The Asian water monitor has a natural affinity towards water, inhabiting the surroundings of lakes, rivers, ponds, swamps and various riparian habitats, including sewers, city parks, and urban waterways. It is an excellent swimmer and hunts fish, frogs, invertebrates, water birds, and other types of aquatic and amphibious prey. Due to its apparently large, stable population, it is currently listed as Least Concern on to the IUCN Red List.
Etymology
The generic name Varanus is derived from the Arabicwaral (ورل), which translates as "monitor". The specific name is the Latin word for "saviour", denoting a possible religious connotation.[2] The water monitor is occasionally confused with the crocodile monitor (V. salvadorii) because of their similar scientific names.[3]
Some common names for the species are Malayan water monitor, common water monitor, two-banded monitor, rice lizard, ring lizard, plain lizard, no-mark lizard and water monitor etc.
The family Varanidae contains nearly 80 species of monitor lizards, all of which belong to the genus Varanus.[5] There is a significant amount of taxonomic uncertainty within this species complex. Morphological analyses have begun to unravel this taxonomic uncertainty but molecular studies are needed to test and confirm the validity of certain groupings within this genus. Research initiatives such as these are very important to assess changes in conservation assessments.[1]
"V. s. komaini" (melanistic V. s. macromaculatus)V. s. bivittatus(Mertens 1959), the two-striped water monitor, is common to the Indonesian islands of Java, Bali, Lombok, Sumbawa, Flores, Alor, Wetar and some neighbouring islands within the Sunda archipelago. The type locality is Java.[citation needed]
The black water monitor from Thailand's Satun Province and Thai-Malaysian border area was formerly the subspecies V. s. komaini, but now is regarded as a junior synonym and melanistic population of V. s. macromaculatus.[7]
Description
Young water monitorV. s. macromaculatusCloseup showing split tongue
The Asian water monitor is dark brown or blackish with yellow spots on the underside that fade gradually with age. It has blackish bands with yellow edges extending back from each eye. Its body is muscular, with long, powerful, laterally compressed tails. Its scales are keeled; the ones on top of the head are larger than those on the back. Its neck is long and the snout elongated. It has powerful jaws, serrated teeth and sharp claws.[8]
Adults rarely exceed 1.5–2m (4ft 11in– 6ft 7in) in length, but the largest specimen on record from Sri Lanka measured 3.21m (10.5ft). A common mature weight is 19.5kg (43lb).[8] However, 80 males killed for the leather trade in Sumatra averaged only 3.42kg (7.5lb) and 56.6cm (22.3in) snout-to-vent and 142cm (56in) in total length; 42 females averaged 3.52kg (7.8lb) and 59cm (23in) snout–vent length and 149.6cm (58.9in) in total length.[8] Males are larger than females and attain breeding maturity at a length of 40cm (16in) and a weight of 1kg (2.2lb); and females at a length of 50cm (20in).[8]
A series of adults weighed 7.6kg (17lb).[9] Mature individuals in northern Sumatra were estimated to have a mean estimated body mass of 20kg (44lb).[10] A sample of 55 Asian water monitors weighed 2–32kg (4.4–70.5lb).[11] The maximum weight of captive individuals is over 50kg (110lb).[12]
In captivity, Asian water monitors' life expectancy has been determined to be anywhere between 11 and 25 years depending on conditions, in the wild it is considerably shorter.[13][14]
The teeth are compressed, serrated (though irregularly) and recurved. Up to two replacement teeth lie behind each tooth position at a given time, and teeth are replaced every 59 days.[15]
The Asian water monitor is widely distributed from India, Bangladesh, Sri Lanka, Myanmar and Thailand, Cambodia, Laos, Vietnam, the Chinese Guangxi and Hainan provinces, Malaysia, Singapore to the Sunda islandsSumatra, Java, Bali, Borneo and Sulawesi. It inhabits primarily lowland freshwater and brackish wetlands. It has been recorded up to an elevation of 1,800m (5,900ft).[1]
