The cane toad (Rhinella marina), also known as the giant neotropical toad or marine toad, is a large, terrestrial true toad native to South and mainland Central America, but which has been introduced to various islands throughout Oceania and the Caribbean, as well as Northern Australia. It is a member of the genus Rhinella, which includes many true toad species found throughout Central and South America, but it was formerly assigned to the genus Bufo.
Historically, the 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, R. marina. It was one of many species described by Carl Linnaeus in his 18th-century work Systema Naturae (1758).[5] Linnaeus based the specific epithet marina on an illustration by Dutch zoologist Albertus Seba, who mistakenly believed the cane toad to inhabit both terrestrial and marine environments.[6] Other common names include "giant neotropical toad",[7] "Dominican toad",[8] "giant marine toad",[9] and "South American cane toad".[10] In Trinidadian English, they are commonly called crapaud, the French word for toad.
The genus Rhinella is considered to constitute a distinct genus of its own, thus changing the scientific name of the cane toad. In this case, the specific name marinus (masculine) changes to marina (feminine) to conform with the rules of gender agreement as set out by the International Code of Zoological Nomenclature, changing the binomial name from Bufo marinus to Rhinella marina; the binomial Rhinella marinus was subsequently introduced as a synonym through misspelling by Pramuk, Robertson, Sites, and Noonan (2008).[2][3] Though controversial (with many traditional herpetologists still using Bufo marinus) the binomial Rhinella marina is gaining in acceptance with such bodies as the IUCN,[1] Encyclopaedia of Life,[12] Amphibian Species of the World and increasing numbers of scientific publications adopting its usage.
Considered the largest species in the Bufonidae,[19] the cane toad is very large;[20] the females are significantly longer than males,[21] reaching a typical length of 10–15 cm (4–6 in),[20] with a maximum of 24 cm (9.4 in).[22] 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,[24] and can live considerably longer in captivity, with one specimen reportedly surviving for 35 years.[25]
The skin of the cane toad is dry and warty.[20] Distinct ridges above the eyes run down the snout.[14] Individual cane toads can be grey, yellowish, red-brown, or olive-brown, with varying patterns.[26] A large parotoid gland lies behind each eye.[20] The ventral surface is cream-coloured and may have blotches in shades of black or brown. The pupils are horizontal and the irises golden.[15] The toes have a fleshy webbing at their base,[20] and the fingers are free of webbing.[26]
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.[23] The tadpoles are small and uniformly black, and are bottom-dwellers, tending to form schools. Tadpoles range from 10 to 25 mm (0.4 to 1.0 in) in length.
The skin of the adult cane toad is toxic, as well as the enlarged parotoid glands behind the eyes, and other glands across its back. When the toad is threatened, its glands secrete a milky-white fluid known as bufotoxin.[49] Components of bufotoxin are toxic to many animals;[50] even human deaths have been recorded due to the consumption of cane toads.[28] Dogs are especially prone to be poisoned by licking or biting toads. Pets showing excessive drooling, extremely red gums, head-shaking, crying, loss of coordination, and/or convulsions require immediate veterinary attention.[22]
Bufotenin, one of the chemicals excreted by the cane toad, is classified as a schedule 9 drug under Australian law, alongside heroin and LSD.[51] The effects of bufotenin are thought to be similar to those of mild poisoning; the stimulation, which includes mild hallucinations, lasts less than an hour.[52] 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.[49]
Since 2011, experimenters in the Kimberley region of Western Australia have used poisonous sausages containing toad meat in an attempt to protect native animals from cane toads' deadly impact. The Western Australian Department of Environment and Conservation, along with the University of Sydney, developed these sausage-shaped baits as a tool in order 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.
Many species prey on the cane toad and its tadpoles in its native habitat, including the broad-snouted caiman (Caiman latirostris), the banded cat-eyed snake (Leptodeira annulata), eels (family Anguillidae), various species of killifish,[57] the rock flagtail (Kuhlia rupestris), some species of catfish (order Siluriformes), some species of ibis (subfamily Threskiornithinae),[57] and Paraponera clavata (bullet ants).
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). The tawny frogmouth (Podargus strigoides) and the Papuan frogmouth (Podargus papuensis)[58] have been reported as feeding on cane toads; some Australian crows (Corvus spp.) have also learned strategies allowing them to feed on cane toads, such as using their beak to flip toads onto their backs.[59][60]
Opossums of the genus Didelphis likely can eat cane toads with impunity.[61] Meat ants are unaffected by the cane toads' toxins, so are able to kill them.[62] The cane toad's normal response to attack is to stand still and let its toxin kill the attacker, which allows the ants to attack and eat the toad.[63] Saw-shelled Turtles have also been seen successfully and safely eating cane toads.
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, and some of the continental islands near Venezuela (such as Trinidad and Tobago).[64][65] 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 (109 yd) of shoreline, 1 to 2% of the density in Australia.
