| Desert Monitor | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Sauropsida |
| Order: | Squamata |
| Suborder: | Lacertilia |
| Family: | Varanidae |
| Genus: | Varanus |
| Subgenus: | Psammosaurus |
| Species: | V. griseus |
| Binomial name | |
| Varanus griseus (Daudin, 1803) |
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The Desert Monitor, Varanus griseus, is a species of monitor lizard of the order Squamata found living throughout North Africa and western Asia. Varanus griseus is divided into three distinct subspecies: Varanus griseus griseus (Grey Monitor), Varanus griseus caspius (Caspian Monitor), and Varanus griseus koniecznyi (Indian Desert Monitor). They are possibly as venomous as snakes, and they eat anything from beetles to cobras and vipers depending on their size. Varanus griseus is not comfortable in captivity and only rarely has successful breeding in captivity been documented. [1]
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Varanus griseus monitor lizards normally display a variety of body coloration from light brown and yellow to grey. They average around approximately one meter in length, but can reach total body lengths of almost two meters. These lizards can also have horizontal bands on either their back or tail along with yellow spots across their back. Their young are normally a brightly colored orange and have distinctive bands across their back which may be lost as their mature into adulthood. Their nostrils are slits that are located farther back on their snout (closer to the eyes than the nose), and their overall body size is dependent on the available food supply, the time of year, environmental climate, and reproductive state. Males are generally larger and more robust than females, but females have a more gentle look about them. Those differences allow males to be distinguished from females from a distance without careful inspection. Adult monitor lizards also go through periods of molting in which they shed their outer layer of skin in order to expand their overall body size. This process can take several months and happens approximately three times per year. Their skin is designed for the desert environment in which they live, and they are excellent swimmers and divers and have been known to enter the water occasionally to hunt for food. [2]
The Varanus griseus griseus subspecies (Grey Monitor) has 5-8 narrow grey bands on the back as well as 19-28 bands on the tail. Its tail is more rounded that those of the other subspecies and the final size of the adults depends on the habitat they are living in. Their coloration can be anywhere from simple grey (in desert-like ecosystems) to brilliantly colored (in areas with large amounts of plant growth). Their most common prey consists of lizards and snakes, but can branch out to include ground-nesting birds and other small mammals. [1]
The Varanus griseus caspius subspecies (Caspian Monitor) has 5-8 bands on the back, 13-19 bands on the tail, a plain tail tip, and approximately 143 rows of scales in the middle section of their body. They have the largest bodies of the three subspecies, and are considered to be in danger of becoming extinct. They are found in mainly sandy or clay environments, although sporadically in sparse woodland areas. Their diet includes tortoises and their eggs, small mammals, along with adult cobras and vipers. They are strong diggers and can easily build burrows that are several feet long. [1]
The Varanus griseus koniecznyi subspecies (Indian Desert Monitor) has 3-5 bands on its back, 13-19 bands on the tail, a plain tail tip, 108-139 rows of scales on their midsection, and a broader and flatter head when compared to the other subspecies. They are mainly found in Pakistan and India, and have the smallest body of the three subspecies. They have been reported to possibly not go through the normal hibernation period over the winter, but are still inactive and do not feed between December and March. Their normal diet consists mainly of invertebrates, but can also branch out to other lizards and small mammals. [1]
The Varanus griseus species goes into hibernation from approximately September all the way to April. In April there is a mass exodus from their hibernation, and they become most active between the months of May through July. During the middle of the day, the lizards mainly stay in their burrows and only come to the desert surface in order to search for food. The monitor lizards require approximately three to four full hibernation periods (years) in order to reach their full size (approximately 55-65 cm excluding their tail) and at least three hibernation periods before they become sexually mature. The overall lifespan of Varanus griseus in the wild does not normally exceed approximately eight years in both males and females. [3]
