Cane toad

Appearance

The cane toad is very large; the females are significantly longer than males, reaching an average length of 10–15 cm. "Prinsen", a toad kept as a pet in Sweden, is listed by the "Guinness Book of Records" as the largest recorded specimen. It reportedly weighed 2.65 kg and measured 38 cm from snout to vent, or 54 cm when fully extended. Larger toads tend to be found in areas of lower population density. They have a life expectancy of 10 to 15 years in the wild, and can live considerably longer in captivity, with one specimen reportedly surviving for 35 years.

The skin of the cane toad is dry and warty. It has distinct ridges above the eyes, which run down the snout. Individual cane toads can be grey, yellowish, red-brown, or olive-brown, with varying patterns. A large parotoid gland lies behind each eye. The ventral surface is cream-coloured and may have blotches in shades of black or brown. The pupils are horizontal and the irises golden. The toes have a fleshy webbing at their base, and the fingers are free of webbing.

Typically, juvenile cane toads have smooth, dark skin, although some specimens have a red wash. Juveniles lack the adults' large parotoid glands, so they are usually less poisonous. The tadpoles are small and uniformly black, and are bottom-dwellers, tending to form schools. Tadpoles range from 10 to 25 mm in length.

Distribution

The cane toad is native to the Americas, and its range stretches from the Rio Grande Valley in South Texas to the central Amazon and southeastern Peru. This area encompasses both tropical and semiarid environments. The density of the cane toad is significantly lower within its native distribution than in places where it has been introduced. In South America, the density was recorded to be 20 adults per 100 m of shoreline, 1 to 2% of the density in Australia.

Behavior

The common name "marine toad" and the scientific name "Rhinella marina" suggest a link to marine life, but the adult cane toad is entirely terrestrial, only venturing to fresh water to breed. Tadpoles have been found to tolerate salt concentrations equivalent to at most 15% that of seawater. The cane toad inhabits open grassland and woodland, and has displayed a "distinct preference" for areas modified by humans, such as gardens and drainage ditches. In their native habitats, the toads can be found in subtropical forests, although dense foliage tends to limit their dispersal.

The cane toad begins life as an egg, which is laid as part of long strings of jelly in water. A female lays 8,000–25,000 eggs at once and the strings can stretch up to 20 m in length. The black eggs are covered by a membrane and their diameter is about 1.7–2.0 mm. The rate at which an egg grows into a tadpole increases with temperature. Tadpoles typically hatch within 48 hours, but the period can vary from 14 hours to almost a week. This process usually involves thousands of tadpoles—which are small, black, and have short tails—forming into groups. Between 12 and 60 days are needed for the tadpoles to develop into juveniles, with four weeks being typical. Similarly to their adult counterparts, eggs and tadpoles are toxic to many animals.

When they emerge, toadlets typically are about 10–11 mm in length, and grow rapidly. While the rate of growth varies by region, time of year, and gender, an average initial growth rate of 0.647 mm per day is seen, followed by an average rate of 0.373 mm per day. Growth typically slows once the toads reach sexual maturity. This rapid growth is important for their survival; in the period between metamorphosis and subadulthood, the young toads lose the toxicity that protected them as eggs and tadpoles, but have yet to fully develop the parotoid glands that produce bufotoxin. Because they lack this key defence, only an estimated 0.5% of cane toads reach adulthood.

As with rates of growth, the point at which the toads become sexually mature varies across different regions. In New Guinea, sexual maturity is reached by female toads with a snout–vent length between 70 and 80 mm, while toads in Panama achieve maturity when they are between 90 and 100 mm in length. In tropical regions, such as their native habitats, breeding occurs throughout the year, but in subtropical areas, breeding occurs only during warmer periods that coincide with the onset of the wet season.

The cane toad is estimated to have a critical thermal maximum of 40–42 °C and a minimum of around 10–15 °C. The ranges can change due to adaptation to the local environment. The cane toad has a high tolerance to water loss; some can withstand a 52.6% loss of body water, allowing them to survive outside tropical environments.

Habitat

The common name "marine toad" and the scientific name "Rhinella marina" suggest a link to marine life, but the adult cane toad is entirely terrestrial, only venturing to fresh water to breed. Tadpoles have been found to tolerate salt concentrations equivalent to at most 15% that of seawater. The cane toad inhabits open grassland and woodland, and has displayed a "distinct preference" for areas modified by humans, such as gardens and drainage ditches. In their native habitats, the toads can be found in subtropical forests, although dense foliage tends to limit their dispersal.

