Varanus scalaris
Banded tree goanna

Varanus scalaris   Mertens 1941

This goanna was originally described as a subspecies of V.timorensis (i.e. V.timorensis scalaris). A year after Mertens recognised it as a separate species (1957a) he considered that the differences between similis and scalaris were too slight to warrant use of scalaris as a specific name (Mertens 1958). V.scalaris has bands over the back which are lacking in V.similis and the latter has slightly fewer rows of scales around the body (107-117 vs. 110-129). Furthermore, male V.scalaris have spines just behind the vent which are absent in both V.timorensis and V.similis (Schmida 1971, Storr 1980). Storr (1980) treated V.scalaris as a subspecies of V.timorensis but Storr et al (1983) refer to it as a separate species. Their colour picture of this animal shows no sign of bands over the back. The differences between scalaris and similis are not at all clear to me.

Varanus scalaris
This goanna is widespread throughout the tropical Northwest of Australia. They can be distinguished from V.timorensis by examination of the tail, which is round in cross section rather than compressed. They reach a maximum size of about 60cm TL. Colour and pattern vary enormously, suggesting that V.scalaris may turn out to be a complex of several species (Mertens 1958; Storr 1980). A race from central Queensland with rusty red stripes over the back (known as "V.pellewensis") is likely to be described as a new species. Specimens from the rainforests of northern Queensland have bright yellow or orange throats (Schmida 1971; Swanson 1976; Green & King 1993).  These lizards occur almost wherever there are trees and are said to be absent from some sandstone areas, treeless grasslands and semi-desert.

Smith (1927) commented on the climbing ability of this goanna and noted that they would not attempt to bite when captured. According to Shine (1986) V.scalaris is active only during the wet season. Schmida (1971) found 14 specimens in 50m2, all sheltering in hollow branches, and saw them hunting for large insects in trees. Christian and Bedford (1996) record finding between 1.5 and 3 specimens per hour in the woodlands east of Darwin, where they commonly shelter in wooden fence posts. Little is known of their diet. Four specimens examined by Losos & Greene (1988) contained a skink, a scorpion and some insects. Schmida (1971) reported that they could also eat small agamids, lizards and birds. He reports that a specimen 20cm TL attacked and swallowed the tail of a gecko almost the same size as itself. Cogger (1973) suggested that they ignored frogs which shared their tree hollows. In captivity both youngsters and adults will hang from branches by their tails (Ruegg 1974). A study of thermoregulation in this species (Christian and Bedford 1996) found that the lizards maintain higher body temperatures during the set season than the dry season.

Some races of V.scalaris can be sexed by looking for spines on either side of the males' vents (Mertens 1958), but according to Schmida (1971) this is not reliable for V.similis. Unlike the Timor monitor, the spotted tree goanna is an aggressive lizard and animals housed together will often fight fiercely. Cannibalism is not unknown. Males are particularly rough with females during courtship and can fatally injure their intended mates. Nevertheless captive breeding is quite possible if adequate space (at least 1m2 of floor area) and plenty of hiding places can be provided (Ruegg 1974; Broer & Horn 1985; Eidenmuller & Wicker 1991). Up to eight eggs are laid which hatch after 115-139 days at 26-30oC into 3.4-5g youngsters. The hatchlings have similar pattern and colouration to the parents. They do well on insects and tiny portions of rodents and will also accept small freshwater fish such as guppies. It may be necessary to raise hatchlings separately. Spotted tree goannas can live for more than 15 years in captivity (Bennett 1994b).