The Australian name for monitor lizards, goannas form the family Varanidae. There are about 30 known species in the world, 20 of which occur in Australia.
Monitors are the largest of all lizards, some species reaching a length of over 2 meters. They have a wedge-shaped head, long neck, loosely folded skin and a broad, rather flattened body and tail. They are voracious, carnivorous lizards with slender, flicking forked tongues, strong limbs, a long neck and tail and scales which do not overlap.
Most are good climbers and all can swim well (some are semi-aquatic). Goannas will often run on their hind-legs though they are faster on all four. Their diet includes carrion, rabbits, lizards and sometimes snakes. One species has been used for the attempted biological control of rats in some Pacific islands.
All have sharp teeth on jaws and palate, and a bite may give rise to blood poisoning not from any venom, but from putrid food fragments in the mouth due to the goanna's diet of carrion. Rats, mice, young birds and eggs are also eaten.
The largest of all lizards, the Komodo dragon of Indonesia, Varanus komodoensis, which ranges in length from 2m to 3m, belongs to this family. The Australian name 'goanna' is probably derived from iguana, though iguanas are not closely related to varanids, and do not occur in Australia.
Monitors range in size from a total length of 20cm (the short-tailed goanna or monitor, V. brevicauda), to about 2.5m (the perentie, V. giganteus, though this length is exceptional). Apart from size and body pattern, all monitors are very much alike.
A terrestrial lizard, living in deep crevices and burrows in rocky country from the central coast of Western Australia to western Queensland, the perentie forages in sandy desert and claypans, and will climb trees.
It is brown, with large cream or yellow spots which tend to form rows, and the tail is compressed from side to side, almost from the base. The average total length of the perentie is 1.6 meters, of which about 90 cm is tail.
The lace monitor, V. varius, is one of the commonest arboreal lizards. It can reach a total length of 2 meters and is found in Eastern Australia, from Cape York to south-eastern South Australia. It is blue-black in colour with bands of yellow dots, but the patterning is variable. The eggs are laid in burrows in termite nests. It is essentially a tree dweller, though often seen on the ground.
Gould's goanna or sand monitor, V. gouldii, reaches a total length of 1.6 meters and is one of the most widespread of the goannas. It is very variable in colouring and pattern, and is found throughout Australia apart from some parts of the south east, but it avoids wet habitats. It is a terrestrial, burrow-dwelling species.
In contrast, the mangrove monitor, V. indicus, which can grow to a total length of 1 meter, is confined, in Australia, to the far north of the Nothern Territory and north east Cape York where it lives in mangroves and rainforest, feeding on insects, fishes, reptiles, birds and mammals, in and near water. It is dark coloured with specks of cream and yellow.
Two other aquatic species live in the extreme north: Merten's water monitor, V. mertensi, (1 meter in length), and Mitchell's water monitor, V. mitchelli, (60 cm).
The smallest monitor is the short-tailed species, V. brevicauda, which reaches about 20 cm in total length. It is a light-coloured species, with darker flecks, and lives in sandy deserts, in Spinifex or ground litter, in northern WA and the central eastern parts of the Northern Territory.
The New International Illustrated Encyclopaedia, Volume 3, 1954. Page 333.
Australian Encyclopedia, Collins Publishers, 1984. Page 388.
Concise Australian Encyclopaedia, Second Edition, 1986, Angus & Robertson. Page 208.