Wild water monitor (Varanus salvator) near Polonnaruwa, Sri Lanka.
There are several subspecies recognized and the species is also known by many other common names including Malayan water monitor, two-banded monitor, common water monitor, ring lizard, rice lizard, plain lizard, no-mark lizard.
However, they are most commonly called simply "water monitor" by many people. The problem with unspecific common names is that for instance there are also other Australian lizards with similar names like Mitchell's water monitor or Mertens' water monitor also sometimes called water monitors. But also their scientific name "Varanus salvator" causes some confusion because of the similarity with that of the crocodile monitor (Varanus salvadorii).
The Asian water monitor is semi-aquatic species capable of occupying a wide range of habitats but always near water. These lizards are often found in swamps, flat land or river banks where they build burrows reaching more than 9 m in length and 2 m deep. They are very capable swimmers and have long been known to cross sizeable bodies of water, which explains the species wide distribution. Males are bigger than females with mature males weighing up to 20 kg but usually average much less.
Some exceptional reports put these lizards at 75 up to 90 kg, but these remain unverified and unreliable. Even so, the Asian water monitor is considered the world's 2nd heaviest lizard species losing only to the massive Komodo dragon (Varanus komodoensis).
Description[]
Asian water monitors have muscular bodies with long, powerful and laterally compressed tails with a dorsal keel. Reportedly they grow up to 3 m in length, but most adults are on average only about 1.5 m long. They have very long necks and an elongated snout with the nostrils located close to the end. They also have powerful jaws, very sharp teeth used and claws, that they won't hesitate to use to defend themselves
On the top of the head, the scales are somewhat larger than those located on the back which are also keeled. They also have a black band with yellow edges extending back from each eye. The Asian water monitor color is usually a dark brown or blackish with yellow spots found on their underside. These yellow markings have the tendency to disappear gradually as they become older.
When hunted down by predators like large snakes such as the king cobra (Ophiophagus hannah) they will climb up trees using their powerful legs and long claws. But if this isn't enough to escape danger they jump from the tree into the safety of a stream or river in a behavior similar to that of the green iguana (Iguana iguana). In captivity, they have reached a lifespan of about 11 years but in the wild, it's probably much less.
Taxonomy
Today 4 subspecies are recognized by scientists, with some of its former subspecies elevated to full species status in 2007. These include the marbled water monitor (Varanus marmoratus), large-scaled water monitor (Varanus nuchalis) or the yellow-headed water monitor (Varanus cumingi). While the black water monitor (V. s. komaini) found in Thailand is now regarded as a synonym of Southeast Asian water monitor (V. s. macromaculatus) and not a subspecies.
Diet / Feeding
Like other monitor lizards, the Asian water monitor is a carnivore, consuming a wide range of prey. They will eat just about any animal they can overpower, kill and consume. Some of the most common prey includes small mammals in particular rats, birds and their eggs, crabs, fish, other lizards, frogs, snakes, turtles, tortoises, smaller juvenile or young crocodiles and their eggs.
The Asian water monitor can remain submerged for up to 30 minutes at a time while hunting for aquatic prey. They also feed on carrion, just like the Komodo dragon, and like them, they have also been known to dig up human corpses and feed on them. Thanks to their powerful legs they are extremely fast and like other monitors they usually pursue their prey while hunting instead of stalking and ambushing them. These monitors have on occasion been observed eating while holding prey like catfish with their forelegs like mammals and tearing off chunks of meat and separating the different parts for eating sequentially.
Reproduction
Although males are usually twice as large as females as adults, they reach sexual maturity when they are about only 40 cm in length while females mature at about 50 cm long. The breeding season occurs from April to October, however early in the season females are more receptive meaning that earlier fertilization increases their reproductive success. The clutch size is dependent on the female's size with larger specimens producing larger clutches than smaller ones. The Asian water monitor females usually deposit their eggs in rotting logs or stumps.
Conservation Status and Threats
The species has been assessed as Least Concern by the IUCN red list and is listed in CITES Appendix II. The most common lizard exported from Southeast Asia are monitor species which are traded globally. The asian water monitor is among the most exploited varanids, being used by humans for a variety of purposes. Hunted mostly for their skins, which are valued by the fashion industry to make fashion accessories like handbags, belts, and shoes.
Up to 1.5 million monitor lizard skins traded annually being shipped all over the world.They are also used by the traditional medicine as a remedy for eczema or other skin ailments, as an aphrodisiac. Water monitors are also killed for their meat and taken from the wild for the exotic pet trade. Roadkill and loss of habitat also take their toll on the species. But despite all this, they are considered a resilient species, most likely because the leather industry has no use for the tough skin of larger specimens including females, which produce larger clutches.
The Asian water monitor is a protected species in Thailand, Hong Kong and Nepal's Chitwan National Park. Water monitors are very common in Malaysia while hunting and habitat loss exterminated them from most of mainland India. While in Sri Lanka they are protected by local populations since they feed on crabs found on the banks of rice fields and maintain the crab numbers under control.