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The Cane Toad

2015 December 29. Tuesday.

intro

The marine toad or cane toad is a large, terrestrial toad native to Central and South America, but has been introduced to various islands throughout Oceania and the Caribbean, as well as Northern Australia. In this paper, we will discuss the following aspects of the cane toad:

taxonomy

The cane toad originally got its name from its use as biological control for sugarcane pests. It has many other names as well, including “giant toad”, because of its size, and “marine toad”, because of its binomial name, R. marina. This misleading name comes from Carolus Linnaeus, who described this species (along with many others) in his work Systema Naturae (1758). Linnaeus based the classification on an illustration by Dutch zoologist Albertus Seba, who mistakenly believed the cane toad to be both terrestrial and marine. Some other common names are: “giant neotropical toad”, “Dominican toad”, “giant marine toad”, and “South American cane toad”.

appearence and identification

The cane toad is quite big, with the average adult length being 10–15 cm (3.9–5.9 in), and larger toads are generally found in areas of lower population density. They have a life expectancy of 10 to 15 years in the wild, but can live much longer in captivity, with one specimen living to the age of 35.

Adult cane toads are sometimes confused with Australian frogs from the genera Limnodynastes, Cyclorana, and Mixophyes. You can tell them apart by their lack of big glands behind the eyes and lack of ridge between the nostrils and the eyes. Cane toads are also confused with the giant burrowing frog (Heleioporus australiacus), because both are large and warty in appearance. The giant burrowing frog, however, is identifiable by its vertical pupils and silver-grey (instead of gold) irises. In the United States, the cane toad is sometimes confused with the southern toad (Bufo terrestris). The souther toad, however, has two bulbs in front of the paratoid glands that the cane toad lacks.

life cycle

One might think from the common name “marine toad” and the scientific name Rhinella marina, that there is a link between the cane toad and marine life. However, the adult cane toad is entirely terrestrial, only going to fresh water for breedding.

The life of a cane toad begins as an egg, which is laid as part of long strands of jelly in water. Tadpoles typically hatch within 48 hours, but the period can vary from 14 hours to almost a week, and gets shorter as temperature increases. This process of hatching usually involves thousands of tadpoles forming into groups. Tadpoles develop into juveniles over the course of the next 12 to 60 days, usually about 4 weeks. When juveniles emerge, they grow rapidly until sexual maturity. This rapid rate is necessary as they are not poisonous and have very few defenses during this period.

diet

Most frogs identify prey by seeing movement, and the cane toad primarily identifies prey in this manner. Unusually, the cane toad also uses smell to find food. Perhaps because of this, they eat a wide range of material: in addition to the standard frog prey of small rodents, reptiles, other amphibians, birds, and a range of invertebrates, they have also been found to eat plants, dog food, and household refuse (Freeland, 1986).

defenses

The cane toad’s skin, paratoid glands (behind the eyes), and other glands across the back, are all toxic (Hayes, 2009). When a toad is threatened, its glands secrete a milky-white fluid called bufotoxin. Parts of bufotoxin are toxic to many animals, including humans. 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.

predators

The cane toad (in both adult and tadpole forms) has many predators in its natural habitat, including the broad-snouted caiman (Caiman latirostris), the banded cat-eyed snake (Leptodeira annulata), eels (family Anguillidae), various species of killifish, the rock flagtail (Kuhlia rupestris), some species of catfish (order Siluriformes), some species of ibis (subfamily Threskiornithinae), and Paraponera clavata (bullet ants). Some predators outside of its normal environment are the whistling kite (Haliastur sphenurus), the rakali (Hydromys chrysogaster), the black rat (Rattus rattus), the water monitor (Varanus salvator), the tawny frogmouth (Podargus strigoides), and the Papuan frogmouth (Podargus papuensis).

The cane toad’s natural defense (at least against insects) is to stand still and let the toxin soak in. This usually works, however, the meat ant is immune to the cane toad’s toxin. So what would be a defense instead allows the ants to attack and eat the toad.

distribution/environments

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, the rock flagtail (Kuhlia rupestris), some species of catfish (order Siluriformes), some species of ibis (subfamily Threskiornithinae), 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) have been reportrd as feeding on cane toads; some Australian crows (Corvus spp. have also learned strategies allowing them to feed n cane toads. Opossums of the Didelphis genus likely can eat cane toads with impunity.

Public Domain Dedication.