olive-brown or reddish-brown, and their bellies are pale with dark mottling. Average-sized adults are 10-15 cm long. The largest female measured in Queensland was 24 cm long and weighed 1.3 kg. Male Cane Toads are smaller and wartier than females. During the breeding season males develop dark lumps (nuptial pads) on their first two fingers; these help them cling to a female while mating. Their mating call is a long loud purring trill.
Young Cane Toads have a smooth dark skin with darker blotches and bars, and lack conspicuous parotoid glands. They can be distinguished from some native Australian frogs because they sit upright and are active in the daytime in dense clusters.
Cane Toad tadpoles are shiny black on top and have a plain dark belly and a short thin tail. They are smaller (less than 3.5 cm long) than most native tadpoles and often gather in huge numbers in shallow water. Cane Toad spawn is unique in Australia. It is laid in long strings of transparent jelly enclosing double rows of black eggs. The spawn tangles in dense dark masses around water plants, and hangs in ropy strands if picked up.
Size range 15 cm
Distribution
The natural range of Cane Toads extends from the southern United States to tropical South America. They were deliberately introduced from Hawaii to Australia in 1935, to control scarab beetles that were pests of sugar cane. In 2002, Cane Toads occur throughout the eastern and northern half of Queensland and have extended their range to the river catchments surrounding Kakadu National Park in the Northern Territory. In New South Wales they occur on the coast as far south as Yamba, and there is an isolated colony near Port Macquarie.
Habitat
Cane Toads are found in habitats ranging from sand dunes and coastal heath to the margins of rainforest and mangroves. They are most abundant in open clearings in urban areas, and in grassland and woodland.
Behaviour and adaptations
Feeding and Diet
Cane Toads eat almost anything they can swallow, including pet food, carrion and household scraps, but most of their food is living insects. Beetles, honey bees, ants, winged termites, crickets and bugs are eaten in abundance. Marine snails, smaller toads and native frogs, small snakes, and small mammals are occasionally eaten by Cane Toads.The tadpoles of Cane Toads eat algae and other aquatic plants which they rasp off with five rows of tiny peg-like teeth. They also filter organic matter from the water. Large tadpoles sometimes eat Cane Toad eggs.
Other behaviours and adaptations
Adult Cane Toads are active at night during the warm months of the year. During the day and in cold or dry weather they shelter in moist crevices and hollows, sometimes excavating depressions beneath logs, rocks and debris. They can survive the loss of up to 50% of their body water, and can survive temperatures ranging from 5ºC - 40ºC.
Life cycle
Predators of Cane Toad tadpoles in Australia include dragonfly nymphs, water beetles, Saw-shelled Turtles and Keelback Snakes. Keelbacks also eat young toads; laboratory tests have shown that they can tolerate low levels of toad toxins. Young or adult Cane Toads are eaten by wolf spiders, freshwater crayfish, Estuarine Crocodile, crows, White-faced Heron, kites, Bush Stone-curlew, Tawny Frogmouth, Water Rat and the Giant White-tailed Rat. Some predators eat only the toad's tongue, or attack its belly and eat only the mildly poisonous internal organs.
Predators, Parasites and Diseases
The Cane Toad is tough and adaptable as well as being poisonous throughout its life cycle. It has few predators in Australia, which is bad news for competing native amphibians, and it may be responsible for the population decline of the few snakes and other species that do prey on it.
Management
Cane Toads are considered a pest in Australia because they:
"poison pets and injure humans with their toxins
poison many native animals whose diet includes frogs, tadpoles and frogs' eggs
eat large numbers of honey bees, creating a management problem for bee-keepers
prey on native fauna
compete for food with vertebrate insectivores such as small skinks
may carry diseases that are can be transmitted to native frogs and fishes."
Danger to humans and first aid
All stages of the Cane Toad's life-cycle are poisonous. The venom produced by the parotoid glands acts principally on the heart. No humans have died in Australia from Cane Toad poison but overseas, people have died after eating toads and even soup made from boiled toad eggs. Cane Toads are also poisonous to pets and in Hawaii up to 50 dogs a year have died after mouthing Cane Toads. Signs of poisoning through ingestion include profuse salivation, twitching, vomiting, shallow breathing, and collapse of the hind limbs. Death may occur by cardiac arrest within 15 minutes.
Australian native fauna that have been killed by eating or mouthing Cane Toads include goannas, Freshwater Crocodile, Tiger Snake, Red-bellied Black Snake, Death Adder, Dingo and Western Quoll.
A Cane Toad responds to threat by turning side-on so its parotoid glands are directed towards the attacker. The venom usually oozes out of the glands, but toads can squirt a fine spray for a short distance if they are handled roughly. The venom is absorbed through mucous membranes such as eyes, mouth and nose, and in humans may cause intense pain, temporary blindness and inflammation.
First Aid
First aid treatment includes irrigating (washing with a lot of water) the eyes, mouth and nose if they have been exposed to toad venom. Seek medical attention if symptoms persist. When handling any frog or toad, protect the eyes, wear gloves, and thoroughly wash hands before and after touching the animal.