Asian water monitor
CITES Appendix II (CITES)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Family: Varanidae
Genus: Varanus
Subgenus: Soterosaurus
Species:
V. salvator
Binomial name
Varanus salvator
(Laurenti, 1768)

The Asian water monitor (Varanus salvator) is a large varanid lizard native to South and Southeast Asia. It is one of the most common monitor lizards in Asia, ranging from coastal northeast India, Bangladesh, Sri Lanka, mainland Southeast Asia, and southern China to Indonesian islands where it lives close to water. It is listed as Least Concern on the IUCN Red List.[1] It was described by Laurenti in 1768 and is among the largest squamates in the world.[2]

Etymology

The generic name Varanus is derived from the Arabic waral (ورل), which translates as "monitor". The specific name is the Latin word for "saviour", denoting a possible religious connotation.[3] The water monitor is occasionally confused with the crocodile monitor (V. salvadorii) because of their similar scientific names.[4]

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.

Taxonomy

Stellio salvator was the scientific name used by Josephus Nicolaus Laurenti in 1768 for a water monitor specimen.[5]

The family Varanidae contains nearly 80 species of monitor lizards, all of which belong to the genus Varanus.[6] 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]

Subspecies

V. s. salvator
  • V. s. salvator is the nominate subspecies and is now restricted to Sri Lanka, where it is known as the kabaragoya (කබරගොයා) in Sinhala and kalawathan in Tamil.
  • V. s. andamanensis, the Andaman Islands water monitor, inhabits the Andaman Islands and the Southern Nicobar Islands.;[7] the type locality is Port Blair.
  • V. s. bivittatus (Mertens 1959), the two-striped water monitor, is common to Java, Bali, Lombok, Sumbawa, Flores, Alor, Wetar, and some neighbouring islands within the Sunda archipelago in Indonesia; the type locality is Java.
  • V. s. macromaculatus, the Southeast Asian water monitor, is found in mainland Southeast Asia, Singapore, Sumatra, Borneo, and smaller associated offshore islands. The type specimen was captured in Thailand.[2][7]
  • V. s. ziegleri, Ziegler's water monitor, is from Obi Island.
Melanistic V. s. macromaculatus

Varanus cumingi, Varanus marmoratus, and Varanus nuchalis were classified as subspecies until 2007, when they were elevated to full species.[2][8]

The black water monitor from Thailand (type locality: Amphoe La-ngu, 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.[2]

Description

Head closeup showing split tongue
Walking on pavement

The water monitor is a large species of monitor lizard. Breeding maturity is attained for males when they are a relatively modest 40 cm (16 in) long and weigh 1 kg (2.2 lb), and for females at 50 cm (20 in). However, they grow much larger throughout life, with males being larger than females.[9] Adults rarely exceed 1.5–2 m (4 ft 11 in – 6 ft 7 in) in length,[10] but the largest specimen on record, from Sri Lanka, measured 3.21 m (10.5 ft). A common mature weight of V. salvator can be 19.5 kg (43 lb).[9][11] However, 80 males killed for the leather trade in Sumatra averaged only 3.42 kg (7.5 lb) and 56.6 cm (22.3 in) snout-to-vent and 142 cm (56 in) in total length; 42 females averaged only 3.52 kg (7.8 lb) and 59 cm (23 in) snout-to-vent and 149.6 cm (58.9 in) in total length,[9] although unskinned outsized specimens weighed 16 to 20 kg (35 to 44 lb).

Another study from the same area by the same authors similarly estimated mean body mass for mature specimens at 20 kg (44 lb)[12] while yet another study found a series of adults to weigh 7.6 kg (17 lb).[13] A sample of 55 Asian water monitors found them in the weight range of 2 to 32 kg (4.4 to 70.5 lb).[14] The maximum weight of the species is over 50 kg (110 lb).[15] In exceptional cases, the species has been reported to reach 75 to 90 kg (165 to 198 lb), though most such reports are unverified and may be unreliable.

They are the world's second-heaviest lizard, after the Komodo dragon.[9] Their bodies are muscular, with long, powerful, laterally compressed tails. The scales in this species are keeled; scales found on top of the head have been noted to be larger than those located on the back. Water monitors are often defined by their dark brown or blackish coloration with yellow spots found on their underside - these yellow markings have a tendency to disappear gradually with age. This species is also denoted by the blackish band with yellow edges extending back from each eye. These monitors have very long necks and an elongated snout. They use their powerful jaws, serrated teeth and sharp claws for both predation and defense.

