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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: Common Water Monitor

Synonyms and Other Names: biawak, Asian water monitor

Taxonomy: available through www.itis.gov

Identification: A very large lizard that may reach a total length of 2.5 m (exceeding 8 ft) (Minton and Minton, 1973; [Whitaker], 1986; De Lisle, 1996). Adult dorsal coloration is a dark olive with irregular pale, or yellow, spots that may be in transverse rows; often becoming indistinct as the animal ages (De Lisle, 1996; Steel, 1996; Rogner, 1997; Cox et al., 1998). Laterally compressed tail may be banded (De Lisle, 1996). The neck is typically longer than the tapered head. No other lizard indigenous to the U.S. reaches this large size or has this combination of anatomical features. Varanus salvator is illustrated in Smith (1935), Sprackland (1992), De Lisle (1996), Inger and Tan Fui Lian (1996), Steel (1996), Rogner (1997), Bennett (1998), Cox et al. (1998), Cota et al. (2009), and Krysko et al. (2011: MorphoBank Project No. p536, www.morphobank.org).

Size: Can reach a total length of 2.5 m (exceeding 8 ft).

Native Range: Throughout most of Southeast Asia, including Malaysia, Indonesia and its surrounding islands, eastern India, Sri Lanka, the Nicobar Islands, the Philippines, and southernmost China, including Hong Kong (Pope, 1935; Smith, 1935; Daniel, 1983; [Whitaker], 1986; Zhao and Adler, 1993; De Lisle, 1996; Inger and Tan Fui Lian, 1996; Manthey and Grossmann, 1997; Rogner, 1997; Bennett, 1998; Cox et al., 1998; Das, 1999; Cota et al., 2009).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: The most extensive information on the natural history of these massive lizards is provided by Horn (1994), Shine et al. (1996), Bennett (1998), Gaulke and Horn (2004), Horn and Gaulke (2004), and Pianka (2004). Auffenberg (1994) provides additional information in comparing the ecology of V. salvator with V. bengalensis. The water monitor is a tropical, semiaquatic, omnicarnivorous predator that forages on land and in the water, preying upon invertebrates, carrion, human corpses and feces, and any vertebrate (including fish) it can overpower (Smith, 1935; Daniel, 1983, 2002; De Lisle, 1996; Shine et al., 1996; Steel, 1996; Manthey and Grossmann, 1997; Bennett, 1998; Cox et al., 1998).

They typically shelter in large burrows (Bennett, 1998). The female lays her eggs and buries them in a sheltered locality, such as termitaria (termite mounds), hollow logs, or riverbanks (van der Meer Mohr, 1930; Smith, 1935; [Whitaker], 1986; De Lisle, 1996; Manthey and Grossmann, 1997; Wicker et al., 1999; Gaulke and Horn, 2004; Horn and Gaulke, 2004). Several authors have observed maternal parental care, including nest guarding, in various subspecies and populations of V. salvator (Anonymous, 1978; Biswas and Kar, 1981; Wicker et al., 1999; Somma, 2003; Horn and Gaulke, 2004).

Means of Introduction: Unknown for Arizona. Probable pet escapees. Individuals from California are probably released or escaped pets (Kraus, 2009). Varanus salvator found in Florida are escaped or released pets (Krysko et al., 2011). Specimens from Taiwan are thought to be escapees from cargo ships (Zhao and Adler, 1993).

Status: Not established anywhere in the U.S. (Kraus, 2009; Krysko et al., 2011). Varanus salvator is not established in Taiwan (Kraus, 2009).

Impact of Introduction: None in the U.S. Unknown in Taiwan. The potential impact of these huge, aggressive predators on indigenous wildlife almost certainly would be negative should they establish themselves. Moreover, their size and aggressive behavior makes them potentially dangerous to humans.