The Asian water monitor is semiaquatic and opportunistic; it inhabits a variety of natural habitats though predominantly resides in primary forests and mangrove swamps. It has been noted that it is not deterred from living in areas near human civilization. In fact, it has been known to adapt and thrive in agricultural areas as well as cities with canal systems, such as in Sri Lanka, where they are not hunted or persecuted. Habitats that are considered to be most important are mangrove vegetation, swamps, wetlands, and elevations below 1,000m (3,300ft). It does not thrive in habitats with extensive loss of natural vegetation and aquatic resources.[1]
A population of these monitors have become established as an invasive population in the southeastern parts of the USA.[16]
Water monitors defend themselves using their tails, claws, and jaws. They are excellent swimmers, using the raised fin on their tails to steer through water. When encountering smaller prey items, the water monitor will subdue it in its jaws and proceed to violently thrash its neck, destroying the prey's organs and spine which leaves it dead or incapacitated. The lizard will then swallow it whole. In dominantly aquatic habitats, their semiaquatic behavior is considered to provide a measure of safety from predators. This along with their versatile diet is said to contribute to their plasticity, or ecological adaptability.[1] When hunted by predators such as the king cobra (Ophiophagus hannah) they will climb trees using their powerful legs and claws. If this evasion is not enough to escape danger, they have also been known to jump from trees into streams for safety, a tactic similar to that of the green iguana (Iguana iguana).[13]
Hatchling V. s. macromaculatus
Juvenile V. s. macromaculatus
Adult V. s. macromaculatus
Like the Komodo dragon, the water monitor will often eat carrion,[2][17] or rotten flesh. By eating this decaying flesh, the lizard provides benefits to the ecosystem by removing infectious elements, cleaning the environment.[18] They have a keen sense of smell and can smell a carcass from far away.
While adults are terrestrial, juveniles are primarily arboreal. [19]
The first description of the water monitor and its behaviour in English literature was made in 1681 by Robert Knox, who observed it during his long confinement in the Kingdom of Kandy: "There is a Creature here called Kobberaguion, resembling an Alligator. The biggest may be five or six feet long, speckled black and white. He lives most upon the Land, but will take the water and dive under it: hath a long blue forked tongue like a sting, which he puts forth and hisseth and gapeth, but doth not bite nor sting, tho the appearance of him would scare those that knew not what he was. He is not afraid of people, but will lie gaping and hissing at them in the way, and will scarce stir out of it. He will come and eat Carrion with the Dogs and Jackals, and will not be scared away by them, but if they come near to bark or snap at him, with his tail, which is long like a whip, he will so slash them, that they will run away and howl."[20]
Reproduction
The Asian water monitor breeds between April and October. The females will lay their eggs about a month after mating in rotting logs or stumps. A clutch can vary from 10 to 40 eggs with an incubation period of 6 to 7 months. When hatched, hatchlings are fully developed and independent. Once males and females reach a length of about 1 meter and 50 centimeters, respectively, they will become reproductively mature and able to breed.[citation needed]
Diet
They are carnivores, and consume a wide range of prey. They are known to eat fish, frogs, rodents, birds, crabs, and snakes.[2] They have also been known to eat turtles, as well as young crocodiles and crocodile eggs.[21] Water monitors have been observed eating catfish in a fashion similar to a mammalian carnivore, tearing off chunks of meat with their sharp teeth while holding it with their front legs and then separating different parts of the fish for sequential consumption.[22] In Java, they have also been recorded entering caves at night to hunt bats that have fallen from cave's ceiling.[23]
