Monitor lizard
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 southern United States as an invasive species. About 80 species are recognized.
Monitor lizards have long necks, powerful tails and claws, and well-developed limbs. The adult length of extant species ranges from in some species such as Varanus sparnus, to over in the case of the Komodo dragon, though the extinct megalania may have reached lengths of more than. Most monitor species are terrestrial, but many are also arboreal or semiaquatic. While most monitor lizards are carnivorous, eating smaller reptiles, fish, birds, insects, small mammals, and eggs, a few species also eat fruit and vegetation.
Etymology
The generic name Varanus is derived from the Arabic word ورل waral, from a common Semitic root ouran, waran, warar or waral, meaning "lizard beast".In English, they are known as "monitors" or "monitor lizards". The earlier term "monitory lizard" became rare by about 1920. The name may have been suggested by the occasional habit of varanids to stand on their two hind legs and to appear to "monitor", or perhaps from their supposed habit of "warning people of the approach of venomous animals". But all of these explanations for the name "monitor" postdate Linnaeus giving the scientific name Lacerta monitor to the Nile monitor in 1758, which may have been based on a mistaken idea by Linnaeus that the German word Waran was connected to warnen, leading him to incorrectly Latinize it as monitor.
Austronesian languages spoken across Southeast Asia, where varanids are common, have a large number of slightly related local names for them. They are usually known as biawak, bayawak, binjawak or minjawak or nyambik, or variations thereof. Other names include hokai ; bwo, puo, or soa ; halo ; galuf or kaluf ; batua or butaan ; alu ; hora or ghora ; phut ; and guibang.
In South Asia, they are known as in Meitei, mwpou in Boro, in Marathi, in Tamil and udumbu in Malayalam, in Bhojpuri, gohi in Maithili, in Sinhala as තලගොයා / කබරගොයා, in Telugu as uḍumu, in Kannada as , in Punjabi and Magahi as goh, in Assamese as gui xaap, in Odia as godhi, and in Bengali as or , as goh in Hindi, and godhā in Sanskrit.
The West African Nile monitor is known by several names in Yoruba, including,, and. In Serer and amongst the Wolofized Serers of Kaolack, it is known as mbossé or bar in Wolof. Mbossé is the tutelary and traditional totem of the city of Kaolack,. The mbossé is also one of the totems of the noble Joof family born of Guelwar matrilineage, which is one of the many Serer maternal clans. The mbossé or mbosseh is one of the Serer religious festivals, and should not be confused with the mythical and sacred tree mbos―enshrined in Serer religion and Serer cosmogony―where the mbossé takes its name.
Due to confusion with the large New World lizards of the family Iguanidae, the lizards became known as "goannas" in Australia. Similarly, in South African English, they are referred to as leguaans, or likkewaans, from the Dutch term for the Iguanidae, leguanen.
Distribution
The various species cover a vast area, occurring through Africa, the Indian subcontinent, to China, the Ryukyu Islands in southern Japan, south to Southeast Asia to Thailand, Malaysia, Brunei, Indonesia, the Philippines, New Guinea, Australia, and islands of the Indian Ocean and the South China Sea. They have also been introduced outside of their natural range, for instance, the West African Nile monitor is now found in South Florida. Monitor lizards also occurred widely in Europe in the Neogene, with the last known remains in the region dating to the Middle Pleistocene.Habits and diet
Most monitor lizards are almost entirely carnivorous, consuming prey as varied as insects, crustaceans, arachnids, myriapods, molluscs, fish, amphibians, reptiles, birds, and mammals. Most species feed on invertebrates as juveniles and shift to feeding on vertebrates as adults. Deer make up about 50% of the diet of adult Komodo dragons, the largest monitor species. In contrast, three arboreal species from the Philippines, Varanus bitatawa, V. mabitang, and V. olivaceus, are primarily fruit eaters.Biology
Monitor lizards are considered unique among animals in that its members are relatively morphologically conservative, yet show a very large size range. However, finer morphological features such as the shape of the skull and limbs do vary, and are strongly related to the ecology of each species.Like snakes, monitor lizards have highly forked tongues that act as part of the "smell" sense, where the tips of the tongue carry molecules from the environment to the a sensory organ in the skull called the Jacobson's organ. The forked apparatus allows for these lizards to sense boundaries in the molecules they collect, almost smelling in "stereo". While most reptiles possess taste buds, monitor lizards and likely snakes as well completely lack taste buds. Merten's water monitor, the most aquatically adapted monitor species, is uniquely capable of using its sense of smell underwater to locate and capture prey.
