Asian/Water/Common Water Monitor, Two-banded
Monitor, Rice/Ring/Plain/No-Mark Lizard
Among the largest lizards in the world, Malayan Water Monitors can
survive in habitats that wouldn't be able to support other large carnivores.
and wetland wildlife at
Sungei Buloh Nature Park
features: Large greyish lizards, adults grow to
over 2m long and weigh up to 25kg. Males are larger than
females. Juveniles are more colourful.
in Singapore: Quite common, particularly in habitats
World distribution: Asian
subcontinent from India (and Sri Lanka) to China, down
Southeast Asia to Indonesia, the Philippines, New Guinea
islands in the Indian Ocean and South China Sea.
Classification: Family Varanidae,
Suborder Sauria, Order Squamata.
The Water Monitor's
main hunting technique is to run after prey that it has spotted, rather
than stalking and ambushing. Like snakes, they have a forked tongue that
they stick in and out regularly to "smell" their prey and other
are so successful because they are cold blooded and hence make more
efficient use of food.
addition, they eat anything that they can swallow. From tiny insects,
to crabs, molluscs, snakes, eggs (of birds and crocodiles), fish including
eels up to 1m long. They also eat birds, rodents, small mouse deer,
even other monitor lizards. They are particularly fond of carrion.
They even eat rubbish, human faeces, and even dead bodies. They eat
prey almost as big as themselves: one 1.2m long ate a snake 1.3m long.
blooded creatures do not have cold blood. Instead, their blood tends
to match the temperature of their surroundings.
Warm blooded creatures have to burn fuel constantly to keep their
temperature constant. Cold blooded creatures don't and thus can get
by with less food.
Water Monitors are more active than reptiles of their size because
they are able to maintain an almost constant body temperature. They
do this by choosing appropriate micro-climates in their habitat; hiding
when it's hot and in warm places when it's cool at night.
Water Monitor Lizards are highly mobile. They swim well (keeping their limbs
to the side of the body, and propelling themselves through sinuous undulations
of the flattened tail). They have even been seen swimming far out at sea.
They can remain underwater for up to half an hour.
run fast for their size as they have powerful leg muscles. In fact, they
are faster than most of us can run.
also climb well, to search for food as well as to escape predators, using
their strong curved claws. The young usually stay in trees for safety. If
cornered up a tree, they will jump into the safety of a stream or river.
They usually hide in a burrow built in a river bank. The entrance starts
on a downward slope but then increases forming a shallow pool of water.
The average length of the burrow is about 9.5 m, the average depth is about
2m. In the burrow, the average temperature is around 26 degrees Celsius.
name "monitor" probably originated from the superstitious belief
that Nile monitors warned of the presence of crocodiles. Nile monitors
eat crocodile eggs and were therefore often seen near crocodile
|Water Monitors are rarely found far from water. Both
fresh and saltwater. They are particularly common in mangroves, banks
of large rivers. Also found in grasslands, forests, swamps, beaches
and even cultivated land. From sealevel up to 1,100m high. They are
among the first large vertebrates to colonise new islands.
Monitor Lizards breed rapidly. Larger females produce a larger clutch than
smaller ones, up to 40 eggs a year in 2 or more clutches. Mating involves
a lot of biting and scratching. Females lay their eggs 4 to 6 weeks after
breeding. 3 to 25 white, soft-shelled eggs are laid, with an average of
15 per clutch. Eggs are laid in termite mounds (both active or abandoned
mounds), along rotting logs or hollow stumps or in burrows. Eggs take 2.5-10
months or more to incubate.
Juveniles are more brightly coloured with bright yellow markings on the
body and yellow bands on the tail contrasting against a darker body. But
they are more secretive and less commonly seen. Males grow faster than females,
become longer and heavier. In ideal conditions, they reach maturity in 2
years at 1-1.3m for males and 0.5-1.2m for females. Water Monitors can live
for up to 15 years.
Role in the habitat: As scavengers,
Water Monitors keep the habitat neat and tidy, and also control populations
of their prey. They in turn provide food for larger carnivores such as crocodiles
and birds of prey. Small young Water Monitors are particularly vulnerable
even to large birds such as herons.
Water Monitors are a
source of protein and income to poor rural people. Sustainable harvesting
is possible because even in places where they are hunted, they are still
attacked, Water Monitors try to intimidate predators by lashing out
with their tails, inflating their throats, hissing loudly, turning
sideways and compressing their bodies. When cornered, they will bite
and claw. Unlike other lizards, they do not drop their tails in self
the throat to intimidate
Status and threats: Water Monitors are
not considered endangered although they are commonly hunted for their meat
and skin and have been exterminated over most of mainland India. Elsewhere,
populations have declined sharply. Habitat destruction also affects them.
Up to 1.5 million skins are legally exported each year mainly from Indonesia
to Europe, Japan and the US to be made into fashion goods. One explanation
why they remain plentiful despite this is becuase the skins of medium-sized
Monitors are preferred. Those of larger Monitors are too thick and tough,
thus possibly sparing large females who lay more eggs. Their meat is considered
delicious and a bewildering array of potions are made from various parts
of their bodies, ranging from cures for diabetes to aphrodisiacs and deadly
poisons used in assassinations. The gall bladder is brewed for a medicinal
tea to treat heart and liver problems. Skin ointments are made from the
rendered fat. In Sri Lanka, the locals protect them because they eat the
crabs that would otherwise undermine the banks of the rice fields.
- Merel J. Cox, Peter Paul van Dijk, Jarujin Nabhitabhata and Kumthorn
Thirakhupt, "A Photographic Guide to Snakes and Other Reptiles
of Peninsular Malaysia, Singapore and Thailand", New Holland,
1998 (p. 107: habits, habitat, photo).
- Kelvin K P Lim and Francis L K Lim, "A Guide to The Amphibians
and Reptiles of Singapore", BP Science Centre, 1992 (p. 97-98:
habits, habitat, photo).