V. s. salvator at Kandy Lake (Bogambara lake), Sri Lanka. Possibly obese or gravid, or both.
As carnivores and scavengers,[24] the diet of the Asian water monitor in an urban area in central Thailand includes fish, crabs, Malayan snail-eating turtles (Malayemys macrocephala), Chinese edible frogs (Hoplobatrachus rugulosus), birds, small rodents, domestic cats (Felis catus) and dogs (Canis familiaris), chickens (Gallus gallus domesticus), food scraps and carcass.[25] They are known to feed on dead human bodies. While on the one hand their presence can be helpful in locating a missing person in forensic investigations, on the other hand they can inflict further injuries to the corpse, complicating ascertainment of the cause of death.[26] The stomachs of 20 adult Asian water monitors caught on Redang Island contained mostly human food waste, followed by turtle eggs and hatchlings, crabs and lizard eggs.[27] The monitor does not thrive in these areas, but manage to still live in them. Studies are being conducted in order to understand how these creatures are able to do so in and around human civilization.[28]
In Sri Lanka, human corpses are often scavenged on by V. s. salvator, which can make it hard to identify the deceased, or to run autopsies. For instance, the feeding marks made by a monitor's sharp claws resemble wounds made by bladed weapons.[29] In one case however, the presence of eight dead water monitors near the corpse of a partially scavenged 51 year old man prompted investigation that revealed the possibility that the man died from poisoning after ingesting a bottle of Carbosulfan pesticide, which then poisoned the water monitors that scavenged on his body.[30]
Venom
V. salvator skull.
The possibility of venom in the genus Varanus is widely debated. Previously, venom was thought to be unique to Serpentes (snakes) and Heloderma (venomous lizards). The aftereffects of a Varanus bite were thought to be due to oral bacteria alone, but recent studies have shown venom glands are likely to be present in the mouths of several, if not all, of the species. The venom may 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.[31][32]
Predation
Adult water monitors have very few predators; with the exception of human hunters, only saltwater crocodiles (Crocodylus porosus) are known to target them.[33]
Interaction with humans
V. s. salvator, Sri Lanka
When feeling threatened, Water monitors have been known to attack humans and they should be handled with caution. The bite of a water monitor can inflict a severe injury. Still, Water monitors have been successfully domesticated as pets, and their bites are not known to be fatal. Some pet stores carry them, however some owners have complained when over time their lizard grew far larger than had been anticipated. Generally they have little fear of humans, and neither do they tend to be aggressive towards humans, so long as they do not feel threatened.[citation needed]
In 1999, a 7 year old boy in Pahang was attacked and bitten in the leg while bathing, requiring 18 stitches.[34]
Threats
Skeleton
Monitor lizards are traded globally and are the most common type of lizard to be exported from Southeast Asia, with 8.1 million exported between 1998 and 2007 for the international leather market.[35] Today the majority of the harvesting of feral water monitors occurs in Southeast Asia, in Indonesia, and in peninsular Malaysia.[36] Efforts to breed or farm Water monitors in captivity on a commercial scale have not been widely successful. The Asian water monitor is one of the most exploited varanids; its skin is used for fashion accessories such as shoes, belts and handbags which are shipped globally, with as many as 1.5 million skins traded annually[1] and between 50,000 and 120,000 skins harvested from the wild in peninsular Malaysia.[36] Other uses include a perceived remedy for skin ailments and eczema,[37] novelty food in Indonesia,[38] and a perceived aphrodisiac,[39] and as pets.[40] In India, several tribal communities hunt these monitor lizards for their meat, fat and skin and the eggs are also harvested. They are often considered as pests and their populations are also threatened by habitat loss and habitat fragmentation.[41]
Conservation
Roadway crossing sign, ThailandYoung V. s. macromaculatus. Video clip
In Nepal, it is a protected species under the Wild Animals Protection Act of 2002. In Hong Kong, it is a protected species under Wild Animals Protection Ordinance Cap 170. In Malaysia, this species is one of the most common wild animals, with numbers comparable to the population of macaques there. Although many fall victim to humans via roadkill and animal cruelty, they still thrive in most states of Malaysia, especially in the shrubs of the east coast states such as Pahang and Terengganu as the regulations in Malaysian states differ based on wildlife management authorities.[42] In Thailand, all monitor lizards are protected species.[40] It is still common in large urban areas in Thailand and is frequently seen in Bangkok's canals and parks. Because of this, it is currently listed as Least Concern in the IUCN Red List. These classifications have been made on the basis that this species maintains a geographically wide distribution, can be found in a variety of habitats, adapts to habitats disturbed by humans, and is abundant in portions of its range despite large levels of harvesting.[1]
Loss of habitat and hunting has exterminated water monitors from most of mainland India. In other areas they survive despite being hunted, due in part to the fact that larger ones, including large females that breed large numbers of eggs, have tough skins that are not desirable.[43]
In Sri Lanka, it is protected by local people who value its predation of "crabs that would otherwise undermine the banks of rice fields".[43] It is also protected as it eats venomous snakes.[44]
The Komodo dragon, also known as the Komodo monitor, is a large reptile 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, with the males growing to a maximum length of 3 m (9.8 ft) and weighing up to 150 kg (330 lb).