Monitor lizards are oviparous, laying from seven to 38 eggs, which they often cover with soil or protect in a hollow tree stump. Some species, including the Komodo dragon, are capable of parthenogenesis.
Venom
Anatomical and molecular studies indicate that most if not all varanids are venomous. Unlike snakes, monitor lizard venom glands are situated in their lower jaw. The venom of monitor lizards is diverse and complex, as a result of the diverse ecological niches monitor lizards occupy.For example, many species have anticoagulant venom, disrupting clotting through a combination of fibrinogenolysis and blocking platelet aggregation. Amongst them, arboreal species, such as the tree monitors and the banded monitor, have by far the strongest fibrinogenolytic venom. As a result, wounds from monitor lizard bites often bleed more than they would if they were simply lacerations. Venom may also cause hypotension.
In some species such as the Komodo dragon and the desert monitor, venom also induces a powerful neurotoxic effect. In the latter species for instance, envenomation causes immediate paralysis in rodents and lesser effects of the same nature in humans.
Metabolism
Monitor lizards maintain large territories and employ active-pursuit hunting techniques that are reminiscent of similar-sized mammals. The highly active nature of monitor lizards has led to numerous studies on the metabolic capacities of these lizards. The general consensus is that monitor lizards have the highest standard metabolic rates of all extant reptiles.Monitor lizards have a high aerobic scope that is afforded, in part, by their heart anatomy. Whereas most reptiles are considered to have three-chambered hearts, the hearts of monitor lizards – as with those of boas and pythons – have a well developed ventricular septum that completely separates the pulmonary and systemic sides of the circulatory system during systole. This allows monitor lizards to create mammalian-equivalent pressure differentials between the pulmonary and systemic circuits, which in turn ensure that oxygenated blood is quickly distributed to the body without also flooding the lungs with high-pressure blood.
Intelligence
At least some species of monitors are known to be able to count; studies feeding rock monitors varying numbers of snails showed that they can distinguish numbers up to six. Nile monitors have been observed to cooperate when foraging; one animal lures the female crocodile away from her nest, while the other opens the nest to feed on the eggs. The decoy then returns to also feed on the eggs. Komodo dragons at the National Zoo in Washington, DC, recognize their keepers and seem to have distinct personalities. Blue and green tree monitors in British zoos have been observed shredding leaves, apparently as a form of play.Human uses
As pets
Monitor lizards have become a staple in the reptile pet trade. The most commonly kept monitors are the savannah monitor and Ackie dwarf monitor, due to their relatively small size, low cost, and relatively calm dispositions with regular handling. Among others, black-throated, Timor, Asian water, Nile, mangrove, emerald tree, black tree, roughneck, Dumeril's, peach-throated, crocodile, and Argus monitors have been kept in captivity.Traditional medicines
Monitor lizards are poached in some South- and Southeast Asian countries, as their organs and fat are used in some traditional medicines, although there is no scientific evidence as to their effectiveness.The dried and dyed hemipenes of Bengal monitors, and less often yellow and water monitors, are frequently trafficked and illegally sold in India and online under the deceptive term 'Hatha Jodi', where it is claimed to be the root of a supposed rare Himalayan plant in order to fool buyers and retailers, and to disguise the trade from wildlife authorities. Sellers advertise 'Hatha Jodi' as having the tantric power to bring wealth, power and contentment. A pair of hemipenes may sell at a value of up to US$250. In India, the body oil of monitor lizards is sold for thousands of Indian rupees to residents in metropolitan cities as a treatment for rheumatism.
Monitor lizard meat, particularly the tongue and liver, is eaten in parts of India and Malaysia and is supposed to be an aphrodisiac.
Consuming raw blood and flesh of monitor lizards has been reported to cause eosinophilic meningoencephalitis, as some monitors are hosts for the parasitic nematode Angiostrongylus cantonensis.