Floodplains goanna, Argus monitor
The yellow-spotted monitor is a large (total length up to 1.5m for males, approx 90cm for females) heavily-built ground-dwelling monitor, dark brown to reddish-brown on the back with alternating bands of large black spots and smaller dark-edged pale yellow spots. The underside is pale but often marked with lines of spots extending from the pattern on the back. The tail is laterally compressed and the last quarter is pale with narrow dark bands.
Ground-dwelling invertebrates and smaller vertebrates are a large part of the diet of this species. They will also feed on venomous snakes, medium to large skink and dragon species, and even smaller monitor species. Carrion is readily taken too, and the species is known for digging up and feasting upon the eggs of freshwater turtles, sea turtles and even crocodiles – in fact, they are considered one of the biggest predators of crocodile nests across their range.
This species can be found across a variety of habitats, including coastal beaches, floodplains, grasslands and woodlands. They will live in relatively arid areas, however they are mostly associated with permanent water sources and are considered riparian.
Yellow-spotted monitors can be found across northern Australia from the Kimberley to Cape York Peninsula, and southwards through most of Queensland. There is also a subspecies found in southern New Guinea.
Yellow-spotted monitors are avid diggers, and spend a lot of their time hidden away underground. They are mostly terrestrial, and so a majority of their prey is chased down and overpowered on land. That said, they are also skilled climbers and great swimmers, and will forage for food in the water and in trees as well. They are fast runners, and will run up to 100 metres to a tree or burrow entrance if they feel threatened.
Yellow-spotted monitors will often ‘tripod’ in order to get a better idea of their surroundings or if they feel threatened, standing up on their hind legs and supporting themselves with their tail.
Yellow-spotted monitors are considered ‘vulnerable’ but in some parts of their range it’s a lot worse than that. The largest threat to the species without doubt is the ongoing spread and infestation of the northern parts of Australia by the highly poisonous Cane Toad (Rhinella marina). This large amphibian pest is seen by the monitor as a large, easy-to-catch prey item, and the monitors seem to be particularly susceptible to the poison. Cane toads are also poisonous at all stages of their life cycle as well. In some areas of the NT, a 90% loss of adult Yellow-spotted monitors has been recorded. Similar losses have been seen in other monitor species, such as the Mertens’ Water monitor.