Remarks: The most extensive information on the natural history of these massive lizards is provided by Shine et al. (1996) and Bennett (1998), with additional information by Stanner (2010) and Cota (2011a, b). Auffenberg (1994) provides additional information in comparing the ecology of V. salvator with V. bengalensis. The water monitor is a tropical, semiaquatic, omnicarnivorous predator that forages on land and in the water, preying upon invertebrates, carrion, human corpses and feces, and any vertebrate (including fish) it can overpower (Smith, 1935; Daniel, 1983; De Lisle, 1996; Shine et al., 1996; Steel, 1996; Manthey and Grossmann, 1997; Bennett, 1998; Cox et al., 1998; Stanner, 2010; Cota, 2011a). They typically shelter in large burrows, sometimes with an underwater entrance (Bennett, 1998; Cota, 2011b). The female lays her eggs and buries them in a sheltered locality, such as termitaria (termite mounds), hollow logs, or river banks (van der Meer Mohr, 1930; Smith, 1935; [Whitaker], 1986; De Lisle, 1996; Manthey and Grossmann, 1997). Biswas and Kar (1981) observed a maternal V. salvator remaining near her nest for several days but were uncertain if any parental care was provided.

While this could be the easiest varanid (monitor) to obtain through the pet trade (Sprackland, 1992; Bennett, 1998), Rogner (1997) recommends that these huge, aggressive lizards only be kept in zoos. Unfortunately, monitor lizards as pet releases/escapees probably represent an increasingly common problem in Florida (Frank and McCoy, 1995; Simberloff, 1997; Krysko et al., 2011). Water monitors are much exploited for their skin and meat (Shine et al., 1996; Rogner, 1997). Under C.I.T.E.S., V. salvator is listed under Appendix II; international trade is regulated through mandatory permits (Level, 1997).

References: (click for full references)

Anonymous. 1999. Cops defend shooting of monitor lizard in DeLand. The League of the Florida Herpetological Societies Newsletter 1990(July):26.

Auffenberg, W. 1994. The Bengal Monitor. University Press of Florida, Gainesville. 560 pp.

Belleville, W. 1994. Critter patrol. The Orlando Sentinel (149; 29 May); Florida [news magazine insert] 41(22):8-12, 15.

Beltz, E. 1992. Herp news from around the world. Maybe it was an emissions monitor. Vivarium 4(2):6.

Bennett, D. 1998. Monitor Lizards. Natural History, Biology & Husbandry. Edition Chimaira (Andreas S. Brahm), Frankfurt am Main. 352 pp.

Biswas, S., and S. Kar. 1981. Some observations on nesting habits and biology of Varanus salvator (Laurenti) of Bhitarkanika Sanctuary, Orissa. Journal of the Bombay Natural History Society 78:303-308.

Cota, M. 2011a. Mating and intraspecific behavior of Varanus salvator macromaculatus in an urban population. Biawak 5(1/2):17-23.

Cota, M. 2011b. Burrows with submerged and water-filled entrances and nocturnal retirement of Varanus salvator macromaculatus in Thailand. Biawak 5(3):44-47.

Cota, M., T. Chan-Ard, and S. Makchai. 2009. Geographical distribution and regional variation of Varanus salvator macromaculatus in Thailand. Biawak 3(4):134-143.

Cox, M. J., P. P. van Dijk, J. Nabhitabhata, and K. Thirakhupt. 1998. A Photographic Guide to Snakes and Other Reptiles of Peninsular Malaysia, Singapore and Thailand. New Holland Publishers (UK) Ltd, London. 144 pp.

Daniel, J. C. 1983. The Book of Indian Reptiles. Bombay Natural History Society, Bombay. 141 pp.

Das, I. 1999. Biogeography of the amphibians and reptiles of the Andaman and Nicobar Islands, India. Pp. 43-77. In: H. Ota (editor). Tropical Island Herpetofauna. Origin, Current Diversity, and Conservation. Elsevier Science B.V., Amsterdam. 353 pp.

De Lisle, H. F. 1996. The Natural History of Monitor Lizards. Krieger Publishing Company, Malabar, Florida. 201 pp.

Demlong, M. 1997. Personal communication—Herpetologist, Phoenix Zoo, 455 N. Galvin Parkway, Phoenix, Arizona.

Frank, J. H., and E. D. McCoy. 1995. Introduction to insect behavioral ecology: The good, the bad, and the beautiful: Non-indigenous species in Florida. Invasive adventive insects and other organisms in Florida. Florida Entomologist 78(1):1-15.