The cane toad begins life as an egg, which is laid as part of long strings of jelly in water. A female lays 8,000–25,000 eggs at once and the strings can stretch up to 20 m in length. The black eggs are covered by a membrane and their diameter is about 1.7–2.0 mm. The rate at which an egg grows into a tadpole increases with temperature. Tadpoles typically hatch within 48 hours, but the period can vary from 14 hours to almost a week. This process usually involves thousands of tadpoles—which are small, black, and have short tails—forming into groups. Between 12 and 60 days are needed for the tadpoles to develop into juveniles, with four weeks being typical. Similarly to their adult counterparts, eggs and tadpoles are toxic to many animals.

When they emerge, toadlets typically are about 10–11 mm in length, and grow rapidly. While the rate of growth varies by region, time of year, and gender, an average initial growth rate of 0.647 mm per day is seen, followed by an average rate of 0.373 mm per day. Growth typically slows once the toads reach sexual maturity. This rapid growth is important for their survival; in the period between metamorphosis and subadulthood, the young toads lose the toxicity that protected them as eggs and tadpoles, but have yet to fully develop the parotoid glands that produce bufotoxin. Because they lack this key defence, only an estimated 0.5% of cane toads reach adulthood.

As with rates of growth, the point at which the toads become sexually mature varies across different regions. In New Guinea, sexual maturity is reached by female toads with a snout–vent length between 70 and 80 mm, while toads in Panama achieve maturity when they are between 90 and 100 mm in length. In tropical regions, such as their native habitats, breeding occurs throughout the year, but in subtropical areas, breeding occurs only during warmer periods that coincide with the onset of the wet season.

The cane toad is estimated to have a critical thermal maximum of 40–42 °C and a minimum of around 10–15 °C. The ranges can change due to adaptation to the local environment. The cane toad has a high tolerance to water loss; some can withstand a 52.6% loss of body water, allowing them to survive outside tropical environments.

Food

Most frogs identify prey by movement, and vision appears to be the primary method by which the cane toad detects prey; however, the cane toad can also locate food using its sense of smell. They eat a wide range of material; in addition to the normal prey of small rodents, reptiles, other amphibians, birds, and a range of invertebrates, they also eat plants, dog food, and household refuse.

Predators

Many species prey on the cane toad and its tadpoles in its native habitat, including the broad-snouted caiman, the banded cat-eyed snake, eels, various species of killifish, the rock flagtail, some species of catfish, some species of ibis, and "Paraponera clavata". Predators outside the cane toad's native range include the whistling kite, the rakali, the black rat and the water monitor. The tawny frogmouth and the Papuan frogmouth have been reported as feeding on cane toads; some Australian crows have also learned strategies allowing them to feed on cane toads. Opossums of the "Didelphis" genus likely can eat cane toads with impunity....hieroglyph snipped...

Meat ants are able to kill poisonous cane toads, an introduced pest, as the toxins that usually kill a cane toad's predators do not affect the meat ants. The cane toad's normal response to attack is to stand still and let their toxin kill the attacker, which allows the ants to attack and eat the toad.

Defense

The skin of the adult cane toad is toxic, as well as the enlarged parotoid glands behind the eyes, and other glands across their backs. When the toads are threatened, their glands secrete a milky-white fluid known as bufotoxin. Components of bufotoxin are toxic to many animals; even human deaths have been due to the consumption of cane toads.

Bufotenin, one of the chemicals excreted by the cane toad, is classified as a class-1 drug under Australian law, alongside heroin and cannabis. The effects of bufotenin are thought to be similar to those of mild poisoning; the stimulation, which includes mild hallucinations, lasts for less than an hour. As the cane toad excretes bufotenin in small amounts, and other toxins in relatively large quantities, toad licking could result in serious illness or death.

In addition to releasing toxin, the cane toad is capable of inflating its lungs, puffing up, and lifting its body off the ground to appear taller and larger to a potential predator.

Poisonous sausages containing toad meat are being trialled in the Kimberley to try to protect native animals from cane toads' deadly impact. The Western Australian Department of Environment and Conservation has been working with the University of Sydney to develop baits to train native animals not to eat the toads. By blending bits of toad with a nausea-inducing chemical, the baits train the animals to stay away from the amphibians. Researcher David Pearson says trials run in laboratories and in remote parts of the Kimberley region of WA are looking promising, although the baits will not solve the cane toad problem altogether.

