Disclaimer:

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: Nile Monitor

Taxonomy: available through www.itis.gov

Identification: A large lizard with a snout-vent length averaging 0.6-0.8 m (23.6-31.5 in), and a total length that may exceed 2.42 m (over 7.5 ft) and weigh over 10 kg (about 22 lbs) (Bennett, 1998; Branch, 1998; Spawls et al., 2002; Lenz, 2004). Dorsally the color is gray-brown or dark olive with darker reticulation, and 6-9 bands or bands of yellow-gold ocelli in adults; juveniles are a more brightly patterned black and yellow (De Lisle, 1996; Branch, 1998; Spawls et al., 2002; Lenz, 2004). The tongue is blue (Bennett, 1998; Campbell, 2003). These lizards have large, strong claws, a neck longer than the narrow-snouted head, and a laterally compressed tail (Steel, 1996; Lamar, 1997; Branch, 1998; Lenz, 2004). No other lizard indigenous to the U.S. reaches this large size and exhibits these anatomical features. Illustrations of Varanus niloticus are in Cowles (1930, 1959), Patterson and Bannister (1987), Sprackland (1992), Branch, (1993, 1998), De Lisle (1996), Steel (1996), Lamar (1997), Rogner (1997), Bennett (1998), Spawls et al. (2002), Campbell (2003), Enge et al. (2004), Lenz (2004), and Pianka et al. (2004).

Size: 0.6 – 0.8 m SVL; may exceed 2.42 m TL and weigh over 10 kg.

Native Range: Throughout southern and most of the central African continent, including Sudan and a small portion of south-central Egypt, but excluding Madagascar (Cowles, 1930; Cansdale, 1955; Patterson and Bannister, 1987; Branch, 1993, 1998; De Lisle, 1996; Schleich et al., 1996; Steel, 1996; Rogner, 1997; Bennett, 1998; Spawls et al., 2002; Lenz, 2004). 

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

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

Means of Introduction: Probable pet escapees and intentional releases (Enge et al., 2004).

Status: Not established in Hillsborough and Monroe Counties, Florida.  Established in at least a 50 km2 area of Cape Coral (including nearby barrier islands, and Punta Rassa, Lee County, Florida (Campbell, 2003; Enge et al., 2004; Krysko in Goodnough, 2004; McGrath, 2005; ; McGrady in Anonymous, 2007; K. Krysko, personal communication 2003), and invasively spreading to adjacent Charlotte County and perhaps other counties in Florida, through the coastal mangrove swamps and canals (Enge et al., 2004). Nile monitors are established in Charlotte County (especially Gasparilla Island), and Cay Costa, Pine Island and probably Sanibel Island, Lee County. Individual V. niloticus are occasionally seen in other parts of Florida, but it is unclear if these and others sighted or collected in Alachua, Broward, Collier, De Soto, Miami-Dade, Orange, and Palm Beach Counties are single pet escapees or part of one or more established populations (Enge et al., 2004; Anonymous, 2007).

Impact of Introduction:

Summary of species impacts derived from literature review. Click on an icon to find out more...

Ecological	Economic	Human Health

None in Hillsborough and Monroe Counties, Florida. The impact of V. niloticus in Alachua, Broward, Collier, Charlotte County, De Soto, Orange, Palm Beach, and Miami-Dade Counties, Florida, is unknown. The potential for the established population of Nile monitors in Lee, Charlotte, and other counties in Florida, to negatively impact indigenous crocodilians (American alligator, Alligator mississippiensis, and American crocodile, C. acutus) is enormous given their preference for raiding nests and eating eggs and young of and exhibiting dietary competition with crocodiles in Africa (Roosevelt, 1910; Cansdale, 1955; Cott, 1961; Patterson and Bannister, 1987; Branch, 1993, 1998; Lenz, 1995, 2004; De Lisle, 1996; Bennett, 1998; Luiselli et al., 1999; Campbell, 2003; Enge et al., 2004). Additionally, V. niloticus eats the eggs of birds and domesticated poultry (Cowles, 1930, 1959; Patterson and Bannister, 1987; De Lisle, 1996; Bennett, 1998; Lenz, 2004), which give them great potential to negatively impact both native birds and domestic poultry operations in Florida (Enge et al., 2004). Of particular concern are burrowing owls (Athene cunicularia) and gopher tortoises (Gopherus polyphemus); two legally protected species inhabiting the Cape Coral area of Florida (Campbell, 2003; Enge et al., 2004). Anecdotal evidence indicates a high rate of disappearance of domestic pets and feral cats in Cape Coral (Campbell, 2003).  Moreover, exotic parasites harbored by Nile monitors could potentially impact indigenous vertebrates and humans (Burridge and Simmons, 2003; Campbell, 2003; Lenz, 2004).

