Standing in front of a terrarium with a rare sighting of a vivid blue Common green tree frog (Litoria caerulea) sitting on a piece of wood, I was absolutely astounded. I have heard of green frogs with blue or yellow blotches but this one was blue all over!

The Latin word caerulea means “blue”, yet the frogs are green, so how did this name come about? The frog’s skin consists of two layers of pigment – blue and yellow – resulting in a green colour when mixed. When a green frog is preserved as a museum specimen, the preserving liquid – usually ethanol or formaldehyde (in the old days) – destroys the yellow layer and the specimen appears blue. As the first green tree frog was described from a preserved specimen, the scientist writing the description had no idea that the live frogs were actually green.

This change in colour is not only caused by the chemical process but some green tree frogs can have a genetic disorder, resulting in total or partial loss of one of the two pigment layers. The Common green tree frog is very bulky and adults measure up to 11 centimetres. These tree frogs are lime to olive green with a white underbelly. Sometimes, they have a few white dots on their back. Their eyes are golden with black pupils, and their toes and fingers have large suction pads used for climbing smooth surfaces. Common green tree frogs have two characteristic bulges behind their eyes and ears which are actually glands containing a milky liquid called “caerulein”.

Common green tree frogs are known to live for a long time. In captivity, some have been recorded to live for more than 20 years. On steamy summer nights, the males attract their partners by deep, short but loud barking calls, repeated several times. The males call from logs or rocks at the water edge but the actual spawning takes place in the water. The 200 to 2,000 eggs produced by a single female float on the surface in a mat of jelly but later sink to the bottom of the pool, where they hatch into tadpoles.