Southern or Blotched Blue-tongued Lizard ( Tiliqua nigrolutea )

The blotched blue-tongued lizard is the largest skink found in Tasmania. It also occurs through the south-east of the Australian mainland. It is sometimes referred to colloquially as a "goanna". However, it is actually a skink and a member of the family Scincidae, which also includes all other smaller Tasmanian lizards except the mountain dragon. The scientific name refers to the colouring, black (nigro) and yellow (lutea).

Although common and widespread in Tasmania, these lizards are very secretive and relatively seldom observed in the wild. Like other reptiles, they warm their bodies by basking in the sun. To prevent themselves from becoming too warm, they "shuttle", or move backwards and forwards between a hiding place and open areas. For these reasons, little is known about their biology, although studies are currently being conducted at the University of Tasmania's School of Zoology

Blue-tongues are omnivorous. In captivity, they can be maintained on a varied diet of cat food, soft fruits such as banana or kiwifruit and snails. They are partial to strawberries, as many home gardeners will have discovered. Their presence in a garden ensures the demise of many garden pests such as slugs and snails.

Blue-tongues have an unusual body shape for a skink, with a stout body, relatively small limbs and a thick, short tail. Blue-tongues rarely lose their tails, unlike smaller skinks, in which tail loss is an anti-predator device. Blue-tongues use their characteristic threat display as a warning device. The animal expands its ribcage and turns side on in order to appear larger. At the same time it opens its mouth wide to hiss and display its startling blue tongue and pink mouth

Contrary to folk belief, these lizards are not poisonous, although an animal carelessly handled can give a nasty nip. Teeth are very small, but jaws are extremely strong. It is also untrue that marks reappear on the anniversary of a bite!

They are, like most reptiles, difficult to sex from external appearances. The males tend to be smaller (300-350g) than females (350-450g), which can grow as heavy as 650-700g in late pregnancy. The males also have proportionally broader heads and their tails tend to be thicker at the base. This is due to the musculature of the two hemipenes. With practice, it is possible to evert the hemipenes to confirm the sex of the animal. Adult males have a head and body measuring about 25-27cm, while mature females are likely to grow to 27-30cm. Some blue-tongues have been known to live as long as 20 years.

Like all reptiles in cooler climates, blue-tongues are active only during the warmer months. They are solitary animals, except during the mating season. The males emerge first after winter hibernation: in Tasmania this occurs in late September. The females emerge in late October. Mating occurs in November or December, depending on the weather. Our work at the University of Tasmania has shown that males begin to produce sperm during the previous autumn, so that only the final stages of sperm production occur in spring.

These lizards are viviparous, giving birth to 1-17 live young (depending on body size) in autumn. Some books suggest a clutch size of up to 25 young; from current studies, this seems unlikely. Additionally, producing a clutch of young represents a substantial drain on the mother's energy reserves. We now know that females only reproduce every 2-3 years, even though males mature sperm on an annual basis.

Although there is a simple placenta, most of the nutrition for the developing young is supplied by the large, yolky egg. Young are independent at birth, receiving little or no parental care, but will not be sexually mature themselves for four or five years.

Prepared by A/Prof Susan Jones and Dr Ashley Edwards
School of Zoology, University of Tasmania