Nile monitors have made no impact upon California (Lemm, 2006).

Varanus niloticus can defend themselves with their teeth, sharp claws, or by using the tail as a whip (Cowles, 1930; Bennett, 1998; Lenz, 2004). Their size and defensive disposition makes them potentially dangerous to humans and their domestic pets.  In a bizarre, well-publicized incident, the corpse of a deceased pet owner in Newark, Delaware, was found as the owner’s seven pet Nile monitors were devouring it; the cause of the pet owner’s death was not known ([Chase], 2002). According to Krysko (in Goodnough, 2004), “…no one realizes the ability this animal has to tear off your cat’s head with one twist.” Of all the species of Varanus available to hobbyists, V. niloticus is the least suitable species to keep in captivity (Bennett, 1998; Enge et al., 2004).

Thorough ecological studies on the established population of Nile monitors in Lee and Charlotte Counties in addition to an investigation concerning the feasibility of an eradication program are underway to fully determine the impact of this large carnivorous lizard in Florida (Campbell, 2003; Enge et al., 2004). Current evidence suggests that total eradication of this species from Florida is no longer feasible (Campbell, 2003; Enge et al., 2004). Moreover, efforts are being made to determine if V. niloticus has actually spread to other Florida counties (Campbell, 2003; Enge et al., 2004). Given the existence of at least one established population, the presence of seemingly stray individuals in other parts of Florida should not be dismissed as single pet escapees or releases without further study.
 

Remarks: The natural history of the Nile monitor has been summarized by a variety of authors (Cowles, 1928, 1930, 1959; Cansdale, 1955; Patterson and Bannister, 1987; Branch, 1993, 1998; de Buffrénil et al., 1994; Lenz, 1995, 2004; De Lisle, 1996; Rogner, 1997; Bennett, 1998; Luiselli et al., 1999; de Buffrénil and Hémery, 2002; Campbell, 2003; Enge et al., 2004; Pianka, 2004; Switak, 2004; Baha El Din, 2006).  The most complete taxonomic summaries are by Ast (2001) and Jennings and Pianka (2004), and literature reviews are by Lenz (1995, 2004) and Bennett (1998).

These intelligent, adaptable lizards are not habitat-specific and can be found in almost any habitat where permanent bodies of water exist (Lenz, 1995, 2004; Bennett, 1998; Luiselli et al., 1999). African populations live under a wide variety of climatic conditions including temperate regions of South Africa where they can hibernate during cold weather (Bennett, 1998; Branch, 1998; Lenz, 2004). In parts of Kenya, densities of Nile monitors are 40-60 lizards/km2 (Western, 1974). In Lee County, Florida, V. niloticus inhabits estuarine and exotic plant communities, pine flatwoods, barrier islands, man-made canals (including a 644 km long network), suburban developments, golf courses and associated ponds, and areas close to urban development (Campbell, 2003; Enge et al., 2004; Anonymous, 2007). Home burrows are commonly found along canal banks in Lee County (Campbell, 2003; Enge et al., 2004). These semiaquatic lizards are omnicarnivorous; eating invertebrates (especially crabs), carrion, human feces, young crocodiles, conspecifics, eggs of birds, turtles and crocodiles, and any terrestrial or aquatic vertebrate which it can overpower and consume (Roosevelt, 1910; Cowles, 1930; Cansdale, 1955; Cott, 1961; Patterson and Bannister, 1987; Losos and Greene, 1988; Branch, 1993, 1998; Lenz, 1995, 2004; De Lisle, 1996; Steel, 1996; Lamar, 1997; Bennett, 1998; Luiselli et al., 1999; Bayless and Pierson, 2003; Campbell, 2003).  Nile monitors can forage in trees, on or below ground, and in water (Lenz, 1995, 2004; Bennett, 1998; Campbell, 2003). The highly fecund females lay eggs and bury them in the ground or in active termitaria (termite mounds) (Roosevelt, 1910; Cowles, 1928, 1930, 1959; Patterson and Bannister, 1987; Bennett, 1998; Branch, 1998). Most authors state that the young hatch out without assistance (Cowles, 1928, 1930, 1959; Patterson and Bannister, 1987; Branch, 1988; Bennett, 1998; Spawls et al., 2002; Lenz, 2004), but Bauer (1998) suggests that females return to termitaria to dig their hatchlings out of the nest; a behavior that may be more common in varanids (monitors) than previously known (Somma, 2003a, b). Initial growth rates of juvenile V. niloticus are rapid and individuals may live more than 10-15 years (de Buffrénil et al., 1994; De Lisle, 1996; de Buffrénil and Hémery, 2002; Campbell, 2003; Lenz, 2004).