The Varanidae are a family of lizards in the superfamily Varanoidea and order Anguimorpha. The family, a group of carnivorous and frugivorous lizards, includes the living genus Varanus and a number of extinct genera more closely related to Varanus than to the earless monitor lizard (Lanthanotus). Varanus includes the Komodo dragon, crocodile monitor, savannah monitor, the goannas of Australia and Southeast Asia, and various other species with a similarly distinctive appearance. Their closest living relatives are the earless monitor lizard and Chinese crocodile lizard. The oldest members of the family are known from the Late Cretaceous of Mongolia.
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.
Megalania is an extinct species of giant monitor lizard, part of the megafaunal assemblage that inhabited Australia during the Pleistocene. It is the largest terrestrial lizard known to have existed, but the fragmentary nature of known remains make estimates highly uncertain. Recent studies suggest that most known specimens would have reached around 2–3 m (6.6–9.8 ft) in body length excluding the tail, while some individuals would have been significantly larger.
The Great Nicobar Biosphere Reserve encompasses a large part of the island of Great Nicobar, the largest of the Nicobar Islands in the Indian Union Territory of Andaman and Nicobar Islands. The Nicobars lie in the Bay of Bengal, eastern Indian Ocean, 190 km (120 mi) to the north of the Indonesian island of Sumatra. The reserve has a total core area of approximately 885 km2, surrounded by a 12 km-wide "forest buffer zone". In year 2013 it was included in the list of Man and Biosphere program of UNESCO to promote sustainable development based on local community effort and sound science.
The Bengal monitor, also called the Indian monitor, is a species of monitor lizard distributed widely in the Indian subcontinent, as well as parts of Southeast Asia and West Asia.
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 desert monitor 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.
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 emerald tree monitor or green tree monitor, is a small to medium-sized arboreal monitor lizard. It is known for its unusual coloration, which consists of shades from green to turquoise, topped with dark, transversedorsal banding. This coloration helps camouflage it in its arboreal habitat. Its color also makes the emerald tree monitor highly prized in both the pet trade and zoos alike.
The rock monitor is a species of monitor lizard in the family Varanidae. The species is endemic to Sub-Saharan Africa, where, on average it is the largest lizard found on the continent. It is called leguaan or likkewaan in some areas.
The peacock monitor, also known commonly as Auffenberg's monitor, is a species of small monitor lizard in the family Varanidae. The species, which belongs to the subgenus Odatria, is endemic to Rote Island, Indonesia.
The black rough-necked monitor is a species of monitor lizard found in Southeast Asian countries of Thailand, Burma, and Malaysia. It is also found in Indonesia on Sumatra and islands of the Riau Archipelago It is sometimes known simply as the roughneck monitor. In Thailand is called h̄èā cĥāng.
The Northern Sierra Madre forest monitor, also known by the local names bitatawa, baritatawa, and butikaw, is a large, arboreal, frugivorous lizard of the genus Varanus.
Dumeril's monitor is a species of lizard in the family Varanidae. The species is endemic to Southeast Asia.
The marbled water monitor, also known commonly as the Philippine water monitor, is a large species of monitor lizard in the family Varanidae. The species is endemic to the Philippines.
Varanus spinulosus, the Solomon Island spiny monitor, Isabel monitor, or spiny-neck monitor, is a species of monitor lizard. It is endemic to the Solomon Islands archipelago and is also known from Santa Isabel Island, San Jorge Island and Bourgainville Island.
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.
Philippinosaurus is one of the 11 subgenera of the genus Varanus. The group consists of three frugivorous species endemic to the Philippines.
