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Ranoidea caerulea, the Australian green tree frog, is a large, heavy-bodied hylid frog best known for the plump, waxy-skinned look it gets from storing water beneath its skin. It is native to Australia and southern New Guinea, and its tolerance for people and buildings has made it one of the most familiar frogs across its range.
Identification
Adults are sizeable as tree frogs go, with body lengths of 70-115 mm (about 3-4.5 inches); Wikipedia gives a similar maximum of about 11.5 cm, with fully grown females slightly larger than males. The species shows a clear sexual size difference: females average around 100 mm while males average around 75 mm, making females noticeably the larger sex. Colour is variable rather than fixed, ranging from brown, brownish- or greyish-green, to bright emerald green depending on temperature and environment, so the “green” in the common name is only ever a starting point for identification, not a guarantee. A fatty ridge runs above each eye, alongside a golden iris with a horizontal slit pupil and a visible eardrum just behind the eye. The limbs are distinctive too: short, robust forelimbs contrast with very long hind limbs, and large, circular adhesive discs tip each digit, with fingers about one-third webbed and toes nearly three-quarters webbed. The sexes can also be told apart by throat: males carry a wrinkled, grey-to-yellow vocal sac, while females have a white throat with taut skin.
Habitat and range
The species ranges across Australia and southern New Guinea, and within Australia it is unusually widespread, occurring from the coast to the drier interior across Western Australia, the Northern Territory, Queensland, South Australia and New South Wales. It typically occupies seasonally dry or wet habitats and prefers moist forested environments, but it is not a habitat specialist: the frog is highly adaptable, also occurring in suburban and agricultural areas. That adaptability is the reason it turns up so often around people, since it readily enters human structures such as homes and water tanks while seeking moisture, especially in summer. A frog found sitting in a bathroom or letterbox in eastern or northern Australia during the hotter months is very often this species, drawn in by the damp, cool conditions plumbing and tanks provide.
Behaviour and breeding
The Australian green tree frog is nocturnal, emerging in the early evening to call and hunt, and it is notably docile and unafraid of humans, which partly explains how comfortably it shares houses, sheds and gardens with people. By day it retreats to cool, dark and moist shelter such as tree holes or rock crevices, and its skin exudes a waxy coating that helps reduce water loss through evaporation; during dry spells it can wrap itself in a cocoon of shed skin and mucus to conserve moisture further. It hunts mainly insects such as moths, cockroaches and locusts, but will also take spiders, smaller frogs and even small mammals including bats, using its sticky tongue on small prey and pouncing to push larger prey into its mouth with its hands.
Breeding runs from November to February, when males call with a low, slow “brawk-brawk-brawk,” repeated many times. A female lays between 200 and 2,000 eggs in a clutch, which initially float before sinking within 24 hours. Tadpoles hatch at around 8 mm and grow to about 44 mm before metamorphosis, a process that takes roughly six weeks. In captivity the species is long-lived for a frog, averaging around 16 years and sometimes exceeding 20.
Conservation
The IUCN category is shown in the facts box above. The species is not considered at elevated risk of extinction; its wide native range across Australia and southern New Guinea, combined with its documented tolerance of suburban and agricultural habitat, supports a large population and a broadly stable trend. Local populations still face pollution and predation by domestic cats and dogs in suburban areas, and like many frogs worldwide it can be infected by chytrid fungus, which causes the disease chytridiomycosis. The species has also been heavily collected for the pet trade: in 2002 alone around 75,000 individuals were exported from Indonesia.
Similar species
The Australian green tree frog’s large size, plump build and preference for buildings and water tanks distinguish it from most other Australian hylids, many of which are smaller and more strictly tied to natural wetland or forest habitat. Its variable colour, from brown through greyish-green to bright emerald, rules it out as a reliable field mark on its own; a body regularly exceeding 70 mm, a pronounced size difference between the sexes, large adhesive toe discs and comfort living close to people are what set it apart from smaller green tree frogs that avoid human structures.