Evolution

The common name "marine toad" and the scientific name "Rhinella marina" suggest a link to marine life, but the adult cane toad is entirely terrestrial, only venturing to fresh water to breed. Tadpoles have been found to tolerate salt concentrations equivalent to at most 15% that of seawater. The cane toad inhabits open grassland and woodland, and has displayed a "distinct preference" for areas modified by humans, such as gardens and drainage ditches. In their native habitats, the toads can be found in subtropical forests, although dense foliage tends to limit their dispersal.

The cane toad begins life as an egg, which is laid as part of long strings of jelly in water. A female lays 8,000–25,000 eggs at once and the strings can stretch up to 20 m in length. The black eggs are covered by a membrane and their diameter is about 1.7–2.0 mm. The rate at which an egg grows into a tadpole increases with temperature. Tadpoles typically hatch within 48 hours, but the period can vary from 14 hours to almost a week. This process usually involves thousands of tadpoles—which are small, black, and have short tails—forming into groups. Between 12 and 60 days are needed for the tadpoles to develop into juveniles, with four weeks being typical. Similarly to their adult counterparts, eggs and tadpoles are toxic to many animals.

When they emerge, toadlets typically are about 10–11 mm in length, and grow rapidly. While the rate of growth varies by region, time of year, and gender, an average initial growth rate of 0.647 mm per day is seen, followed by an average rate of 0.373 mm per day. Growth typically slows once the toads reach sexual maturity. This rapid growth is important for their survival; in the period between metamorphosis and subadulthood, the young toads lose the toxicity that protected them as eggs and tadpoles, but have yet to fully develop the parotoid glands that produce bufotoxin. Because they lack this key defence, only an estimated 0.5% of cane toads reach adulthood.

As with rates of growth, the point at which the toads become sexually mature varies across different regions. In New Guinea, sexual maturity is reached by female toads with a snout–vent length between 70 and 80 mm, while toads in Panama achieve maturity when they are between 90 and 100 mm in length. In tropical regions, such as their native habitats, breeding occurs throughout the year, but in subtropical areas, breeding occurs only during warmer periods that coincide with the onset of the wet season.

The cane toad is estimated to have a critical thermal maximum of 40–42 °C and a minimum of around 10–15 °C. The ranges can change due to adaptation to the local environment. The cane toad has a high tolerance to water loss; some can withstand a 52.6% loss of body water, allowing them to survive outside tropical environments.

Uses

Other than the previously mentioned use as a biological control for pests, the cane toad has been employed in a number of commercial and noncommercial applications. Traditionally, within the toad's natural range in South America, the Embera-Wounaan would "milk" the toads for their toxin, which was then employed as an arrow poison. The toxins may have been used as an entheogen by the Olmec people. The toad has been hunted as a food source in parts of Peru, and eaten after the removal of the skin and parotoid glands. When properly prepared, the meat of the toad is considered healthy and as a source of omega-3 fatty acids. More recently, the toad's toxins have been used in a number of new ways: bufotenin has been used in Japan as an aphrodisiac and a hair restorer, and in cardiac surgery in China to lower the heart rates of patients. New research has suggested that the cane toad's poison may have some applications in treating prostate cancer.

Other modern applications of the cane toad include pregnancy testing, as pets, laboratory research, and the production of leather goods. Pregnancy testing was conducted in the mid-20th century by injecting urine from a woman into a male toad's lymph sacs, and if spermatozoa appeared in the toad's urine, the patient was deemed to be pregnant. The tests using toads were faster than those employing mammals; the toads were easier to raise, and, although the initial 1948 discovery employed "Bufo arenarum" for the tests, it soon became clear that a variety of anuran species were suitable, including the cane toad. As a result, toads were employed in this task for around 20 years. As a laboratory animal, the cane toad is regarded as ideal; they are plentiful, and easy and inexpensive to maintain and handle. The use of the cane toad in experiments started in the 1950s, and by the end of the 1960s, large numbers were being collected and exported to high schools and universities. Since then, a number of Australian states have introduced or tightened importation regulations. Even dead toads have value. Cane toad skin has been made into leather and novelty items; stuffed cane toads, posed and accessorised, have found a home in the tourist market, and attempts have been made to produce fertilizer from their bodies.