The Cane Toad (Bufo marinus)
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.
The cane toad is very large; the females are significantly longer than males, reaching an average length of 10–15 centimetres (cm) (3.9–5.9 inches). “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 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 metres (66 ft) in length. The black eggs are covered by a membrane and their diameter is approximately 1.7–2.0 mm (0.067–0.079 in). The rate at which an egg evolves into a tadpole is dependent on the temperature: the pace of development increases with temperature.
Tadpoles typically hatch within 48 hours, but the period can vary from 14 hours up to almost a week. This process usually involves thousands of tadpoles—which are small, black and have short tails—forming into groups. It takes between 12 and 60 days for the tadpoles to develop into toad-lets, with four weeks being typical. Similarly to their adult counterparts, eggs and tadpoles are toxic to many animals.
When they emerge, toad-lets typically are about 10–11 mm (0.39–0.43 in) 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 (0.0255 in) per day, followed by an average rate of 0.373 mm (0.0147 in) per day has been observed.
Growth typically slows once the toads reach sexual maturity. This rapid growth is important for their survival—in the period between metamorphosis and sub–adulthood, 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, it is estimated that only 0.5 percent 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 of between 70 and 80 mm (2.8 and 3.1 in), while toads in Panama achieve maturity when they are between 90 and 100 mm (3.5 and 3.9 in) 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 (104–108 °F) and a minimum of around 10–15 °C (50–59 °F). The ranges can change due to adaptation to the local environment.
The cane toad has a high tolerance to water loss—one study showed that some can withstand a 52.6 percent loss of body water, allowing them to survive outside tropical environments. 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.
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. They however have 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.
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.
(Source: Wikipedia – The Free Online Encyclopedia)