The desert monitor (''Varanus griseus'') is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of monitor lizard of the order

Squamata Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species ...

found living throughout

North Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in ...

and Central and

South Asia South Asia is the southern subregion of Asia, which is defined in both geographical Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth descr ...

. The desert monitor is carnivorous, feeding on a wide range of vertebrates and invertebrates.Bennett, D
‘’Desert Monitor, Grey Monitor’’
''A Little Book of Monitor Lizards'', Viper Press, 1995

Description

Body features

''Varanus griseus'' monitor lizards normally display a variety of body coloration from light brown and yellow to grey. They average about one meter in length, but can reach total body lengths of almost two meters. These lizards can also have horizontal bands on either their backs or tails, along with yellow spots across their backs. Their young are normally a brightly colored orange and have distinctive bands across their backs which may be lost as they mature. Their

nostrils A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...

are slits located farther back on their snouts (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 biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...

in which they shed their outer layer of skin to expand their overall body size. This process can take several months and happens around three times per year. Their skin is adapted to the desert environment where they live, and they are excellent swimmers and divers and have been known to enter the water occasionally to hunt for food.

Subspecies

Three subspecies have been described:Mertens, R, "Über die Rassen des Wüstenwarans (Varanus griseus)", Senckenb. Biol. 1954, 35, 353-357 * ''V. g. griseus'' (grey monitor) * ''V. g. caspius'' (Caspian monitor) * ''V. g. koniecznyi'' (Indian desert monitor)

''Varanus griseus griseus''

The ''V. g. griseus'' subspecies (grey monitor) has five to eight narrow grey bands on its back, as well as 19-28 bands on its tail. Its tail is more rounded that those of the other subspecies, and the final size of the adult depends on which

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

they are living. Their coloration can be from simple grey (in desert-like ecosystems) to brilliantly colored (in areas with large amounts of plant growth). Their most common prey is lizards and snakes, but can also include ground-nesting birds and other small

mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur o ...

''Varanus griseus caspius''

The ''V. g. caspius'' subspecies (Caspian monitor) has five to eight bands on its back, 13-19 bands on its tail, a plain tail tip, and about 143 rows of scales in the middle section of its body. It has the largest body of the three subspecies, and is considered to be in danger of becoming extinct. They are found in mainly sandy or clay environments, although sporadically in sparsely woodland areas. Their diets include

tortoises Tortoises () are reptiles of the family Testudinidae of the order Testudines (Latin: ''tortoise''). Like other turtles, tortoises have a turtle shell, shell to protect from predation and other threats. The shell in tortoises is generally hard, ...

and their eggs, small mammals, and adult cobras and

vipers The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs th ...

. They are strong diggers and can easily build burrows that are several feet long.

''Varanus griseus koniecznyi''

The ''V. g. koniecznyi'' subspecies (Indian desert monitor) has three to five bands on its back, 13-19 bands on its tail, a plain tail tip, 108-139 rows of scales on its midsection, and a broader and flatter head when compared to the other subspecies. It is mainly found in

Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's fifth-most populous country, with a population of almost 243 million people, and has the world's second-lar ...

and

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

, and has the smallest body of the three subspecies. They have been reported to possibly not go through the normal hibernation period over the

winter Winter is the coldest season of the year in polar and temperate climates. It occurs after autumn and before spring. The tilt of Earth's axis causes seasons; winter occurs when a hemisphere is oriented away from the Sun. Different cultur ...

, but are still inactive and do not feed between December and March. Their normal diets consist mainly of

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordat ...

, but can also branch out to other lizards and small mammals.

Lifestyle

''V. griseus'' goes into hibernation from about September to April. In April is a mass exodus from their hibernation, and they become most active between May and July. During the middle of the day, the lizards mainly stay in their burrows and only come to the desert surface to search for food. The monitor lizards require approximately 3 to 4 full hibernation periods (years) to reach their full size (about 55–65 cm excluding their tails) and at least 3 hibernation periods before they become sexually mature. The overall lifespan of ''V. griseus'' in the wild does not normally exceed around 8 years in both males and females.Smirina, E.M., and Tsellarius, A. Yu
''Aging, Longevity, and Growth of the Desert Monitor Lizard''
Russian Journal of Herpetology, Vol. 3 No. 2, pp. 130-142, 1996

Importance of body temperature

''V. griseus'' is a cold-blooded

ectotherm An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life ...

