Desert monitor | |
---|---|
Caspian monitor (Varanus griseus caspius) | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Order: | Squamata |
Family: | Varanidae |
Genus: | Varanus |
Subgenus: | Psammosaurus |
Species: | V. griseus |
Binomial name | |
Varanus griseus (Daudin, 1803) | |
Synonyms | |
|
The desert monitor (Varanus griseus) is a species of monitor lizard of the order Squamata found living throughout North Africa and Central and South Asia. The desert monitor is carnivorous, feeding on a wide range of vertebrates and invertebrates. [3]
Desert monitors 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 coloured orange and have distinctive bands across their backs which may be lost as they mature. Their nostrils 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. Those differences allow males to be distinguished from females. Like all lizards, they go through periods of molting in which they shed their outer layer of skin to expand their overall body size. For adults, 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. [4]
Three subspecies have been described: [5]
V. g. griseus (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 they are living. Their coloration can be from simple grey (in desert-like ecosystems) to bright orange (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. [3]
It can be found in north Africa (from Morocco and Mauritania east to Egypt and Sudan), the Arabian Peninsula (although appearing to be absent from Bahrain), southeastern Turkey, Syria, Israel, Palestine, Lebanon, Jordan and Iraq. [6]
V. g. caspius (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. The Caspian monitor is found from the eastern shore of the Caspian Sea and east to the Central Asian plateaus, as well as islets of the Aral Sea. They can be found at elevations up to 800 meters in the Kopet Dag Mountains, northern Iran, western and southern Afghanistan and as far as south as western Pakistan. It is best-known from the secretions of Turkmenistan, Kazakhstan, Uzbekistan, Kyrgyzstan and Tajikistan.
They are found in barren areas of mainly sand and/or clay soils, and occasionally in wooded areas. Their diets include numerous invertebrates, small lizards and birds, bird eggs, young turtles and tortoises (and their eggs), rodents, and even cobras and vipers. They are strong diggers and can easily build burrows that are several feet long. [3]
V. g. koniecznyi (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. This subspecies has the smallest body of the three. It is mainly found in Pakistan and west-central India, including the states of Gujarat, Rajasthan, Madhya Pradesh and Maharashtra, and probably others.
Due to climatic variations, the Indian subspecies has, reportedly, not been observed engaging in hibernation over the winter, but rather decreasing physical activity, becoming lethargic and inactive. They tend to not feed between December and March. When they resume their normal diets, prey will consist mainly of larger invertebrates and insects, but will also include smaller lizards, rodents, birds, and their chicks and eggs, and various other small vertebrates. [3]
Desert monitors 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 desert monitors in the wild does not normally exceed around 8 years in both males and females. [7]
Desert monitors are cold-blooded ectotherms whose behaviours 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 desert monitors 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 predator while their body temperature is less than 21 °C, they will not flee, but will instead hold their ground and become extremely aggressive.[ citation needed ]
The body temperature of desert monitors depend 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 desert monitors 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. Males 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. [8]
The species is one of the few monitor lizards that tolerate relatively cold temperatures, being present as far north as south-west Kazakhstan. [9]
Desert monitor reproduction normally takes place between May and 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. [7] 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. [10]
Like most monitor lizards, desert monitors are carnivores. The preferred prey of the species is mice, eggs, or fish, but it will also prey on other small mammals (gerbils and young hares), reptiles (other lizards, snakes, and tortoises), birds, amphibians (toads), insects (beetles, orthopterans, heteropteran bugs, and ants), other invertebrates (snails, centipedes, and scorpions), or carrion, if the opportunity presents itself. [11] [12]
Although venom was once thought to be unique to snakes, Gila monsters, and beaded lizards, this is no longer the case. Monitor lizard bite wounds often suffer more than just laceration damage. These aftereffects of monitor bites were once thought to be due to oral bacteria alone, but recent studies have shown that venom glands are in the lower jaws of most if not all species. [13] [14]
Degree of envenomation depends on how long the animal is able to bite down and chew on its target to work venom into the wound. Envenomation appears to induce a neurotoxic effect, causing immediate paralysis in rodents (but not birds). In humans, envenomation from the species causes nausea and vomiting, dizziness, muscle pain of eventually the entire body, accelerated heartbeat, complicated breathing, and diarrhea, with symptoms appearing after as little as 20 minutes, but ending after around 24 hours, although itching of the bite area can potentially persist for 2 months at least. An unusual lack of inflammation has been noted. [15]
Along with assistance in immobilizing prey, the venom contains protease, which is known to cause blood clotting disorders, but also helps to digest food through breaking down proteins. Hyaluronidase within the venom has a similar digestive effect, increasing the production of digestive enzymes. [15]
Desert monitors are not threatened in much of its habitat, 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) 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. [16]
These lizards rarely do well in captivity and at most live only a few years. 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. [3] 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. [10]
The desert monitor has a wide distribution across many countries and regions. It can be found in Jordan, Turkey, Morocco, Algeria, Tunisia, Libya, Egypt, [8] [17] Israel, Syria, Lebanon, Iraq, Oman, Turkmenistan, Kazakhstan, Uzbekistan, Tajikistan, Kyrgyzstan, Western Sahara, Mauritania, Mali, Niger, Chad, Sudan, Afghanistan, Iran (including the Kavir desert), Pakistan, and northwest India. Its type locality is Dardsha, located on the coast of the Caspian Sea. [3] [10]
The Komodo dragon, also known as the Komodo monitor, is a member of the monitor lizard family Varanidae that is endemic to the Indonesian islands of Komodo, Rinca, Flores, and Gili Motang. It is the largest extant species of lizard, growing to a maximum length of 3 m (9.8 ft), and weighing up to 70 kg (150 lb).
