Monitor lizard belongs to the category of large lizard species. It is of the genus Varanus. They are native to Africa, Asia and Oceania. It is also an invasive species of America. As estimated, a total of 78 species of Monitor lizard is currently recognized.
Monitor Lizards in India
India is a home to about 75,500 animal species out of which the reptile count is about 420 species. India is diverse in terms of herpeto fauna which belongs to some 137 genera and 26 families, which is close to 8% of the world"s fauna. Out of these, reptile lizards are the most familiar. These lizards form one of the largest herpetofaunal groups in India, comprising about 158 species belonging to 8 of the 18 known families around the world. The Monitor Lizards in India are of four kinds. They are the Bengal Monitor lizard (Varanus bengalensis), Desert Monitor Lizard (Varanus griseus), Yellow Monitor Lizard (Varanus flavescens) and Water Monitor Lizard (Varanus salvator). The Bengal monitor lizard is the most common in India.
Bengal Monitor Lizard
Monitor Lizard belongs to the kingdom of Animalia, phylum of Chordata, class of Reptilia, order of Squamata and family of Varanidae. The external nostril opening of the Bengal monitor lizard is slit-like and oriented near horizontal. It is positioned between the eye and the tip of the snout. The scales of the skin are rougher in patches and minute pits can be seen on the sides. These scales with micropores have glandular structures in the underlying dermal tissue and functions to produce a secretion which may be a pheromone-like substance. They have a protruded, forked tongue. Sensation is the basic function of this tongue rather than transportation of food down the throat, as ordinarily thought. Fat deposits in the tail and body help them in conditions when there is scarcity of food. Their lungs have spongy tissue which permits greater rates of gas exchange, a faster metabolic rate and higher activity levels. They have subpleurodont teeth. At the base of the teeth, the mandibular glands produce secretions with no toxicity.
Desert Monitor Lizard
The Desert Monitor Lizard belongs to the kingdom of Animalia, phylum of Chordata, class of Sauropsida, order of Squamata, suborder of Lacertilia, family of Varanidae, genus of Varanus and subgenus of Psammosaurus. They are about 1 meter in length, but can reach a total body length of almost 2 meters. Their bodies are long and robust, limbs are sturdy and the tails are long and powerful, which are used like a whip in defence. Their backs or tails have horizontal bands along with yellow spots across their backs. The nostrils have diagonal slits located farther back on their snouts, much closer to the eye than the tip of the snout. Their skin is suited to desert environment, with a variety of body coloration from light brown and yellow to grey. They are excellent swimmers, but are occasional water divers when it comes to hunting food. Their overall body size is dependent on the climate, the time of year, food supply and their reproductive state. The male desert monitor is generally larger and more robust than the female, but it is the female who is known to have a gentle look. Adult monitor lizard shed its outer layer of skin during the periods of molting to expand the overall body size. This process can take many months and happens around three times per year.
Yellow Monitor Lizard
A medium-sized lizard measures about 50 cm from snout to vent and about 100 cm, inclusive of tail. This monitor lizard has short and convex snout, measuring a little less than the distance from the anterior border of the orbit to the anterior border of the ear. Its nostril is oblique slit, a little nearer to the end of the snout than to the orbit. Its teeth are sub-corneal, but scarcely compressed. Even if its tail is feebly compressed, it is keeled above. The scales of the head are small and the median series of supraocular scales are slightly dilated, transversely. Scales on the upper surfaces are moderate, oval and keeled, the abdominal scales are smooth (in 65 to 75 transverse rows) and the caudal scales are keeled. The caudal keel is very low and has doubly toothed crest. This lizard is olive or yellowish brown above with irregular darker markings, which are generally confluent into broad cross bar. It has blackish temporal streak and yellowish lower surfaces with indistinct brown cross bars that are most distinct on the throat.
Water Monitor Lizard
They are known to be the world`s second-heaviest lizard, after the Komodo dragon. Their bodies are muscular with laterally compressed tails, which are long and powerful. Male water monitors are larger than their female counterparts. For males, breeding maturity is attained when they are a relatively modest 40 cm long and weigh 1 kg. For females, breeding maturity is attained when they are 50 cm long. Adults rarely exceed 1.5-2 m (4.9-6.6 ft) in length.
Distribution of Monitor Lizards in India
Dr. R.J. Rao of the School of Studies in Zoology in Jiwaji University in Gwalior, conducted a study on the distribution of Monitor Lizards in India, under a project titled- "Survey of the Conservation Status of Monitor Lizards (Varanus Sp) in India". The Trans Himalayan zone was not reported with any monitor lizard. This is because monitor lizards cannot survive in such extreme cold climate. The semi arid zone including some parts of Rajasthan, Gujarat, Madhya Pradesh and the whole Haryana and Punjab, was occupied by three species of Varanus- Varanus bengalensis, Varanus griseus and Varanus flavescens. The Indian desert was found to be occupied by two species Varanus bengalensis and Varanus griseus. This study also reported Varanus bengalensis from Himachal Pradesh, parts of Jammu & Kashmir and Uttar Pradesh. Though Varanus flavescens was reported from Haryana, no animal was located during the present study. Along the coastal zone, Varanus salvator was reported to be found in mangrove swamps of Sunderbans in West Bengal and Bhitarkanika in Orissa. It was also found to be the most common lizard in the Andaman and the Nicobar Islands.
According to this study, all monitors were reported diurnal, reaching their full activity level when the sum was up and their habitat has warmed up. The plains and the desert monitors were found to use their claws as tools to dig out dens. Their diet comprised of feeding on other animals. More specifically, the smaller species were found praying on insects, small lizard and the nesting of small mammals. This study also found a very special preference for eggs by the monitors.
Threat to Monitor Lizards in India
The survey mentioned above also found various uncontrolled activities causing threat to monitor lizards in India. The study found that these lizards were used to extract oil for medicines to cure body ailments, make musical instruments and arrange meat for food. Their population was also threatened in some places, due to the notion that they were poisonous, consequently leading to their death. Their skin was also targeted by hunters for illegal export through border countries like Bengladesh, Nepal and Pakistan.
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