Inger, R. F., and Tan Fui Lian. 1996. The Natural History of Amphibians and Reptiles in Sabah. Natural History Publications (Borneo) Sdn. Bhd., Kota Kinabalu, Malaysia. 101 pp.

Kraus, F. 2009. Alien Reptiles and Amphibians. A Scientific Compendium and Analysis. Springer, [Dordrecht]. 563 pp. + CD-ROM.

Krysko, K. L., J. P. Burgess, M. R. Rochford, C. R. Gillette, D. Cueva, K. M. Enge, L. A. Somma, J. L. Stabile, D. C. Smith, J. A. Wasilewski, G. N. Kieckhefer III, M. C. Granatosky,  and S. V. Nielsen. 2011. Verified non-indigenous amphibians and reptiles in Florida from 1863 through 2010: Outlining the invasion process and identifying invasion  pathways and status. Zootaxa 3028:1-64 + MorphoBank Project No. p536: URL: http://www.morphobank.org.

Krysko, K. L., K. M. Enge, E. M. Donlan, E. A. Golden, J. P. Burgess, and K. W. Larsen. 2010. The non-marine herpetofauna of Key Biscayne, Florida. Herpetological Conservation and Biology 5(5):132–142.

Lemm, J. M. 2006. Field Guide to Amphibians and Reptiles of the San Diego Region. University of California Press, Berkeley. 326 pp.

Level, J. P. 1997. A Field Guide to Reptiles and the Law. Second Revised Edition. Serpent’s Tale Natural History Book Distributors, Lanesboro, Minnesota. 270 pp.

Manthey, U., and W. Grossmann. 1997. Amphibien & Reptilien Südostasiens. Natur und Tier – Verlag, Münster. 512 pp.

Minton, S. A., Jr., and M. R. Minton. 1973. Giant Reptiles. Charles Scribner’s Sons, New York. 345 pp.

Pope, C. H. 1935. The Reptiles of China. Turtles, Crocodilians, Snakes, Lizards. Natural History of Central Asia Vol. X. The American Museum of Natural History, New York. 604 pp. + 27 plates.

Rogner, M. 1997. Lizards. Vol. 2. English Edition. Krieger Publishing Company, Malabar, Florida. 308 pp.

Shine, R., P. S. Harlow, and J. S. Keogh. 1996. Commercial harvesting of giant lizards: The biology of water monitors in southern Sumatra. Biological Conservation 77:125-134.

Simberloff, D. 1997. The biology of invasions. Pp. 3-17. In: D. Simberloff, D. C. Schmitz, and T. C. Brown (editors). Strangers in Paradise. Impact and Management of Nonindigenous Species in Florida. Island Press, Washington, D. C. 467 pp.

Smith, M. A. 1935. The Fauna of British India, Including Ceylon and Burma. Reptilia and Amphibia. Vol. II.—Sauria. Taylor & Francis Ltd., London. 444 pp. + 1 plate.

Sprackland, R. G. 1992. Giant Lizards. T.F.H. Publications, Inc., Neptune City, New Jersey. 288 pp.

Stanner, M. 2010. Mammal-like feeding behavior of Varanus salvator and its conservation implications. Biawak 4(4):128-131.

Steel, R. 1996. Living Dragons. A Natural History of the World’s Monitor Lizards. Blandford, London. 160 pp.

van der Meer Mohr, J. C. 1930. Over eieren van Varanus salvator en van Python curtus. De Tropische Natuur (Weltevreden, Nedlandsch-Indische) 19(9):156-157.

[Whitaker, R.] 1986. Monitor lizards. Pp. 378-379. In: R. E. Hawkins (editor). Encyclopedia of Indian Natural History. Oxford University Press on behalf of the Bombay Natural History Society, Oxford and Bombay. 620 pp.

Zhao, Er-mi, and K. Adler. 1993. Herpetology of China. Contributions to Herpetology 10. Society for the Study of Amphibians and Reptiles, Oxford, Ohio. 522 pp.

Other Resources:
Photograph courtesy of Ecologyasia.com

US Fish and Wildlife Service Ecological Risk Screening Summary for Varanus salvator

Author: Somma, L.A.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.