The black-headed monitor (Varanus tristis) is a relatively small species of monitor lizards native to Australia. Their average length is between 50 and 80 cm depending on location. V. t. tristis is the larger of two distinct subspecies, found mainly to the west of Australia. The freckled monitor (V. t. orientalis) is a smaller subspecies with a lighter, more distinct colouration confined mainly to eastern Australia. Clutch sizes range between four and 10 eggs. Males can be identified after sexual maturity (usually around two years of age) by a large cluster of spiny scales either size of the animal's vent. Female specimens lack these obvious protrusions and rarely possess more than a small number of spines only slightly larger than the surrounding scales.