Family: Varanidae - Monitor Lizards
Order: Squamata (Sauria) - Lizards
Phylum: Chordata - Vertebrates
Red List status: Not listed
Water monitor, juvenile. Pulau Perhentian Kecil, Malaysia.
Snout-vent length: 3 m
The widest-ranging of the world's monitor lizards, the water monitor is found throughout tropical Asia, from India and Sri Lanka to southeastern China, and throughout Indonesia
The world's second-largest lizard, adult water monitors are robust with a long snout and a powerful tail that is flattened at the sides. Body colouration is a dark blue-grey or slate-grey, usually with rows of yellow ocelli or spots crossing the dorsum. The tail is typically strongly banded in yellow. These markings are typically most prominent in juveniles, which are also more slender than adults; in adult animals the markings may fade and the ground colour becomes darker. In some cases yellow markings are completely lost The lips are pale and barred with black, and black V-shaped markings along the underside give the throat and lower body a striped appearance when viewed in profile.
Similar species: The rough-necked monitor (Varanus rudicollis) possesses yellow markings only along the flanks, is more slender as an adult, and differs in colouration both dorsal and ventral colouration. This species also lacks the flattened snout of the water monitor. The harlequin monitor (Varanus dumerilli) has a round tympanum (elongated in the water monitor), a shorter snout, a reddish or orange forehead and orange markings on the throat. In the water monitor, the oval or rounded nostril is closer to the snout tip than to the eye orbit; in the Bengal monitor (Varanus bengalensis), the nostril is situated roughly half-way between the snout tip and the eye. The yellow spots in this species are smaller, more numerous and don't form regular rows; they also invariably persist into adulthood.
Commonly around waterbodies in a wide range of habitats, including canals and urban water features as well as swamp, river banks and dipterocarp forest.
Diet: The water monitor is a highly opportunistic carnivore. In common with many monitor lizards it will take carrion and the eggs of crocodiles and birds, and will also actively prey on rodents, fish, water birds, turtles and a variety of other vertebrate and invertebrate prey. Due to the animal's large size, it will reportedly eat adults of smaller monitor species. In many areas the lizard is treated as a pest species, as it will readily take domestic chickens.
Breeding biology: Clutches consist of between 5 and 30 eggs, each measuring up to 42.9 x 82.6 mm. Over the species' range, the incubation period varies widely from as few as 180 days to nearly a year (327 days). Hatchlings measure 18-30 mm.
As a widespread, adaptable and often abundant species the water monitor is not regarded as a species of conservation concern. However, the species is heavily-exploited for its skin and meat (estimated at over a million skins per annum - Das, 2006), and is persecuted as a pest in some areas.
The water monitor, like many widespread species, appears to represent a species complex of morphologically similar animals. In 2007, Philippine populations of the water monitor, as well as one on the Indonesian island of Sulawesi, were recognised as separate species (Koch et al, 2007).
Cox, M.J., van Djik, P.P., Nabhitabhata, J. and Thirakhupt, K. (1998) Snakes and other reptiles of Thailand and South-east Asia. New Holland (UK), London: 144 pp
Das, I. (2006) Snakes and other reptiles of Borneo. New Holland (UK), Londin: 144 pp
Das, I. (2004) Lizards of Borneo. Natural History Publications (Borneo), Kota Kinabalu: 83 pp
Koch, A., M. Auliya, A. Schmitz, U. Kuch & W. Böhme. (2007). Morphological Studies on the Systematics of South East Asian Water Monitors (Varanus salvator Complex): Nominotypic Populations and Taxonomic Overview. pp. 109-180. In Horn, H.-G., W. Böhme & U. Krebs (eds.), Advances in Monitor Research III. Mertensiella 16, Rheinbach