Nile monitor

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Nile monitor
Nile monitor lizard (Varanus niloticus).jpg
Nile monitor lizard (Varanus niloticus) head.jpg
Nile monitor at Lake Baringo, Kenya
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Family: Varanidae
Genus: Varanus
Subgenus: Polydaedalus
V. niloticus
Binomial name
Varanus niloticus
(Linnaeus, 1766)
Nile monitor (varanus niloticus) distribution map.png
Nile monitor's native range (including West Africa Nile monitor, now often recognized as a separate species)
  • Lacerta monitor Linnaeus, 1758nomen rejectum
  • Lacertus tupinambis Lacépède, 1788
  • Lacerta capensis Sparrman, 1783
  • Lacerta nilotica Linnaeus, 1766
  • Tupinambis elegans Daudin, 1802
  • Tupinambus ornatus Daudin, 1803
  • Monitor niloticus Lichtenstein, 1818
  • Monitor pulcher Leach, 1819
  • Stellio saurus Laurenti, 1768
  • Varanus niloticus Mertens, 1942
  • Varanus (Polydaedalus) niloticus ornatus Mertens, 1942
  • Varanus (Polydaedalus) ornatus Böhme & Ziegler, 1997

The Nile monitor (Varanus niloticus) is a large member of the monitor family (Varanidae) found throughout most of Sub-Saharan Africa and along the Nile. The population of West Africa forests and savannahs is sometimes recognized as a separate species, the West African Nile monitor (V. stellatus).[1] Other common names include the African small-grain lizard,[2] water leguaan[3] or river leguaan (leguan, leguaan, and likkewaan mean monitor lizard in South African English, and can be used interchangeably).[4]


Members of the Nile monitor species group were already well known to Africans in ancient times. For example, they were commonly caught, likely as food, in the Djenné-Djenno culture at least a millennium ago.[5]

The Nile monitor twice received a scientific name by Carl Linnaeus: First as Lacerta monitor in 1758 in the 10th edition of Systema Naturae, the starting point of zoological nomenclature. He described it again in 1766 as Lacerta nilotica. Despite being older, the name proposed in 1758 is invalid because it was rejected in ICZN opinion 540, making the name of 1766 valid.[3][6] The genus Varanus was only coined in 1820 by Blasius Merrem. Six years later Leopold Fitzinger moved the Nile monitor into this genus as Varanus niloticus,[7] the currently accepted scientific name for the species.[3]

Species complex[edit]

As traditionally defined, the Nile monitor is a species complex.[1]

The ornate monitor (V. ornatus) and West African Nile monitor (V. stellatus) were described as species in 1802 and 1803 by François Marie Daudin. In 1942, Robert Mertens moved them both into the Nile monitor (V. niloticus); as synonyms or as a valid subspecies.[8] This was the standard treatment until 1997, when a taxonomic review based on color and morphology indicated that the ornate monitor is distinctive and revalidated it as a separate species from rainforests of West and Central Africa.[9] In 2016, a review based primarily on genetics came to another result. They found that monitors from West African forests and adjacent savannah are distinctive and worthy of recognition as a separate species: the West African Nile monitor (V. stellatus).[1] It is estimated to have split from the others in the Nile monitor complex about 7.7 million years ago, making it older than the split between humans and chimpanzees.[5] In contrast, those in the Central African rainforests are genetically similar to the Nile monitor. This essentially splits the ornate monitor—as defined in 1997—into two: the western being the West African Nile monitor and the eastern (of Central African rainforests) being moved back into the Nile monitor. As the type locality for the ornate monitor is in the Central African country of Cameroon, the scientific name V. ornatus becomes a synonym of V. niloticus. Individuals with the "ornate color pattern" and individuals with the "Nile color pattern" occur in both the West African Nile monitor and the Nile monitor, with the "ornate" appearing to be more frequent in densely forested habitats.[1]

With the West African Nile monitor as a separate species, there are two main clades in the Nile monitor: A widespread clade found throughout much of Southern, Central and East Africa, as well as more locally in coastal West Africa. The other clade includes the monitors of the Sahel (Mali to Ethiopia) and Nile regions.[1] Despite the differences, the Reptile Database maintains both the ornate monitor and West African Nile monitor as synonyms of the Nile monitor, but do note that this broad species definition includes distinctive subpopulations.[3]


Nile monitors can grow to about 120 to 220 cm (3 ft 11 in to 7 ft 3 in) in length, with the largest specimens attaining 244 cm (8 ft).[10][11] In an average-sized specimen, the snout-to-vent length will be around 50 cm (1 ft 8 in).[12] In body mass, adults have been reported to vary widely, one study claiming only 0.8 to 1.7 kg (1.8 to 3.7 lb), others state weights ranging from 5.9 to 15 kg (13 to 33 lb) in big monitors. Variations may be due to age or environmental conditions.[13][14][15] Exceptionally large specimens may scale as much as 20 kg (44 lb), but this species weighs somewhat less on average than the bulkier rock monitor.[16] They have muscular bodies, strong legs, and powerful jaws. Their teeth are sharp and pointed in juvenile animals and become blunt and peg-like in adults. They also possess sharp claws used for climbing, digging, defense, or tearing at their prey. Like all monitors, they have forked tongues, with highly developed olfactory properties. The Nile monitor has quite striking, but variable, skin patterns, as they are greyish-brown above with greenish-yellow barring on the tail and large, greenish-yellow rosette-like spots on their backs with a blackish tiny spot in the middle. Their throats and undersides are an ochre-yellow to a creamy-yellow, often with faint barring.[16]

Their nostrils are placed high on their snouts, indicating these animals are highly aquatic. They are also excellent climbers and quick runners on land. Nile monitors feed on fish, snails, frogs, crocodile eggs and young, snakes, birds, small mammals, insects, and carrion. They are also the second largest reptile in the Nile river.

