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| NAS - Nonindigenous Aquatic Species |
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Common Name: Nile Monitor
Taxonomy: available through 
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
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).
Nonindigenous Occurrences: A V. niloticus was trapped in Brandon, Hillsborough County, Florida (Anonymous, [2002]). Another individual was captured at Key Largo, Monroe County, Florida, near nesting sites of Crocodylus acutus, the American crocodile (Duquesnel, 1996). A population of Nile monitors has been observed in the Cape Coral area, Lee County, Florida, since 1990 (Campbell, 2003; Enge et al., 2004; Repenning in Anonymous, 2007). A V. niloticus was observed escaping into a burrow on Gasparilla Island, Charlotte County, adjacent to Lee County (Repenning in Enge et al., 2004, and in Anonymous, 2007). Additional sightings in Lee County, Florida, are from Cayo Costa, Pine Island, Sanibel Island, and south of the Caloosahatchee River in Punta Rassa and Fort Myers (K. Krysko, personal communication 2003; Enge et al., 2004). Nile monitors have been regularly observed in the Coral Springs-Tamarac area, Broward County, Florida for 10 years (Lucas in Enge et al., 2004), and on 29 May 2007 a specimen was collected from Broward County (Florida Museum of Natural History, Herpetology Collection, UF 151233). A variety of sightings exist for Fort Ogden, Arcadia, and Brownville in De Soto County (Clark in Enge et al., 2004) and Haldeman Creek, west of Bayshore Drive, Naples, Collier County, Florida (Seitz in Enge et al., 2004). A voucher photograph (Florida Museum of Natural History, Herpetology Collection, UF 138065) exists for a V. niloticus in Lake Price, Orange County, Florida (Enge et al., 2004) and one or more individual Varanus, probably V. niloticus, was sighted in the Lost Lake subdivision of Casselberry, Orange County, in May 2007, culminating in one being shot by a police officer on 28 May 2007, but still escaping (Langbeinand and Pedicini, 2007). Additionally, the Florida Museum of Natural History, Herpetology Collection, has a specimen from Palm Beach County, Florida, collected on 9 May 2007 (UF 151185). Other Florida V. niloticus sightings occur regularly at Matheson Hammock (Enge et al., 2004; Krysko in Anonymous, 2007) and Card Sound Road (Moler, Roudebush and Crutchfield in Enge et al., 2004; Moler in Anonymous, 2007), Miami-Dade County, Florida. In northern Florida one individual was collected in Lake Kanapaha, Alachua County, in 1981 (Enge in Anonymous, 2007). At least one V. niloticus was collected in San Diego County, California (Lemm, 2006).
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:
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
Anonymous. [2002]. Monitor lizards [online]. Available on URL: http://www.animalcapture.com/pages/monitor_lizards.htm. In: Animal Capture of
Anonymous. 2007.
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
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,
Bayless, M. K., and B. Pierson. 2003. Varanus niloticus (
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
Branch, B. [=W. R.] 1998. Field Guide to Snakes and Other Reptiles of
Burridge, M. J., and L. A. Simmons. 2003. Exotic ticks introduced into the
Campbell, T. [S.] 2003. Species profile: Nile monitors (Varanus niloticus) in
Cansdale, G. 1955. Reptiles of
[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
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
Cowles, R. B. 1959. Zulu Journal. Field Notes of A Naturalist in
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
De Lisle, H. F. 1996. The Natural History of Monitor Lizards. Krieger Publishing Company,
Duquesnel, J. 1996. Scaly Visitors. Resource Management Notes (Florida Department of Environmental Protection,
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
Goodnough, A. 2004. Exotic pets on the loose throughout
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,
Lenz, S. 1995. Zur Biologie und Ökologie des Nilwarans, Varanus niloticus, in
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.
Levell, J. P. 1997. A Field Guide to Reptiles and the Law. Second Revised Edition. Serpent's Tale Natural History Book Distributors,
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
McGrath, S. 2005. Attack of the alien invaders. National Geographic 207(3):92-117.
Patterson, R., and A. Bannister. 1987. Reptiles of
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.
Pianka, E. R., D. R. King, and R. A. King (editors). 2004. Varanoid Lizards of the World.
Rogner, M. 1997. Lizards. Vol. 2. English Edition. Krieger Publishing Company,
Roosevelt, T. 1910. African Game Trails. An Account of the African Wanderings of An American Hunter-Naturalist. Charles Scribner's Sons,
Schleich, H. H., W. Kästle, and K. Kabish. 1996. Amphibians and Reptiles of
Somma, L. A. 2003a. Parental Behavior in Lepidosaurian and Testudinian Reptiles. A Literature Survey. Krieger Publishing Company,
Somma, L. A. 2003b. Reptilian parental behaviour. The Linnean (
Spawls, S., K. Howell, R. Drewes, and J. Ashe. 2002. A Field Guide to the Reptiles of
Sprackland, R. G. 1992. Giant Lizards. T.F.H. Publications, Inc.,
Steel, R. 1996. Living Dragons. A Natural History of the World's Monitor Lizards. Blandford,
Switak, K.-H. 2004. Field notes for Varanus niloticus/ornatus in Sub-Saharan Africa. Bulletin of the
Townsend, J. H., K. L. Krysko, and K. M. Enge. 2003. Introduced iguanas in southern
Western, D. 1974. The distribution, density and biomass density of lizards in a semi-arid environment of northern
Author: Louis A. Somma
Revision Date: 8/28/2007 Citation for this information:
Louis A. Somma. 2009. Varanus niloticus. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1085> Revision Date: 8/28/2007
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