Varanus varius

Lace goanna

Varanus varius    Shaw 1790

The lace goanna is the second largest lizard in Australia. It is widespread in eastern Queensland, eastern New South Wales and most of Victoria but is restricted to the extreme south-east of South Australia (Houston 1978). They also inhabit some islands off the eastern coast (e.g. Mackay 1959). Lace goannas will live wherever there are trees and are common in many areas (Kreeft 1886, Richardson 1976, Jenkins & Bartell 1980). Peters (1967) found them close to the middle of Sydney. Its habitat includes rainforest as well as many drier woodlands. As would be expected of such a ubiquitous lizard, its pattern varies between areas. A vividly banded form (sometimes known as V.varius bellii) is also found in parts of Queensland and New South Wales which lives alongside those of normal pattern. The ecological implications of the pattern change are unknown (but see Grundke & Grundke 1992a). Horn's (1980) suggestion that all banded animals are males has been discounted (Greer 1989).

Varanus varius
In 1886 Krefft suggested that lace goannas grow as large as 250cm. None of this size exist now and specimens of 200cm TL are exceptional. A lizard from Mallacoota, Victoria measured 75cm SVL, 192cm TL and weighed 14kg (Weavers 1988). Another from Healesville was 198cm long and weighed almost 20.5kg. It was found to have eaten four foxcubs, three young rabbits and three large lizards (Fleay 1950). In contrast, a large male caught by Stebbins & Barwick (1968) in the spring measured 150cm TL and weighed 4.2kg. Males grow larger than females and probably have larger home ranges (Carter 1990).

The lace goanna is a superb climber, equipped with massive strongly curved claws and can move through branches with great agility. Eggs and chicks of a large number of ground and tree nesting birds have been recorded as falling prey to the lace goanna (Lucas & Dudley 1909; Carter 1924; Barrett 1928 Hindwood 1926: Gogerly 1922 Hyem 1936; Broadbent 1910; Goulburnite 1908; Kaveny 1958). They may feed on birds to a greater extent than any other monitor lizard. Outside the nesting season a variety of mammals (including kangaroos, opossums and bats), snakes, lizards, turtle eggs, crocodile eggs, fish, spiders, snails and insects as small as ants are eaten (Krefft 1886, Vestjens 1977, Kennerson 1980, Mansergh & Huxley 1985, Webb 1982; Losos & Greene 1988; Webber 1993). They will also eat carrion, even when it is in a very advanced state of decay (Kennerson 1980, Ward & Carter 1988) and will forage in human rubbish (Rose 1974). Krefft (1886) reported finding "several pounds of bones" in the stomach of one individual. Peters (1967) thought that the diet of adults was comprised largely of rodents and reptiles. Vincent (1981) suggested that lace goannas feed purposely on berries.

The lace goanna is a very active lizard that searches for food both in trees and on the ground. When threatened they will invariable take shelter in the nearest tree and try to hide on the opposite side of the trunk as their aggressor. It seems likely that many large prey are caught after a chase over the ground. Horn (1981) found that males outnumber females by 8:1, but these animals are notoriously difficult to sex without internal examination. Ritual combat occurs in the typical bipedal manner (Twigg 1988; Horn et al 1994). In southern parts of Australia activity is reduced or halted during the cooler months. They shelter in burrows or tree hollows.

Mating occurs during the summer in temperate regions. Up to six males may court a female at the same time and generally only the largest is successful (Wilson 1987). Mating has been observed taking place continuously over a period of several hours (Tasoulis 1983; Carter 1990). Maximum clutch size is usually given as 12 (e.g. Cogger 1959, Bustard 1970) and mean clutch size of 8 has been reported (Carter in Boylan 1995) but clutches of 19 eggs have been recovered from termite mounds (Boylan, 1995). Eggs usually weigh 50-65g (Bredl & Schwaner 1983, Horn 1991), representing a total possible clutch mass of over 1000g (but see below). The eggs are deposited in an active termite mound when these are available, either on the ground or in a tree (e.g. Longley 1945; Cogger 1959, Bustard 1970, Tasoulis 1992). In New South Wales eggs overwinter and hatch after 6-7 months. How the hatchlings escape from their termite mounds has been a matter of some debate. They seem to lack the strength to break through the tough outer wall of the mound. Incidences of adult lace goannas excavating nests is high during the spring whilst the eggs are hatching and this behaviour may serve to release the youngsters (Carter 1989, Boylan 1995). However at present their is no published evidence that the maternal individual remembers the location of her nest and returns there after many months to release her young. A television documentary which purported to show the release of hatchlings from a termite mound by their mother used broad artistic license (Marven 1990). After their escape/release the youngsters may remain around the nest for a week or more before dispersing. Like other monitor lizards the youngsters are more arboreal in habit than the adults. Where termitaria are absent the eggs are deposited in burrows or possibly in hollow logs (Cogger 1959, Houston 1978). Lace monitors may remain in one area for most of their adult lives. Frauca (1966 in Greer 1989) records a specimen that lived in the same tree for several years. Similarly females may use the same termite mound regularly as a nesting site. Where suitable termitaria are in short supply they may be vigourously defended against other females (Carter 1989, Horn 1991). The very large clutch of 19 eggs reported by Boylan (1993) could represent the eggs of more than one female, suggesting that nesting sites may be shared under some circumstances. Weavers (1988) considered that in temperate areas lace goannas may reach great ages (well over 20 years), based on their extremely low growth rates. In captivity they are known to live for over 15 years (Flower 1937; Kennerson 1979).

The thermal biology of the lace goanna has been investigated in some detail. They are able to raise their body temperatures by up to 2oC above ambient temperatures using heat generated by respiration (Bartholomew & Tucker 1964). Critical thermal maximums of 43-44.5oC have been established and below 5oC they are completely inactive (Spellerberg 1972). Green & King (1993) record activity temperatures of 32.8-36.4oC which can drop to about 21oC at night.

Reproduction and artificial egg incubation have been reported by Markwell (1983) Bredl & Schwaner (1983) and Boylan (1995). Outside Australia only one captive breeding has been reported (Horn & Visser 1990, Horn 1991). An enclosure with at least 2.5m2 of floor space is required to house an adult specimen. As much height as possible should be provided to allow climbing. Hoser (1993a) maintained a group of seven adults in a 90m2 outdoor enclosure. Best results have been obtained with animals raised in captivity from an early age and originating from the same location. They do well on a mixed diet of insects, small mammals and birds with plenty of extra vitamins and minerals. Females may produce more than one clutch of eggs per year and need large amounts of food. Horn & Visser (1990) record that a female ate 15 chicks, 20 mice and 2 rats with a week of laying eggs! Pairs often tolerate each other very well, but separating and reintroducing animals may be necessary to trigger courtship behaviour. Larger animals will kill and consume smaller ones (Hoser 1993a). A nesting box (as described in Horn 1991) should be provided for the female to deposit her eggs in. Depending on incubation temperature they hatch after 184-317 days (Markwell 1983, Bredl & Schwaner 1983). At a constant 29oC they hatch after about 235 days (Horn & Visser 1989, Horn 1991). Youngsters measure 28-36cm TL and weigh about 35g, but significantly smaller hatchlings of 16-23g were recorded by Weavers (1988) and Boylan (1995). It is not clear whether this is due to incubation conditions or related to the size of the female. Hatchlings seem to prefer vertebrate prey to insects and can grow rapidly, reaching 30cm SVL and over 300g within ten months (Horn 1991, Horn & Visser 1991). The environmental conditions provided for lace goannas must take into consideration the natural habitat of the animals, which varies from moist and tropical in the north to seasonal in the south.