The three introduced frog species are Australian, and belong to the hylid tree frog genus Litoria.
Unlike the native frogs they have a visible external eardrum (tympanum), and a horizontal, not rounded, pupil. Only the whistling frog is similar enough in size or colour to be mistaken for a native frog. They all have loud calls, and an aquatic tadpole stage.
Whistling frog or brown tree frog
This frog (Litoria ewingii) was brought to Greymouth in 1875. It is widespread in both main islands and may still be extending its range. It is less reliant on water than its cousins. Its ‘weeeep eeeep eeeep’ call sounds like a cricket. Mainly light brown on the back, it can change from light to dark. It has a white stripe from armpit to jawline, and orange thighs. It grows to 5 centimetres long (snout to vent).
Green and golden bell frog
Introduced to the Auckland area in the late 1860s, this frog (Litorea aurea) has not moved far. It is currently found only in the North Island north of Gisborne. Its call is a drawn-out croak, and it is mainly green with gold or bronze patches. The back of the thighs and groin are bright blue, and the belly is smooth and white. It grows to about 9 centimetres.
Frogs and fungus
The lethal chytrid fungus disease, widespread in Australia, means the southern bell frog faces extinction there, and the green and golden bell frog may also be at risk. New Zealand could have been a refuge for them – but now the fungus has arrived. It was identified in the southern bell frog in Christchurch over the summer of 1999–2000 by researcher Bruce Waldman.
Southern bell frog
Introduced into Canterbury from Tasmania in the late 1860s, the Southern bell frog (Litoria raniformis) is the most widespread frog in New Zealand, found throughout the country. Its call is a series of short staccato croaks. It has a similar colour pattern to the green and golden bell frog but often has a warty back. A distinct cream-coloured fold runs backwards from the eye, and there is a pale stripe down the midline of the back. Like the green and golden bell frog, the groin and back of thigh are bright blue. It grows to about 10 centimetres.