Varanus niloticus is a lizard that is much exploited for its meat and skin (Cowles, 1930; Cansdale, 1955; de Buffrénil et al., 1994; Bennett, 1998; de Buffrénil and Hémery, 2002; Spawls et al., 2002; Baha El Din, 2006), and to a lesser extent the pet trade (Sprackland, 1992; Rogner, 1997; Baha El Din, 2006). Nile monitors are protected under C.I.T.E.S., Appendix II (Levell, 1997; Branch, 1998); mandatory regulation of international trade is through permits (Levell, 1997). It is illegal to intentionally release any nonindigenous reptile or other animal in the state of Florida (Townsend et al., 2003).

The establishment of V. niloticus in at least two counties in Florida makes it the largest, most dangerous nonindigenous lizard in the United States. Nile monitors, or at least those originating from populations in temperate Africa, are adapted to temperate climates. If such an adaptation is population-specific, efforts should be made to use DNA analysis to determine the geographic origin of the V. niloticus established in Florida. Nile monitors that are temperate-adapted will eventually spread throughout Florida and the Gulf States, and further north along the Atlantic Coast at least as far north as Georgia and, perhaps, the Carolinas. Their presence in the United States presents a cause for serious concern.
 

 

References: (click for full references)

Anonymous. [2002]. Monitor lizards [online]. Available on URL: http://www.animalcapture.com/pages/monitor_lizards.htm. In: Animal Capture of Florida.

Anonymous. 2007. Nile monitor [online]. Available on URL: http://myfwc.com/critters/exotics/SpeciesNumberResults.asp?SPPNO=291. In: Florida’s Exotic Wildlife. Florida Fish and Wildlife Conservation Commission, Tallahassee.

Ast, J. C. 2001. Mitochondrial DNA evidence and evolution in Varanoidea (Squamata). Cladistics 17(3):211-226.

Baha El Din, S. 2006. A Guide to the Reptiles and Amphibians of Egypt. The American University in Cairo Press, Cairo – New York. 359 pp.

Bauer, A. M. 1998. Lizards. Pp. 128-173. In: H. G. Cogger and R. G. Zweifel (editors). Encyclopedia of Amphibians & Reptiles. Second Edition. Academic Press, San Diego. 240 pp.

Bayless, M. K., and B. Pierson. 2003. Varanus niloticus (Nile monitor): Captive adult feeding on ants. Herpetological Bulletin (85):29-30.

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

Branch, B. [=W. R.] 1993. Southern African Snakes and Other Reptiles. A Photographic Guide. New Holland (Publishers) Ltd, London. 144 pp.

Branch, B. [=W. R.] 1998. Field Guide to Snakes and Other Reptiles of Southern Africa. Third Revised Edition. Ralph Curtis Books Publishing, Sanibel Island, Florida. 399 pp.

Burridge, M. J., and L. A. Simmons. 2003. Exotic ticks introduced into the United States on imported reptiles from 1962 to 2001 and their potential roles in international dissemination of diseases. Veterinary Parasitology 113:289-320.

Campbell, T. [S.] 2003. Species profile: Nile monitors (Varanus niloticus) in Florida. Iguana 10(4):119-120.

Cansdale, G. 1955. Reptiles of West Africa. Penguin Books Ltd, Harmondsworth, England. 104 pp.

[Chase, R.] 2002. Pet lizards eat dead owners flesh. Associated Press on Kingsnake.com [online] (21 January), Available on URL: http://forum.kingsnake.com/njhs/messages/214.html.

Cott, H. B. 1961. Scientific results of an inquiry into the ecology and economic status of the Nile crocodile (Crocodilus niloticus) in Uganda and Northern Rhodesia. Transactions of the Zoological Society of London 29(4):211-356, plates 1-9.

Cowles, R. B. 1928. The life history of Varanus niloticus. Science 67(1734):317-318.

Cowles, R. B. 1930. The life history of Varanus niloticus (Linnaeus) as observed in Natal South Africa. Journal of Entomology and Zoology 22(1):1-31, plates I-VII.

