Cane Toad (Rhinella marina): Facts, Toxins and Invasion

Appearance

A cane toad is unmistakably big and solid. Its skin is dry and covered with warts, and its color ranges from gray and olive-brown to yellowish or reddish-brown, often with darker blotches. The belly is cream with some darker speckles. The eyes are golden with horizontal pupils, and bony ridges run from above each eye down toward the snout.

The most important feature is the pair of large, swollen parotoid glands on the shoulders, just behind the eyes. These triangular glands produce the toad’s toxic milky secretion. The hind toes are partly webbed, while the fingers have no webbing. Young toadlets are small and smooth, dark and often patterned, and they lack the large parotoid glands of adults. If you need to tell a toad from a frog, our frog vs toad comparison lists the key differences.

How big do cane toads get?

Most adult cane toads measure 10 to 15 cm (4 to 6 in) from snout to vent, the standard length for frogs and toads that leaves out the legs. Females are noticeably larger than males. The largest wild individuals reach about 24 cm (9.4 in). Most adults weigh well under 1 kg (2.2 lb), but exceptionally large toads can weigh more than twice that.

Toads tend to grow larger where their populations are less dense, which is often the case at the leading edge of an invasion. Read more about the giants, including a famous Swedish pet toad, in how big can a cane toad get?.

Habitat and range

The native range runs from the Rio Grande Valley of south Texas through Mexico and Central America to the central Amazon basin and southeastern Peru, along with islands such as Trinidad and Tobago. Cane toads prefer open country: grassland, savanna, open woodland and especially areas changed by people, such as farms, gardens, lawns, roadsides and drainage ditches. Dense rainforest seems to limit them.

Outside the Americas, the toad was deliberately released in many places as a supposed pest controller. Established populations now live in northern and eastern Australia, Florida, Hawaii, many Caribbean islands, Papua New Guinea, the Philippines, Fiji and other Pacific islands, Taiwan and several Japanese islands. In Australia, it has spread from Queensland across the Northern Territory into the Kimberley region of Western Australia and south into northern New South Wales.

The cane toad is tough. It survives temperatures from about 10–15 °C (50–59 °F) up to around 40 °C (104 °F), and it can lose about half of its body water and still live, which lets it cross dry country during the night.

What do cane toads eat?

Cane toads are opportunists with huge appetites. Most of their diet is insects and other invertebrates, especially beetles, ants, termites, bugs, snails and millipedes. They also eat small frogs, lizards, nestling birds and small rodents if they can catch them.

What makes them unusual among frogs and toads is that they also eat things that do not move. Cane toads eat carrion, plant matter, household scraps and pet food left outdoors. Most frogs only react to moving prey, but cane toads also use their sense of smell to find food.

Toxins and defense

When a cane toad is threatened, its parotoid glands and other skin glands release a thick, milky secretion. It contains a mix of toxins called bufadienolides, which act on the heart, along with other compounds. The toad does not attack; it simply relies on its poison. Faced with a predator, it may also puff itself up and raise its body off the ground to look bigger.

All life stages are toxic, from the eggs and tadpoles to the adults, though young toadlets carry less toxin. Native predators in the Americas have evolved alongside the toad, and many either avoid it or tolerate the poison. Animals that never met a toad before, such as many Australian lizards, snakes and marsupials, have no such defense. For a broader explanation of how toad poison works, see are toads poisonous?.

People have been seriously poisoned, and some have died, after eating cane toads or their eggs. Dogs that bite or mouth toads are also at serious risk. If a person may have swallowed toad toxin, seek emergency medical help immediately by calling 911 (US), 112 (EU) or 999 (UK).

Reproduction, life cycle and lifespan

Cane toads are prolific breeders. In the tropics they can breed at almost any time of year, while in cooler places they breed in the warm, wet season. Males gather at ponds, ditches and slow streams and call with a long, low trill, often compared to a distant engine or a dial tone. A male grips a female from behind in a mating embrace called amplexus while she lays her eggs.

A single female can lay about 8,000 to 25,000 eggs, and sometimes more, in long jelly strings that can stretch up to 20 m (66 ft) along the bottom of a pool. The eggs hatch within about one to three days. The small black tadpoles often gather in schools and take roughly 2 to 8 weeks, typically about four, to transform into toadlets only about 1 cm (0.4 in) long. Very few survive: an estimated 0.5 percent reach adulthood, partly because tadpoles and young toads eat each other.

Those that make it grow quickly and can breed within about a year in the tropics. In the wild, cane toads are generally thought to live around 10 to 15 years, although lifespans are hard to measure and many die much younger. In captivity, they can live longer.

Predators and threats

In the Americas, cane toads and their tadpoles are eaten by caimans, some snakes such as the banded cat-eyed snake, large fish, wading birds and even bullet ants. Opossums appear to tolerate the toxin.

In Australia, a few predators have learned to eat toads safely. Some crows and kites flip toads over and eat the nontoxic organs, rakali (Australian water rats) remove the toxic skin and glands with surprising precision, and meat ants swarm and kill young toads. The red-bellied black snake has even evolved greater resistance to the toxin in areas where toads have lived for decades.

Conservation status

The IUCN Red List classes the cane toad as Least Concern, in an assessment published in 2009. It is widespread and abundant in its native range and has no major threats there. Taxonomists have also proposed splitting the species: since 2016, some treat the toads of Mexico, Central America and northwestern South America as a separate species, Rhinella horribilis, leaving the name Rhinella marina for the populations east of the Andes. Many sources, including this article, still use the broader traditional definition.

The cane toad as an invader

The cane toad was introduced to Puerto Rico, Hawaii and other islands to eat beetles that damage sugarcane. Encouraged by these introductions, Australian sugar scientists brought 102 toads from Hawaii to Queensland in 1935. The toads did not control the beetles, but they spread over more than a million square kilometers of northern Australia, and their poison has killed large numbers of native predators such as northern quolls, goannas and freshwater crocodiles. The full story is told in why are cane toads a problem in Australia?, and you can see which animals the toad threatens in our list of Australian animals.

In the United States, the cane toad is native only in south Texas but is invasive in central and south Florida and in Hawaii. Read are there cane toads in Florida? to learn where they live and how to tell them from native toads.

Relationship with people

Beyond its use as a would-be pest controller, the cane toad has had a long and odd history with people. In the mid-20th century, toads of this and other species were used in laboratories for human pregnancy tests, because a male toad releases sperm within a few hours when injected with urine from a pregnant woman. The toad has also been widely used in teaching and research on amphibian physiology, and its genome has been sequenced to study how it adapts so quickly to new places.

In Australia, the toad has become a cultural icon as well as a pest. The 1988 documentary Cane Toads: An Unnatural History made it famous worldwide, and many communities in northern Australia organize volunteer groups to monitor its spread and protect native wildlife.

Myths and facts

Myth: cane toads squirt poison at people. Toads do not aim their poison. Under strong pressure the glands can ooze or spray a little secretion a short distance, which is why the eyes should be kept well away.

Myth: the cane toad is a marine animal. Its scientific name, marina, comes from an 18th-century belief that it lived in the sea. It is a land toad that breeds in fresh or slightly brackish water.

Fact: invasion-front toads have evolved. Toads at the leading edge of the Australian invasion have longer legs and travel farther each night than toads in older populations, one of the clearest examples of rapid evolution in an invasive species.