Varanus semiremex
Rusty goanna

Varanus semiremex     Peters 1869

Varanus semiremex
The rusty goanna is a very poorly known monitor lizard from the northern coast of Australia. It appears to be restricted to the eastern coast of Queensland where it is found in mangrove swamps, on coasts and along freshwater streams and swamps (Cogger 1981). Mertens (1958) records them from Woodstock and Coquet Island off Queensland. Dunson (1974) examined specimens from Townsville and Bowen in Queensland. Glauert (1951) includes the species in a key to the goannas of Western Australia and Mertens (1961) describes a specimen supposedly from the Ord River in the extreme north-east of Western Australia. This animal was similar to those from Queensland but had a longer tail (178% of SVL compared with 134-160% in Queensland). However since 1961 no further specimens from outside Queensland have come to light, so it must be presumed that the species is restricted to that state. Even in Queensland the species appears to be rare. Covaceviich (pers. comm.) reports that she has seen only six specimens in twenty years at the Queensland Museum. Wilson & Knowles (1988) report that those from northern parts of Cape York Peninsula are darker in colour and have a stronger pattern than those from further south. The rusty goanna is sometimes known as V.boulengeri (Kinghorn 1924a).

This enigmatic little goanna reaches a maximum size of about 60cm TL. James et al (192) give a maximum size of 27cm SVL and consider sexual maturity to be attained around 15cm SVL. Mertens (1961) reports a length of 23.5cm SVL (over 66cm TL) for his specimen from Western Australia. Swanson (1976) gives a maximum size of 75cm TL. Six specimens examined by Dunson (1974) weighed 150 - 294g. Bustard (1970) records collecting rusty goannas from seasonally flooded mangroves around Townsville, as does Dunson (1974). Hedley (in Kinghorn 1924a) found one running along a beach. Its favourite food appears to be crabs (Dunson 1974; Swanson 1976; Losos & Greene 1988; James et al 1992). Other prey include frogs, fish and insects. All prey found by James et al (1992) were aquatic in origin but Dunson (1974) suggested that small mammals are also included in the diet. The rusty goanna appears to be an arboreal species which lives in hollows and on branches of trees overhanging the water. According to Dunson, in the mangroves around Townsville they forage over exposed mudflats at low tide. This species is equipped with a salt gland that secretes sodium, chlorides and potassium, enabling lizards from saltwater environments to obtain all their freshwater by eating brackish-water prey. Examination of museum specimens led James et al (1992) to conclude that breeding occurs in the late wet season (between February and April). The only gravid specimen examined by them contained two eggs, but clutches can contain as many as 14 eggs (Horn in James et al 1992). Ritual combat of the rusty monitor is described by Horn (1985). Opponents lie vent to vent grasping each other with all four legs and attempt to flick each other over in the typical Odatrian manner

Little is known about the captive care of this species in captivity, the only published accounts being those of Peters (1968, 1969e) and Pollock (1982). They should be kept warm and provided with a large terrarium with plenty of branches to climb on and a pool of water at least large enough for the lizards to immerse themselves. They are said to be very peaceful and tame in captivity and will eat small mammals, birds and eggs as well as their usual aquatic prey.