Distribution and habitat[edit]

Nile monitors are native to Sub-Saharan Africa and along the Nile.[17] They are not found in any of the desert regions of Africa (notably Sahara, Kalahari and much of the Horn of Africa), however, as they thrive around rivers.[18][19] Nile monitors were reported to live in and around the Jordan River, Dead Sea, and wadis of the Judaean Desert in Israel until the late 19th Century, though they are now extinct in the region.[20]

Invasive species[edit]

In Florida, United States, established breeding populations of Nile monitors have been known to exist in different parts of the state since at least 1990.[21] Genetic studies have shown that these introduced animals are part of the subpopulation that originates from West Africa and now often is recognized as its own species, the West African Nile monitor.[5] The vast majority of the established breeding population is in Lee County, particularly in the Cape Coral and surrounding regions, including the nearby barrier islands (Sanibel, Captiva, and North Captiva), Pine Island, Fort Myers, and Punta Rassa. Established populations also exist in adjacent Charlotte County, especially on Gasparilla Island.[19] Areas with a sizeable number of Nile monitor sightings in Florida include Palm Beach County just southwest of West Palm Beach along State Road 80.[22] In July 2008, a Nile monitor was spotted in Homestead, a small city southwest of Miami.[23] Other sightings have been reported near Hollywood, Naranja, and as far south as Key Largo in the Florida Keys.[22] 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, Crocodylus acutus) is enormous, given that they normally raid crocodile nests, eat eggs, and prey on small crocodiles in Africa. Anecdotal evidence indicates a high rate of disappearance of domestic pets and feral cats in Cape Coral.[19]

In captivity[edit]

Nile monitors are often found in the pet trade despite a highly aggressive demeanor and resistance to taming. Juvenile monitors will tail whip as a defensive measure, and as adults they are capable of inflicting moderate to serious wounds from biting and scratching. Nile monitors require a large cage as juveniles quickly grow when fed a varied diet, and large adults often require custom-built quarters.



  1. ^ a b c d e Dowell, S.A, D.M. Portik, V. de Buffrenil, I Ineich, E Greenbaum, S.O. Kolokotronis and E.R. Hekkala. 2016. Molecular data from contemporary and historical collections reveal a complex story of cryptic diversification in the Varanus (Polydaedalus) niloticus Species Group. Molecular Phylogenetics and Evolution 94(Part B): 591-604. doi:10.1016/j.ympev.2015.10.004
  2. ^ "Synonyms of Nile Monitor (Veranus niloticus)". Encyclopedia of Life. Retrieved 15 December 2013.
  3. ^ a b c d Varanus niloticus at the Reptile Database. Accessed 15 September 2019.
  4. ^ "leguan - definition". Oxford Dictionaries. Oxford University Press. Retrieved 17 December 2013.
  5. ^ a b c Yong, Ed (20 April 2016). Florida’s Dragon Problem. The Atlantic. Retrieved 15 September 2019.
  6. ^ ICZN (1959). Opinion 540. Protection under the plenary power of the specific names bengalensis Daudin, 1802, as published in the combination Tupinambis bengalensis, and salvator Laurenti 1768, as published in the combination Stellio salvator. Opin. Declar. intern. Com. zool. Nom. 20: 77-85.
  7. ^ Fitzinger, L. (1826). Neue Classification der Reptilien nach ihren natürlichen Verwandtschaften nebst einer Verwandschafts-Tafel und einem Verzeichnisse der Reptilien-Sammlung des K. K. Zoologischen Museums zu Wien. Wien.
  8. ^ Mertens, R. (1942). Die Familie der Warane (Varanidae), 1. Teil: Allgemeines. Abh. Senckenb. naturf. Ges. 462: 1-116.
  9. ^ Böhme, W., and T. Ziegler (1997). A taxonomic review of the Varanus (Polydaedalus) niloticus (Linnaeus, 1766) species complex. The Herpetological Journal 7: 155-162.
  10. ^ Nile Monitor Care Sheet
  12. ^ "Varanus niloticus". Monitor Lizards – Captive Husbandry. Archived from the original on 25 October 2012. Retrieved 15 December 2013.
  14. ^ Hirth & Latif 1979
  18. ^ Reptile Specialists (Nile monitor)
  19. ^ a b c "NAS - Invasive Species FactSheet: Varanus niloticus (Nile monitor)". Nonindenous Aquatic Species. USGS Nonindigenous Aquatic Species Database. Gainesville, FL: United States Geological Survey. Archived from the original on 2009-05-09.
  20. ^ Baker., Tristram, Henry (2013). The Fauna and Flora of Palestine. Cambridge: Cambridge University Press. p. 148. ISBN 9781108042048. OCLC 889948524.
  21. ^ (Campbell, 2003; Enge et al. 2004).
  22. ^ a b Everglades CISMA
  23. ^ Hofmeyer, Erik (10 June 2008). "Homestead ARB home to diverse array of wildlife". Homestead Air Reserve Base News. Homestead Air Reserve Base. Retrieved 15 December 2013.
  24. ^ Bennett, Daniel (1995). A Little Book of Monitor Lizards: A Guide to the Monitor Lizards of the World and Their Care in Captivity. Viper Press. ISBN 978-0952663201.