English name: Asian Water Monitor (aka “Common Water Monitor”)
Scientific name: Varanus salvator
Thai name: Hea
Description: To 3.21 meters long. Snout to base of tail is up to 1.1 meters. A massive, intimidating lizard, one of the largest in the world. The heaviest individuals can weigh over 50 kilograms and possibly a great deal more than that. Body is grey to black, often with varying spots and chain patterns of yellow-to-tan that fade with age. Neck is long and head is long and somewhat flattened. Has a notably large forked tongue that it often extends to sense its environment. Tail is higher than it is wide and very strong. Underbelly is somewhat lighter than rest of body.
Similar Species: No other lizard in our area has the enormous size or distinct appearance of the Asian Water Monitor.
Habitat: As their name implies, Asian Water Monitors are almost always found near water, including rivers, lakes, swamps, canals, and beaches. Within this constrant they can be found in a wide variety of habitats, including forests, grasslands, mangrove swamps, and agricultural areas. They are most common in coastal regions and become increasingly rare the further inland you go. They are very good swimmers and are known to swim long distances in the ocean, which can lead to the colonization of new islands. They are also good climbers and are often seen resting in trees at heights up to 10 meters. The Asian Water Monitor has adapted well to urban environments such as Bangkok’s parks, canals, and garbage dumps.
Place in the ecosystem: Are an adaptable and prolific predator that often targets smaller prey than you would expect, feeding on insects, snails, shellfish, crabs, fish, frogs, snakes, turtles, birds, and rodents. They will also hunt for the nests of birds, turtles, and crocodiles for their eggs. Monitors help keep the city clean by feeding on trash and dead meat, especially dead fish and other water animals that wash ashore. Young monitors can sometimes be eaten by large snakes.
Danger to humans: Asian Water Monitors do not prey upon humans, preferring to eat much smaller animals. However, a monitor that is grabbed or threatened by a human may use its teeth, claws, or tail to defend itself, and all three could inflict significant injury. If you are bitten by a monitor, it is important to clean the wound and apply antibiotic ointment immediately, as rotting flesh in the monitor’s mouth may lead to inflection. You should seek medical attention in the case of any serious bite in order to prevent infection. It is possible that very serious bites from the largest monitors may lead to fatalities.
Conservation status and threats: Is a widespread and common species in Thailand. Though they are sometimes killed for sport or out of fear, they adapt surprisingly well to urban environments for such a large lizard. They are a protected species in Thailand.
In other countries, Asian Water Monitors face heavy hunting pressure for their meat and skins, and the combination of overhunting and habitat destruction has led to their extermination in some places. They are considered to be nearly extinct in China, and their populations have seen serious declines in India, Bangladesh, and parts of Indonesia.
Interesting facts: The Asian Water Monitor is an inauspicious lizard in Thailand. Its Thai name is an insult referring to an evil thing. Superstitions state that it indicates bad luck, and some Thais will even avoid saying its name. The negative connotations associated with monitors may have to do with their eating of dead animals, their feeding upon household chickens and eggs, or their frightening appearance.
Wikipedia: Water Monitor
Ecology Asia: Malayan Water Monitor
Mampam Conservation: Water Monitor
Animal Diversity Web: Varanus salvator
Hong Kong University: Varanus salvator
IUCN Red List: Varanus salvator
Michael Cota, personal communication.
A Photographic Guide to Snakes and Other Reptiles of Peninsular Malaysia, Singapore and Thailand
A Field Guide to the Reptiles of South-East Asia
The Lizards of Thailand