The Cane Toad is tough and adaptable, as well as being poisonous throughout its life cycle, and has few predators in Australia.
Cane Toads (Rhinella marina) 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.
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.
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.
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 history 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.
Cane Toads can breed in most still or slow-flowing water, and tolerate salinity levels up to 15%. Male Cane Toads start calling for mates after the first summer storms (in Australia that is about September) or when water temperatures reach 25º C. The choruses peak in January and finish by March. The males congregate after dark around shallow water and mount females as they arrive at the water's edge. The male grips the female in the armpits (this is called axillary amplexus) and she releases her eggs, which are fertilised externally by the male's sperm.
Females lay 8,000 to 35,000 eggs at a time and may produce two clutches a year. The eggs hatch within 24-72 hours and the tadpole stage may last from three to twenty weeks, depending on food supply and water temperature - generally a range of 25-30ºC is needed for healthy development. The tadpoles gradually change (metamorphose) into toadlets 1-1.5 cm in length that leave the water and congregate in large numbers.
Toads in the tropics grow very quickly and may reach sexual maturity within one year, but in temperate southern Queensland they mature in 18 months to two years. An adult lifespan of at least five years has been recorded in wild Cane Toads; captive individuals have lived for up to 15 years. Only about 0.5% of Cane Toad individuals that hatch from eggs survive to reach sexual maturity and reproduce.
It is a prolific breeder, requiring only a small pool of water of almost any nature.
Cane Toads were introduced to Australia to eat French's Cane Beetle and the Greyback Cane Beetle. The 'whitegrub' larvae of these beetles eat the roots of sugar cane and kill or stunt the plants. The Australian Bureau of Sugar Experimental Stations imported about 100 toads from Hawaii to the Meringa Experimental Station near Cairns. The toads bred quickly and more than 3000 were released in the sugar cane plantations of north Queensland in July 1935.
At that time, some naturalists and scientists warned of the dangers of liberating Cane Toads in Australia. The protesters included a former New South Wales Government Entomologist, W W Froggatt, and an Australian Museum Curator, Roy Kinghorn. Their protests resulted in a brief moratorium on the release of toads, but releases resumed in 1936.
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.
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.
Scientists at the CSIRO Animal Health Laboratory in Victoria have been searching for biological controls of Cane Toads and in 2001 they began investigating gene technology as a mechanism of control. Scientists at the University of Adelaide have isolated a sex pheromone in a native Australian frog; they hope that a similar pheromone will be found in Cane Toads and that it could be used to disrupt their breeding cycle.
The main controls on the spread of Cane Toads in southern Australia are quarantine checks and public awareness and response. One publicity campaign on the north coast of New South Wales resulted in 100 people collecting more than 900 Cane Toads.
If you think you have seen a Cane Toad, please catch it or report your sighting to a National Parks office or your state museum. It is important to confirm the identity before disposing of a suspected toad, because two-thirds of suspects turn out to be harmless native frogs (such as the Banjo Frog) that need our protection.
Danger to humans
All stages of the Cane Toad's life-cycle are poisonous. The poison 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 poison usually oozes out of the glands, but toads can squirt a fine spray for a short distance if they are handled roughly. The poison is absorbed through mucous membranes such as eyes, mouth and nose, and in humans may cause intense pain, temporary blindness and inflammation.
First aid treatment includes irrigating (washing with a lot of water) the eyes, mouth and nose if they have been exposed to toad poison. 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.
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