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 Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

or escaping from

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

s. The body temperature of ''V. griseus'' is directly proportional to its running speed between the temperatures of 21 and 37 °C. Between those temperatures, the running speed of the monitor lizard increases from a little over 1 m/s at 21 °C to around 3 m/s at 37 °C. Over 37 °C, its running speed does not increase, and below 21 °C, the lizards are extremely sluggish. If they are being pursued by a

while their body temperature is less than 21 °C, they will not flee, but will instead hold their ground and become extremely aggressive. The body temperature of ''V. 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 ''V. 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 °C even when basking in the sunlight. Male monitor lizards are generally more active and have a higher average body temperature than the females. The body temperature of the lizard during hibernation is 15.0 to 30.5 °C, but in many areas, the average body temperature during hibernation is around 16-18 °C.Ibrahim, Adel A
''A radiotelemetric study of the body temperature of Varanus griseus in Zaranik Protected Area, North Sinai, Egypt''
Egyptian Journal of Biology, Vol. 2, pp.57-66, 2000 The species is one of the few monitor lizards that tolerate relatively cold temperatures, being present as far north as south-west Kazakhstan.

Reproduction

Desert monitor reproduction normally takes place between May and July.

Copulation Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...

occurs in May and June, and the lizards normally lay their eggs from the latter part of June through the beginning of July. The eggs are incubated at temperatures from 29 to 31 °C, and hatch after an average of 120 days. At birth, the baby lizards have a total length of around 25 cm.''Varanus griseus (Daudin 1803) Desert Monitor"

Feeding, hunting, and diet

Like most members of the genus '' Varanus'', ''V. griseus'' is a

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...

. The preferred

of the species is mice,

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

, or fish, but it will also prey on smaller mammals, reptiles, birds, amphibians,

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

s, or other invertebrates, if the opportunity presents itself.Arbuckle, Kevin
''Ecological Function of Venom in ''Varanus'', with a Compilation of Dietary Records from the Literature''
Biowak, Vol. 3(2), pp. 46-56, 2009

Venom

The possibility of

venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a st ...

in the genus ''Varanus'' is widely debated. Previously, venom was thought to be unique to

Serpentes Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints ...

(snakes) and Heloderma (venomous lizards). The aftereffects of a ''Varanus'' bite were thought to be due to oral

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

alone, but recent studies have shown

glands are more likely in the mouths of several, if not all of the species. ''V. griseus'' has not yet been specifically tested, but its bites have shown aftereffects consistent 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 possibly to help in capturing and killing prey.

Conservation

''Varanus griseus'' is not threatened in much of its

, although a great deal of the land previously inhabited by the subspecies ''V. g. caspius'' has been turned into farmland, which puts pressure on the species. Around 17,000 skins of this lizard are involved in commercial trade every year. The species is listed under Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (

CITES CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...

) meaning commercial international trade is prohibited. In northern Africa, central Asia, and parts of India, the species is unprotected from hunting laws and is still hunted commercially.

Captivity

These lizards rarely do well and, at most, live only a few years in captivity. On occasion, when their living requirements can be specifically met, they have been documented to live for more than 17 years, although they never become docile, and never become accustomed to being handled. In captivity, their environments should mirror those of many ground-dwelling animals, as well as their natural desert habitat. They require lower temperatures to hibernate during the winter, along with warmer temperatures during the summer months, and their diets in captivity should be similar to their diets in the wild.

Distribution

Jordan, Turkey (from Urfa) iselt (1970), Böhme (1973)Morocco, Algeria, Tunisia, Libya, Egypt, 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 Type locality: Dardsha, coast of the Caspian Sea Varanus griseus gab fbi

References

External links

Photos of Desert Monitor at Arkive.org

Desert Monitor account at moroccoherps.com

Photos of Desert Monitor
* * Tsellarius, A. Y.;Cherlin, V. A.;Menshikov, Y. A. 1991 Preliminary report on the study of biology of Varanus griseus (Reptilia, Varanidae) in Middle Asia Herpetological Researches (1): 61-103 {{Taxonbar, from=Q838735 Varanus Lizards of Africa Reptiles of Central Asia Fauna of the Sahara Reptiles of India Reptiles of Iran Reptiles of the Middle East Reptiles of Pakistan Reptiles of the Arabian Peninsula Fauna of Turkey Reptiles described in 1803 Taxa named by François Marie Daudin