Leaping Lizards! It's a water monitor

I especially advise Lumphini Park, as you are virtually guaranteed a sighting. Take your camera, keep your eyes open and you're sure to see an Asian Water Monitor Lizard (Varanus salvator) under a bridge, on the banks, in a tree or in one of the water pipes. The park is literally crawling with them! If you aren't based in Bangkok, most major waterways and lakes are home to them, so go and check 'em out.

All monitor lizards are in the family Varanidae and despite the incredible differences in size, color and behavior among the species, they are all in the genus Varanus. This is unusual in the animal kingdom, but genetic analysis has shown that all monitor lizards - from the enormous Komodo Dragon (Varanus komodoensis) that measures up to three meters and weighs up to 150 kilograms, to the tiny pygmy monitor (Varanus brevicauda) that measures at most 20 centimeters and weighs between 8-10 grams - are very closely related.

Asian Water Monitors live throughout Southeast Asia and are second in size only to the Komodo Dragon. They commonly grow to around 1.5 meters, but can also grow up to three meters and weigh up to 25 kilograms. Their varied diet and adaptability ensures their continued success. They eat almost anything -fish, carrion, smaller monitors, eggs, dog food and any other meat they can find. They are often aggressive and use their jaws, muscular tails and sharp claws as offensive weapons.

Like their crocodile cousins, monitor lizards cannot chew. Normally they simply open their gullet and swallow; but if an animal is too big to swallow whole, they can tear off pieces by chomping on it with their sharp, serrated teeth and shaking their head vigorously from side to side. The method is not very pretty, but it is very effective, so avoid getting close enough to become part of a demonstration. They tend to gorge themselves and will eat as long as food is available. After stuffing themselves, they allow the food to slowly digest.

Forked tongue, holes in the head

Towards the back of their head are two large holes that serve as ears; and although they have no 'auricle' (external ear) similar to the external part of the ear of humans that funnels the sound, they do have quite good hearing.

Monitor lizards have a serpent-like, forked tongue. This suggests that monitors are the closest living relatives to snakes. Like snakes, they use their tongue to detect taste, to smell scent particles in the air and for navigation at night. They have an organ on the roof of their mouth called the Jacobson's organ, which interprets the scent particles. The lizard's forked tongue allows it to determine which direction a scent is coming from. This organ is so sensitive that they can pick up the scent of rotting flesh a kilometer or more away. Their large nostrils are deceiving, as they are for breathing only; smelling is done all with the tongue.

One major difference among lizards and snakes, however, is lizards have ears. Towards the back of their head are two large holes that serve as ears; and although they have no 'auricle' (external ear) similar to the external part of the ear of humans that funnels the sound, they do have quite good hearing.

Water monitors are semi-aquatic and are always found near water, so fish constitutes much of their diet. Their keeled tail, which acts as a rudder, makes them great swimmers. Other monitors are arboreal, semi-arboreal or terrestrial.

While swimming, they streamline themselves by keeping their legs close to their body and wave their strong tail from side to side, similar to the swimming motion used by crocodiles. This allows them to swim great distances in search of food.

The lifestyles of lovable lizards

Water monitors aren't very territorial and don't fight to protect a specific area from encroachment by others. As such, many lizards sometimes live together where food is plentiful. They are relatively gregarious and there tends to be more males in large populations than females. Sometimes the males outnumber the females two to one. Males are generally larger than females.

They reach sexual maturity after about two years when they are 120-130 cm in length. They normally live for 15 to 20 years; but in captivity they often live up to 25 years. As with all reptiles, they never stop growing. Their ultimate size is dictated by the availability of food supplies.

Females can reproduce at any time of the year, but they generally breed at the beginning of the wet season. The female lays up to 40 eggs per year in two or more clutches. The eggs are soft and leathery and once laid, the hatchlings are left to survive on their own. In wild areas the females use their sharp claws to dig out nests in termite or dirt mounds, but anywhere the female can lay her clutch will suffice, as long as it's buried in a temperature controlled area and outside a flood plain.

When the eggs hatch, the youngsters are generally brightly colored and head for the trees. Hatchlings are rarely seen, as they are very secretive and must keep away from adult monitors to avoid becoming a nice snack. If you walk around Lumphini park or the Dusit zoo, you may be lucky to see young monitors, but they won't be in the water. They will be hiding in bushes and will be quick to scamper up a tree. I know, because I tried to catch some recently and they are fast little critters!

The young eat insects until they are mature enough to fit frogs or eggs down their throat. But the same rules apply to the young - if it's mainly meat and they can swallow it, then it's on the menu!

Fighting for an opportunity

Adult monitors can be seen sparring with each other, often at breeding time. They push against each other while standing upright on their hind legs and wrestle each other to the ground. The winner - usually the biggest and strongest - gets to breed. They normally breed in water amid a lot of biting and scratching. Not very romantic, unless you are a monitor. To keep the Lumphini monitor numbers under control, many are routinely relocated to Chon Buri.

In Thai, the word for the water monitor is hia. That word is sometimes used as a very offensive term, similar to a curse word, so avoid using it unless it is clear that you are referring to the animal. It is also a Thai superstition that if a monitor lizard visits you at your home, it's a sign of bad luck. So to avoid using the offensive term or bringing bad luck to another, Thais often use the more polite tua ngoen-tua tong ["silver and gold (body)"] term to refer to the animal.

Although I haven't been bitten by one (yet!), I have been tail whipped and hissed at, but I still love 'em and I think this only adds to their wonderful character! You will think so too when you go to meet one, but watch out for that tail whip - it really hurts!

David Canavan has an MSc in Behavioral Ecology and teaches science, math and ICT at Garden International School. David is fascinated by science and loves animals, especially the dangerous kind; the more dangerous the better. You may contact David at davidc@gardenbangkok.com .