Varanus griseus is a cold blooded ectotherm whose behaviors therefore depend on the outside temperatures. Many lizards become sluggish in cold weather and even may become inactive if the temperature decreases substantially. Their olfactory and nerve signals significantly slow down which severely limit the lizard from either catching potential prey or escaping from predators. The body temperature of Varanus griseus is directly proportional to its running speed between the temperatures of 21 and 37 degrees Celsius. Between those temperatures the running speed of the monitor lizard increases from a little over 1 meter/second at 21 degrees to approximately 3 meters/second at 37 degrees. Over 37 degrees Celsius its running speed does not increase, and below 21 degrees the lizards are extremely sluggish. If they are being pursued by a predator while their body temperature is less than 21 degrees, they will not flee but will instead hold their ground and become extremely aggressive. The more their body temperature drops, the more aggressive the lizards become. In contrast, they can easily run away from the threat if their body temperature is high enough to allow for rapid movements. The outside temperature does indeed play a big role in their behavior and body functions. [4]
The body temperature of Varanus griseus depends mainly on the outside environment (time of day, season, etc). Their internal temperatures begin warming up before they even leave their burrows through conductive heat gain, and their temperatures rapidly rise once they begin basking in the morning sun and reach their highest point in the noonday heat. The specific body temperature of Varanus griseus can vary depending on the average temperatures of the country they live in, but their maximum body temperature does not usually exceed 38.5 degrees Celsius even when basking in the sunlight. Male monitor lizards are generally more active and also have a higher average body temperature than their female counterparts. The body temperature of the lizards during hibernation is anywhere from 15 to 30.5 degrees Celsius, but in many areas the average body temperature during hibernation is around 16-18 degrees Celsius. [5]
Desert Monitor reproduction normally takes place between the months of May through July. Copulation occurs in May and June and the lizards normally lay their eggs from the latter part of June through the beginning of July. [3] The eggs are incubated at temperatures from 29 to 31 degrees Celsius and hatch after an average of 120 days. At birth, the baby lizards have a total length of around 25 centimeters. [6]
As with the almost every member of the Varanus genus, Varanus griseus is a carnivore. The preferred prey of the species is mice, eggs, or fish, but it will also prey on smaller mammals, reptiles, birds, amphibians, insects, or other invertebrates if the opportunity is presented to them. [7]
The possibility of venom in the Varanus genus is widely debated. It was previously thought that venom was unique to Serpentes (snakes) and Heloderma (venomous lizards). It was believed that the aftereffects of a Varanus bite were due to oral bacteria alone, but recent studies have shown that there are most likely venom glands in the mouth of several, if not all of the species. Varanus griseus has not yet been specifically tested, but its bites have shown consistent aftereffects with the venomous bites from other Varanid lizards. The venom can be used as a defensive mechanism to fend off predators, to help digest food, to sustain oral hygiene, and to possibly help in capturing and killing prey. [7]
Varanus griseus is not threatened in much of its habitat, although much of the land previously inhabited by the subspecies Varanus griseus caspius has been turned into farmland which puts pressure on the species. It is estimated that approximately 17,000 skins of this lizard are involved in commercial trade every year. Trading the skins internationally is prohibited by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). In northern Africa, central Asia, and parts of India however, the species is unprotected from hunting laws and is still hunted commercially. [8]
These lizards rarely do well in captivity, and at most live only a handful of years there. On occasion when their living requirements can be specifically met they have been documented as living for more than 17 years while in captivity, although they never become docile and never become accustomed to being handled. [1] In captivity their environments should mirror those of many ground dwelling animals as well as their natural desert habitat. They require lower temperatures in order to hibernate during the winter along with warmer temperatures during the summer months, and their diet in captivity is similar to their diet in the wild. [6]
Jordan, Turkey (from Urfa) [Eiselt (1970), Böhme (1973)] Morocco, Algeria, Tunisia, Libya, Egypt, Palestine, Israel, Syria, Lebanon, Iraq, Arabia, Oman, Turkmenistan, Kazakhstan, Uzbekistan, Tajikistan, Kyrgyzstan Western Sahara, Mauritania, Mali, Niger, Chad, Sudan, Afghanistan, Iran (including Kavir desert), Pakistan, NW India [1] [6]
Type locality: Dardsha, coast of the Caspian Sea
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