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.[16][17]

Distribution and habitat

An Asian water monitor in Sunderbans National Park

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 islands Sumatra, Java, Bali, Borneo and Sulawesi. It inhabits primarily lowland freshwater and brackish wetlands. It has been recorded up to an elevation of 1,800 m (5,900 ft).[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 of human disturbance. 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 1,000 m (3,300 ft). It does not thrive in habitats with extensive loss of natural vegetation and aquatic resources.[1]

Behaviour and ecology

Water monitors robbing eggs from a nest. Illustration by Pierre Jacques Smit from Richard Lydekker's The Royal Natural History, 1893–1896
Asian water monitor resting on a rubber tire
Hatchling
Juvenile

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. Paired with their generalist diet, this is thought to contribute to their ecological plasticity.[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).[16]

Like the Komodo dragon, the water monitor will often eat carrion.[3][18] They have a keen sense of smell and can smell a carcass from far away. 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.[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]

Water monitors are prone to attacking humans when threatened, and should be handled with caution. The bite of a water monitor can inflict a severe injury.

Diet

Asian water monitor at Kandy Lake (Bogambara lake), Sri Lanka. Possibly obese or gravid, or both.

They are carnivores, and consume a wide range of prey. They are known to eat fish, frogs, rodents, birds, crabs, and snakes.[3] 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]

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.[23] 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.[24]

Venom

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.[25][26]

Predation

Adult water monitors have few natural predators, and are only known to be preyed on by saltwater crocodiles (Crocodylus porosus).[27]

Threats

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.[28] 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] Other uses include a perceived remedy for skin ailments and eczema,[29] novelty food in Indonesia,[30] and a perceived aphrodisiac,[31] and as pets.[32] 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.[33]

Conservation

Roadway crossing sign, Thailand

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. In Thailand, all monitor lizards are protected species.[32] 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.[34]

In Sri Lanka, it is protected by local people who value its predation of "crabs that would otherwise undermine the banks of rice fields".[34] It is also protected as it eats venomous snakes.[35]

The species is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES) meaning international trade (import/export) in specimens (including parts and derivatives) is regulated.[1]