Monitor lizards are lizards in the genus Varanus, the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are recognized.
Crotalus cerastes, known as the sidewinder, horned rattlesnake or sidewinder rattlesnake, is a pit viper species belonging to the genus Crotalus, and is found in the desert regions of the Southwestern United States and northwestern Mexico. Like all other pit vipers, it is venomous. Three subspecies are currently recognized.
A goanna is any one of several species of lizard of the genus Varanus found in Australia and Southeast Asia.
The Bengal monitor, also called the Indian monitor, is a monitor lizard distributed widely in the Indian Subcontinent, as well as parts of Southeast Asia and West Asia. This large lizard is mainly a terrestrial animal, and its length ranges from about 61 to 175 cm from the tip of the snout to the end of the tail. Young monitors may be more arboreal, but adults mainly hunt on the ground, preying mainly on arthropods, but also taking small terrestrial vertebrates, ground birds, eggs and fish. Although large Bengal monitors have few predators apart from humans who hunt them for meat, younger individuals are hunted by many predators.
The perentie is a species of monitor lizard. It is one of the largest living lizards on earth, after the Komodo dragon, Asian water monitor, and the Crocodile monitor. Found west of the Great Dividing Range in the arid areas of Australia, it is rarely seen, because of its shyness and the remoteness of much of its range from human habitation. The species is considered to be a least-concern species according to the International Union for Conservation of Nature.
The Mexican beaded lizard is a species of lizard in the family Helodermatidae, one of the two species of venomous beaded lizards found principally in Mexico and southern Guatemala. It and the other members of the same genus, including the Gila monster, are the only lizards known to have evolved an overt venom delivery system. The Mexican beaded lizard is larger than the Gila monster, with duller coloration, black with yellowish bands. As it is a specialized predator that feeds primarily upon eggs, the primary use of its venom is still a source of debate among scientists. This venom has been found to contain several enzymes useful for manufacturing drugs in the treatment of diabetes, and research on the pharmacological use of its venom is ongoing.
The Asian water monitor is a large varanid lizard native to South and Southeast Asia. It is widely considered to be the second-largest lizard species. It is distributed from eastern and northeastern India and Bangladesh, the Andaman and Nicobar Islands, Sri Lanka, through southern China and Hainan Island in the east to mainland Southeast Asia and the islands of Sumatra, Borneo, Java, Lombok, the Riau Archipelago, Sulawesi. It is one of the most widespread monitor lizards.
The lace monitor, also known as the tree goanna, is a member of the monitor lizard family native to eastern Australia. A large lizard, it can reach 2 metres (6.6 ft) in total length and 14 kilograms (31 lb) in weight. The lace monitor is considered to be a least-concern species according to the International Union for Conservation of Nature.
The black tree monitor or Beccari's monitor is a species of lizard in the family Varanidae. The species is a relatively small member of the family, growing to about 90–120 cm (35–47 in) in total length. V. beccarii is endemic to the Aru Islands off New Guinea, living in an arboreal habitat. The skin color of adults is completely black, to which one common name refers.
The western diamondback rattlesnake or Texas diamond-back is a rattlesnake species and member of the viper family, found in the southwestern United States and Mexico. Like all other rattlesnakes and all other vipers, it is venomous. It is likely responsible for the majority of snakebite fatalities in northern Mexico and the greatest number of snakebites in the U.S. No subspecies are currently recognized.
The Indian grey mongoose or Asian grey mongoose is a mongoose species native to the Indian subcontinent and West Asia. It is listed as Least Concern on the IUCN Red List.
The yellow-spotted monitor, also known as the Argus monitor, is a monitor lizard found in northern and western regions of Australia and southern New Guinea.
The spiny-tailed monitor, also known as the Australian spiny-tailed monitor, the ridge-tailed monitor the Ackie dwarf monitor, and colloquially simply ackie monitor, is an Australian species of lizard belonging to the genus of monitor lizards (Varanus).
The Anguimorpha is a suborder of squamates. The group was named by Fürbringer in 1900 to include all autarchoglossans closer to Varanus and Anguis than Scincus. These lizards, along with iguanians and snakes, constitute the proposed "venom clade" Toxicofera of all venomous reptiles.
The Gila monster is a species of venomous lizard native to the Southwestern United States and the northwestern Mexican state of Sonora. It is a heavy, slow-moving reptile, up to 56 centimetres (22 in) long, and it is the only venomous lizard native to the United States. Its venomous close relatives, the four beaded lizards inhabit Mexico and Guatemala. The Gila monster is sluggish in nature, so it is not generally dangerous and very rarely poses a real threat to humans. However, it has a fearsome reputation and is sometimes killed despite the species being protected by state law in Arizona.
The pygmy mulga monitor, also known commonly as Gillen's monitor or just the mulga monitor, is a species of lizard in the family Varanidae. The species is endemic to Australia.
The Rosenberg's monitor is an Australian species of varanid reptile found in southern regions of the continent. They are large and fast predators with rugged bodies and long tails, having a combined length up to 1.5 metres, that will consume any smaller animal that is pursued and captured or found while foraging. They occur in the Australian Capital Territory, New South Wales, South Australia, Victoria, where it may be rare or locally common, and more frequently observed in Western Australia, where it is sometimes abundant.
Hapturosaurus, sometimes known as the tree monitors, is a subgenus of lizards, consisting of slender-bodied arboreal monitor lizards mostly found in the tropical rainforests of Indonesia and Papua New Guinea.