The cane toad (Bufo marinus), also known as the Giant Neotropical Toad or Marine Toad, is a large, terrestrial true toad native to Central and South America, but has since been introduced to various islands throughout Oceania and the Caribbean. It is a member of the subgenus Rhinella of the genus Bufo, which includes many different true toad species found throughout Central and South America. The cane toad is a prolific breeder; females lay single-clump spawns with thousands of eggs. Its reproductive success is partly because of opportunistic feeding: it has a diet, unusual among Anurans, of both dead and living matter. Adults average 10–15 cm (3.9–5.9 in) in length; the largest recorded specimen weighed 2.65 kilograms (5.8 lb) with a length of 38 cm (15 in) from snout to vent.
The cane toad has poison glands, and the tadpoles are highly toxic to most animals if ingested. Because of its voracious appetite, the cane toad has been introduced to many regions of the Pacific and the Caribbean islands as a method of agricultural pest control. The species derives its common name from its use against the cane beetle (Dermolepida albohirtum). The cane toad is now considered a pest and an invasive species in many of its introduced regions; of particular concern is that its toxic skin kills many animals—native predators and otherwise—when ingested.
Originally, cane toads were used to eradicate pests from sugarcane, giving rise to their common name. The cane toad has many other common names, including "Giant Toad" and "Marine Toad"; the former refers to its size and the latter to the binomial name, Bufo marinus. It was one of many species described by Linnaeus in his 18th-century work Systema Naturae (1735). Linnaeus based the specific epithet marinus on an illustration by Dutch zoologist Albertus Seba, who mistakenly believed the cane toad to inhabit both terrestrial and marine environments. Other common names include "Giant Neotropical Toad","Dominican Toad","Giant Marine Toad",and "South American Cane Toad".In Trinidadian English they are commonly called "Crapaud".
In Australia, the adults may be confused with large native frogs from the genera Limnodynastes, Cyclorana and Mixophyes. These species can be distinguished from the cane toad by the absence of large parotoid glands behind their eyes and the lack of a ridge between the nostril and the eye. Cane toads have been confused with the Giant Burrowing Frog (Heleioporus australiacus), because both are large and warty in appearance; however, the latter can be readily distinguished from the former by its vertical pupils and its silver-grey (as opposed to gold) iris. Juvenile cane toads may be confused with species of the Uperoleia genus, but their adult colleagues can be distinguished by the lack of bright colouring on the groin and thighs.
In the United States, the cane toad closely resembles many Bufonid species. In particular, it could be confused with the Southern toad (Bufo terrestris), which can be distinguished by the presence of two bulbs in front of the parotoid glands.
The cane toad is very large; the females are significantly longer than males, reaching an average length of 10–15 cm (3.9–5.9 in). "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 kilograms (5.84 lb) and measured 38 cm (15 in) from snout to vent, or 54 cm (21 in) 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.
The juvenile cane toad is much smaller than the adult cane toad at 5–10 cm (2.0–3.9 in) long. Typically, they 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 (0.39 to 0.98 in) in length.
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. Cane toads have a habit of swallowing their prey.
The adult cane toad has enlarged parotoid glands behind the eyes, and other glands across their back. When the toads are threatened, their glands secrete a milky-white fluid known as bufotoxin. Components of bufotoxin are toxic to many animals; there have even been human deaths 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. It is thought that the effects of bufotenin are similar to that 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.
Many species prey on the cane toad in its native habitat. These include the Broad-snouted Caiman (Caiman latirostris), the Banded Cat-eyed Snake (Leptodeira annulata), the eel (family: Anguillidae), various species of killifish the Rock flagtail (Kuhlia rupestris), some species of catfish (order: Siluriformes) and some species of ibis (subfamily: Threskiornithinae). Predators outside the cane toad's native range include the Whistling Kite (Haliastur sphenurus), the Rakali (Hydromys chrysogaster), the Black Rat (Rattus rattus) and the Water Monitor (Varanus salvator). There have been occasional reports of the Tawny Frogmouth (Podargus strigoides) and the Papuan Frogmouth (Podargus papuensis) feeding on cane toads. It is likely that an opossum of the Didelphis genus can eat cane toads with impunity.
The cane toad is native to the Americas, and its range stretches from the Rio Grande Valley in southern Texas to the central Amazon and south-eastern Peru. This area encompasses both tropical and semi-arid 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 metres (109 yards) of shoreline, 50–100 times lower than the density in Australia.
The cane toad has been introduced to many regions of the world—particularly the Pacific—for the biological control of agricultural pests. These introductions have generally been well-documented, and the cane toad may be one of the most studied of any introduced species.
Before the early 1840s, the cane toad had been introduced into Martinique and Barbados, from French Guiana and Guyana. An introduction to Jamaica was made in 1844 in an attempt to reduce the rat population. Despite its failure to control the rodents, the cane toad was introduced to Puerto Rico in the early 20th century in the hope that it would counter a beetle infestation that was ravaging the sugarcane plantations. The Puerto Rican scheme was successful and halted the economic damage caused by the beetles, prompting scientists in the 1930s to promote it as an ideal solution to agricultural pests.
As a result, many countries in the Pacific region emulated the lead of Puerto Rico and introduced the toad in the 1930s. There are introduced populations in Australia, Florida, Papua New Guinea, the Philippines, the Ogasawara and Ryukyu Islands of Japan, most Caribbean islands, Fiji and many other Pacific islands. including Hawaii.Since then, the cane toad has become a pest in many host countries, and poses a serious threat to native animals.
Other than the previously mentioned use as a biological control for pests, the cane toad has been employed in a number of commercial and non-commercial 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. There are also suggestions that the toxins may have been used as a narcotic 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. 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.
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; 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 approximately 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 1950s, and by the end of 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.