Asian water monitor - Varanus salvator

References

  1. 1 2 3 4 5 6 7 8 9 10 Quah, E.; Lwin, K.; Cota, M.; Grismer, L.; Neang, T.; Wogan, G.; McGuire, J.; Wang, L.; Rao, D.-Q.; Auliya, M. & Koch, A. (2021). "Varanus salvator". IUCN Red List of Threatened Species. 2021: e.T178214A113138439. doi:10.2305/IUCN.UK.2021-2.RLTS.T178214A113138439.en. Retrieved 29 January 2022.
  2. 1 2 3 4 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.
  3. 1 2 3 Sprackland, R. G. (1992). Giant lizards. Neptune, NJ: T.F.H. Publications. ISBN 978-0-86622-634-9.
  4. ↑ Netherton, J.; Badger, D. P. (2002). Lizards: A Natural History of Some Uncommon Creatures—Extraordinary Chameleons, Iguanas, Geckos, and More. Stillwater, MN: Voyageur Press. pp. 140–141. ISBN 978-0-7603-2579-7.
  5. ↑ 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.
  6. ↑ Böhme, W. (2003). "Checklist of the living monitor lizards of the world (family Varanidae)". Zoologische Verhandelingen, Leiden. 341: 4–43. Archived from the original on 2017-12-22. Retrieved 2020-05-13.
  7. 1 2 Samarasinghe, D. J. S.; Surendran, H.; Koch, A. (2020). "On the taxonomy and distribution of Varanus salvator andamanensis Deraniyagala, 1944 (Reptilia: Varanidae), including a redescription of the type specimens and a discussion about its allopatric co-occurrence with V. s. macromaculatus on the Nicobar Islands". Zootaxa. 4743 (1): 64. doi:10.11646/zootaxa.4743.1.5. PMID 32230352. S2CID 214484186. Archived from the original on 2020-12-22. Retrieved 2020-05-13.
  8. ↑ "Soterosaurus: Mindanao Water Monitor". monitor-lizards.net. Archived from the original on 31 July 2012. Retrieved 20 March 2012.
  9. 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. doi:10.1016/0006-3207(96)00008-0.
  10. ↑ Pianka, King & king. Varanoid lizards of the world. 2004
  11. ↑ Water Monitor Lizard (Varanus salvator) at Pak Lah’s House | Mutakhir Archived 2012-08-27 at the Wayback Machine. Wildlife.gov.my (2012-02-23). Retrieved on 2012-08-22.
  12. ↑ 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.
  13. ↑ 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. JSTOR 1446540.
  14. ↑ Salakij, Chaleow; Salakij, Jarernsak; Prihirunkit, Kreangsak; Narkkong, Naul-Anong; Sanyathitiseree, Pornchai; Kranjanapitukkul, Kwanjai (December 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. PMID 25123583. Archived from the original on 2022-12-25. Retrieved 2022-12-25.
  15. ↑ "Varanus salvator". World Association of Zoos and Aquariums. Archived from the original on 30 April 2015. Retrieved 22 August 2012.
  16. 1 2 "Asian Water Monitor". Wildlife Facts. Archived from the original on 2019-11-11. Retrieved 2017-12-01.
  17. ↑ "Water Monitor Care Sheet | Black Dragon Care Sheet | Varanus salvator Care Sheet". Vital Exotics. Archived from the original on 2 December 2017. Retrieved 1 December 2017.
  18. ↑ 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.
  19. ↑ Gunethilake, K. M. T. B.; Vidanapathirana, M. (2016). "Water monitors; Implications in forensic death investigations". Medico-Legal Journal of Sri Lanka. 4 (2): 48–52. doi:10.4038/mljsl.v4i2.7338.
  20. ↑ 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.
  21. ↑ Whitaker, R. (1981). "Bangladesh – Monitors and turtles". Hamadryad. 6 (3): 7–9.
  22. ↑ Stanner, M. (2010). "Mammal-like Feeding Behavior of Varanus salvator and its Conservational Implications" (PDF). Biawak. 4 (4): 128–131. Archived (PDF) from the original on 2019-04-23. Retrieved 2012-08-21.
  23. ↑ Kulabtong, S. & Mahaprom, R. (2014). "Observation on food items of Asian water monitor, Varanus salvator (Laurenti, 1768) (Squamata Varanidae), in urban eco-system, Central Thailand" (PDF). Biodiversity Journal. 6 (3): 695–698. Archived (PDF) from the original on 2021-05-09. Retrieved 2021-05-02.
  24. ↑ Rusil, M.U.; Chen, G.N.; Booth, D.T. & Lei, J. (2020). "Diet preference and activity of Asian water monitor at Chagar Hutang Turtle Sanctuary" (PDF). Journal of Sustainability Science and Management. 15 (6): 68–74. doi:10.46754/jssm.2020.08.00 (inactive 1 August 2023). Archived (PDF) from the original on 2 May 2021. Retrieved 2 May 2021.{{cite journal}}: CS1 maint: DOI inactive as of August 2023 (link)
  25. ↑ Arbuckle, Kevin (2009). "Ecological Function of Venom in Varanus, with a Compilation of Dietary Records from the Literature" (PDF). Biowak. 3 (2): 46−56. Archived (PDF) from the original on 2018-11-22. Retrieved 2017-08-15.
  26. ↑ Yong, E. (2013). "The Myth of the Komodo Dragon's Dirty Mouth". National Geographic. Archived from the original on 15 August 2017. Retrieved 15 August 2017.
  27. ↑ Ng, M.; Mendyk, R.W. (2012). "Predation of an adult Malaysian Water monitor Varanus salvator macromaculatus by an Estuarine Crocodile Crocodylus porosus" (PDF). Biawak. 6 (1): 34–38. Archived (PDF) from the original on 2020-07-13. Retrieved 2020-04-15.
  28. ↑ Nijman, V. (2010). "An overview of international wildlife trade from Southeast Asia". Biodiversity and Conservation. 19 (4): 1101−1114. doi:10.1007/s10531-009-9758-4. Archived from the original on 2020-12-22. Retrieved 2017-02-02.
  29. ↑ Uyeda, L.; Iskandar, E.; Purbatrapsila, A.; Pamungkas, J.; Wirsing, A.; Kyes, R. (2014). "Water Monitor Lizard (Varanus salvator) Satay: A Treatment for Skin Ailments in Muarabinuangeun and Cisiih, Indonesia". Biawak. 8 (1): 35–38. Archived from the original on 2020-12-22. Retrieved 2019-07-08.
  30. ↑ Nijman, V. (2015). "Water Monitor Lizards for Sale as Novelty Food in Java, Indonesia". Biawak. 9 (1): 28−32. Archived from the original on 2020-12-22. Retrieved 2019-03-13.
  31. ↑ Nijman, V. (2016). "Perceptions of Sundanese Men Towards the Consumption of Water Monitor Lizard Meat in West Java, Indonesia". Biawak. 10 (1): 22−25. Archived from the original on 2020-12-22. Retrieved 2017-02-15.
  32. 1 2 Komsorn L. & Kumthorn Thirakhupt (2001). "Species Diversity, Distribution and Proposed Status of Monitor Lizards (Family Varanidae) in Southern Thailand" (PDF). The Natural History Journal of Chulalongkorn University. 1 (1): 39–46. Archived from the original (PDF) on 2016-03-04. Retrieved 2015-01-26.
  33. ↑ Shreya Bhattacharya; Andre Koch (August 2018). "Effects of Traditional Beliefs leading to Conservation of Water Monitor Lizards (Varanus salvator) and threatened Marshlands in West Bengal, India". Herpetological Conservation and Biology. 13 (2): 408–414 – via ResearchGate.
  34. 1 2 Ria Tan (2001). "Mangrove and wetland wildlife at Sungei Buloh Wetlands Reserve: Malayan Water Monitor Lizard". Naturia.per.sg. Archived from the original on 2019-01-05. Retrieved 2015-09-15.
  35. ↑ 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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