↑ Laurenti, J. N. (1768). "XC. Stellio salvator". Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena[Medical Treatise, Exhibiting an Emended Synopsis of Reptiles, with Experiments Concerning Venoms and Antidotes for Austrian Reptiles]. Viennae: Joan. Thomae. p.58.
1 2 3 Koch, A. (2007). "Morphological studies on the systematics of South East Asian Water Monitors (Varanus salvator Complex): Nominotypic populations and taxonomic overview". Mertensiella. 16 (109): e80.
1 2 3 4 Shine, R.; Harlow, P. S. & Keogh, J. S. (1996). "Commercial harvesting of giant lizards: The biology of water monitors Varanus salvator in southern Sumatra". Biological Conservation. 77 (2–3): 125–134. Bibcode:1996BCons..77..125S. doi:10.1016/0006-3207(96)00008-0.
↑ Dryden, G. L.; Green, B.; Wikramanayake, E. D. & Dryden, K. G. (1992). "Energy and water turnover in two tropical varanid lizards, Varanus bengalensis and V. salvator". Copeia. 1992 (1): 102–107. doi:10.2307/1446540. JSTOR1446540.
↑ Shine, R.; Harlow, P. S. (1998). "Ecological traits of commercially harvested water monitors, Varanus salvator, in northern Sumatra". Wildlife Research. 25 (4): 437−447. doi:10.1071/WR97118.
↑ Salakij, C.; Salakij, J.; Prihirunkit, K.; Narkkong, N.-A.; Sanyathitiseree, P.; Kranjanapitukkul, K. (2014). "Quantitative and qualitative morphologic, cytochemical, and ultrastructural characteristics of blood cells in captive Asian water monitors". Veterinary Clinical Pathology. 43 (4): 538–546. doi:10.1111/vcp.12183. PMID25123583.
↑ "Varanus salvator". World Association of Zoos and Aquariums. Archived from the original on 30 April 2015. Retrieved 22 August 2012.
↑ Common Water Monitor (Varanus salvator): Ecological Risk Screening Summary. U.S. Fish & Wildlife Service, February 2022.
↑ Rahman, K. M. M.; Rakhimov, I. I.; Khan, M. M. H. (2017). "Activity budgets and dietary investigations of Varanus salvator (Reptilia: Varanidae) in Karamjal ecotourism spot of Bangladesh Sundarbans mangrove forest". Basic and Applied Herpetology. 31: 45–56. doi:10.11160/bah.79.
↑ Stanner, Michael (2020). "A Case of Arboreality in an Adult Water Monitor (Varanus salvator macromaculatus)". BIAWAK. 14 (1&2): 56–57.
↑ Knox, R. (1681). An Historical Relation of the Island of Ceylon in the East Indies: Together With, an Account of the Detaining in Captivity the Author, and Divers, Other Englishmen Now Living There, and of the Author's Miraculous Escape. London: Richard Chiswell.
↑ Whitaker, R. (1981). "Bangladesh – Monitors and turtles". Hamadryad. 6 (3): 7–9.
↑ Khadiejah, S., Abu-Hashim, A.K., Musa, F.H., Abdul-Patah, P., Abdul-Rahman, M.T., Ismail, H.I., Wahab, A., and Razak, N.A. (2020). Management and Trade in Asian Water Monitors (Varnanus salvator) in Peninsular Malaysia. Department of Wildlife and National Parks Peninsular Malaysia (PERHILITAN). 87 pages.
↑ Wirz, P. (1954). Exorcism and the Art of Healing in Ceylon. Leiden: Brill. p.238.
Further reading
Das, I. (1988). "New evidence of the occurrence of water monitor (Varanus salvator) in Meghalaya". Journal of the Bombay Natural History Society. 86: 253–255.
Deraniyagala, P. E. P. (1944). "Four New Races of the Kabaragoya Lizard Varanus salvator". Spolia Zeylanica. 24: 59–62.
Pandav, B. (1993). "A preliminary survey of the water monitor (Varanus salvator) in Bhitarkanika Wildlife Sanctuary, Orissa". Hamadryad. 18: 49–51.
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