Cowles, R. B. 1959. Zulu Journal. Field Notes of A Naturalist in South Africa. University of California Press, Berkeley and Los Angeles. 267 pp.

de Buffrénil, V., C. Chabanet, and J. Castanet. 1994. Données préliminaries sur la taille, la croissance et la longevévité du varan du Nil (Varanus niloticus) dans la région du lac Tchad. Canadian Journal of Zoology 72(2):262-273.

de Buffrénil, V., and G. Hémery. 2002. Variation in longevity, growth, and morphology in exploited Nile monitors (Varanus niloticus) from Sahelian Africa. Journal of Herpetology 36(3):419-426.

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

Duquesnel, J. 1996. Scaly Visitors. Resource Management Notes (Florida Department of Environmental Protection, Tallahassee) 8(2):40.

Enge, K. M., K. L. Krysko, K. R. Hankins, T. S. Campbell, and F. W. King. 2004. Status of the Nile monitor (Varanus niloticus) in southwestern Florida. Southeastern Naturalist 3(4):571-582.

Goodnough, A. 2004. Exotic pets on the loose throughout South Florida. The Gainesville Sun 128(239; 29 Feb.):8B.

Jennings, W. B., and E. R. Pianka. 2004. Tempo and timing of the Australian Varanus radiation. Pp. 77-87. In: E. R. Pianka, D. R. King and R. A. King (editors), Varanoid Lizards of the World. Indiana University Press, Bloomington and Indianapolis. 588 pp.

Krysko, K. L. 2003. Personal communication—Collection Manager, Division of Herpetology, Florida Museum of Natural History, University of Florida, Gainesville, Florida, 32611-7800.

Lamar, W. W. 1997. The World's Most Spectacular Reptiles & Amphibians. World Publications, Tampa. 208 pp.

Lenz, S. 1995. Zur Biologie und Ökologie des Nilwarans, Varanus niloticus, in Gambia, Westafrika. Mertensiella (Rheinbach) 5:1-256.

Lenz, S. 2004. Varanus niloticus. Pp. 133-138. In: E. R. Pianka, D. R. King and R. A. King (eds), Varanoid Lizards of the World. Indiana University Press, Bloomington and Indianapolis. 588 pp.

Levell, 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.

Losos, J. B., and H. W. Greene. 1988. Ecological and evolutionary implications of diet in monitor lizards. Biological Journal of the Linnean Society 35(4):379-407.

Luiselli, L., G. C. Akani, and D. Capizzi. 1999. Is there any interspecific competition between dwarf crocodiles (Osteolaemus tetraspis) and Nile monitors (Varanus niloticus) in the swamps of central Africa? A study from southeastern Nigeria. Journal of Zoology, London 247(1):127-131.

McGrath, S. 2005. Attack of the alien invaders. National Geographic 207(3):92-117.

Patterson, R., and A. Bannister. 1987. Reptiles of Southern Africa. C. Struik Publishers, Cape Town. 128 pp.

Pianka, E. R. 2004. Evolution of body size and reproductive tactics. Pp. 549-555. In: E. R. Pianka, D. R. King and R. A. King (editors), Varanoid Lizards of the World. Indiana University Press, Bloomington and Indianapolis. 588 pp.

Pianka, E. R., D. R. King, and R. A. King (editors). 2004. Varanoid Lizards of the World. Indiana University Press, Bloomington and Indianapolis. 588 pp.

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

Roosevelt, T. 1910. African Game Trails. An Account of the African Wanderings of An American Hunter-Naturalist. Charles Scribner's Sons, New York. 583 pp.

Schleich, H. H., W. Kästle, and K. Kabish. 1996. Amphibians and Reptiles of North Africa. Koeltz Scientific Publishers, Koenigstein. 630 pp.

Somma, L. A. 2003a. Parental Behavior in Lepidosaurian and Testudinian Reptiles. A Literature Survey. Krieger Publishing Company, Malabar, Florida. 174 pp.

Somma, L. A. 2003b. Reptilian parental behaviour. The Linnean (London) 19(3):42-46.

Spawls, S., K. Howell, R. Drewes, and J. Ashe. 2002. A Field Guide to the Reptiles of East Africa. Academic Press, San Diego. 543 pp.

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

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

Switak, K.-H. 2004. Field notes for Varanus niloticus/ornatus in Sub-Saharan Africa. Bulletin of the Chicago Herpetological Society 39(3):41-44.

Townsend, J. H., K. L. Krysko, and K. M. Enge. 2003. Introduced iguanas in southern Florida: A history of more than 35 years. Iguana 10(4):111-118.

Western, D. 1974. The distribution, density and biomass density of lizards in a semi-arid environment of northern Kenya. East African Wildlife Journal 12(1):49-62.

 

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.