About Varanus panoptes Storr, 1980
Varanus panoptes (the Argus monitor) is a ground-dwelling monitor species that somewhat resembles the widespread sand goanna (Varanus gouldii). Large dark spots run in rows along its back, becoming especially distinct at the center of the back, where they are interspersed with smaller, paler spots. Color bands form toward the tip of the tail. Overall body color is brownish in the nominate subspecies V. panoptes panoptes, and reddish in V. panoptes rubidus. Most Argus monitors have a yellow patterning over a brown or dark tan background, though individual coloration varies between individual lizards and by region of origin. This species shows strong sexual dimorphism: females reach an average total length of 3 feet (90 cm), while males reach an average of 4–5 feet (120–150 cm). The largest recorded specimens can reach 1.6 m (5 ft 3 in) in length and 7 kg (15 lb) in mass. It is the third largest lizard native to Australia, after the perentie and the lace monitor. V. panoptes panoptes is the larger of the described subspecies, while V. panoptes horni is smaller. The Argus monitor has a reasonably lean build, and does not develop the heavy body mass seen in many African and Asian monitor species. Compared to other monitor species, the Argus monitor has an unusually fast life cycle. While most large-bodied monitors take 2 or more years to reach sexual maturity, Argus monitors can reach maturity in less than 1 year, though this timeline varies between populations. Males grow faster than females and also have longer average lifespans; in the Kimberley region, male monitors have a mean age of 465 days, compared to 263 days for females. In Arnhem Land, Argus monitors lay between 6 and 13 eggs between January and February. Due to their close genetic similarity, Argus monitors can naturally hybridize with Gould's monitors, forming a stable hybrid zone. Argus monitors often use communal warrens, which are interconnected systems of underground burrows sometimes shared by multiple individuals; one study recorded at least 6 individuals using the same warren. These warrens may also support communal nesting, where multiple different females each dig their own separate egg burrows within the shared warren. This species digs helical nest burrows with an average depth of 2.6 meters, the deepest known burrow created by any vertebrate as of 2015. This deep nesting may function to protect eggs from temperature fluctuations, dehydration, and/or cannibalism by males during the 8-month gestation period. Varanus panoptes acts as an ecosystem engineer. Its high population density, high feeding rate, and generalist diet make it an important predator in its native ecosystems. While individual dingoes or black kites consume more prey per individual than individual Argus monitors, the total prey consumed by the entire Argus monitor population is higher because the lizards occur at much greater population densities: 25 monitors per square kilometer, compared to 0.15 dingoes per square kilometer or 0.2 kites per square kilometer. When Argus monitor populations decline after the arrival of invasive cane toads, populations of their prey increase; for example, common tree snakes (Dendrelaphis punctulatus) become 26 to 46 times more abundant, though this increase may also include impacts from toad-induced declines of other monitor species. In addition to their role as predators, the burrows dug by Argus monitors are used by many other animal species. Argus monitors themselves are preyed on by black-headed pythons (Aspidites melanocephalus) and olive pythons (Lialis olivaceus).
