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The Nile monitor (''Varanus niloticus'') is a large member of the monitor family ( Varanidae) found throughout most of
Sub-Saharan Africa Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
and along the Nile, with invasive populations in
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
. The population in West African forests and savannahs is sometimes recognized as a separate species, the
West African Nile monitor The West African Nile monitor (''Varanus niloticus stellatus'') is a species of monitor lizard that is native to West African forests and adjacent savannah (east to northern Cameroon). It has also been introduced to Florida, United States, whe ...
(''V. stellatus'').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. It is one of the largest lizards in the world reaching and even surpassing the perentie by size. Other common names include the African small-grain lizard, as well as iguana and various forms derived from it, such as guana, water leguaan or river leguaan (leguan, leguaan, and likkewaan mean monitor lizard in
South African English South African English (SAfrE, SAfrEng, SAE, en-ZA) is the set of English language dialects native to South Africans. History British settlers first arrived in the South African region in 1795, when they established a military holding op ...
, and can be used interchangeably). A feral population of the lizards, descended from escaped or intentionally released pets, has become established in several locations in Florida.


Taxonomy

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.Yong, Ed (20 April 2016)
Florida’s Dragon Problem
The Atlantic. Retrieved 15 September 2019.
The Nile monitor twice was given a
scientific name In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...
by Carl Linnaeus: First as ''Lacerta monitor'' in 1758 in the
10th edition of Systema Naturae The 10th edition of ''Systema Naturae'' is a book written by Swedish naturalist Carl Linnaeus and published in two volumes in 1758 and 1759, which marks the starting point of zoological nomenclature. In it, Linnaeus introduced binomial nomencla ...
, 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 ''Rejected'' is an animated film directed by Don Hertzfeldt that was released in 2000. It was nominated for an Academy Award for Best Animated Short Film the following year at the 73rd Academy Awards, and received 27 awards from film festivals ...
in
ICZN The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the I ...
opinion 540, making the name of 1766 valid. The genus '' Varanus'' was coined in 1820 by
Blasius Merrem Blasius Merrem (4 February 1761 – 23 February 1824) was a German naturalist, zoologist, ornithologist, mathematician, and herpetologist. In 1804, he became the professor of political economy and botany at the University of Marburg. Early li ...
. Six years later
Leopold Fitzinger Leopold Joseph Franz Johann Fitzinger (13 April 1802 – 20 September 1884) was an Austrian zoologist. Fitzinger was born in Vienna and studied botany at the University of Vienna under Nikolaus Joseph von Jacquin. He worked at the Vienna Naturhis ...
moved the Nile monitor into this genus as ''Varanus niloticus'', the currently accepted scientific name for the species.


Species complex

As traditionally defined, the Nile monitor is a species complex. The
ornate monitor The ornate monitor (''Varanus niloticus ornatus'') is a monitor lizard that is native to West and Middle Africa. Comprehensive molecular analyses of the group have demonstrated that animals previously assigned to "''Varanus ornatus''" do not con ...
(''V. ornatus'') and
West African Nile monitor The West African Nile monitor (''Varanus niloticus stellatus'') is a species of monitor lizard that is native to West African forests and adjacent savannah (east to northern Cameroon). It has also been introduced to Florida, United States, whe ...
(''V. stellatus'') were described as species in 1802 and 1803 by
François Marie Daudin François Marie Daudin (; 29 August 1776 in Paris – 30 November 1803 in Paris) was a French zoologist. With legs paralyzed by childhood disease, he studied physics and natural history, but ended up being devoted to the latter. Daudin wrote ' ( ...
. In 1942,
Robert Mertens Robert Friedrich Wilhelm Mertens (1 December 1894 – 23 August 1975) was a German herpetologist. Several taxa of reptiles are named after him.Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). ''The Eponym Dictionary of Reptiles''. Baltimore ...
moved them both into the Nile monitor (''V. niloticus''); as
synonyms A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
or as a valid
subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
. This was the standard treatment until 1997, when a
taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
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.Böhme, W., and T. Ziegler (1997). A taxonomic review of the Varanus (Polydaedalus) niloticus (Linnaeus, 1766) species complex. The Herpetological Journal 7: 155-162. 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''). 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
chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
s. 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. With the West African Nile monitor as a separate species, there are two main
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
s in the Nile monitor: A widespread clade found throughout much of
Southern Southern may refer to: Businesses * China Southern Airlines, airline based in Guangzhou, China * Southern Airways, defunct US airline * Southern Air, air cargo transportation company based in Norwalk, Connecticut, US * Southern Airways Express, M ...
, Central and
East Africa East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territories make up Eastern Africa: Due to the historical ...
, as well as more locally in coastal West Africa. The other clade includes the monitors of the
Sahel The Sahel (; ar, ساحل ' , "coast, shore") is a region in North Africa. It is defined as the ecoclimatic and biogeographic realm of transition between the Sahara to the north and the Sudanian savanna to the south. Having a hot semi-arid c ...
( Mali to Ethiopia) and Nile regions. 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.


Description

The Nile monitor is Africa's longest lizard. They grow from about in length, with the largest specimens attaining . In an average-sized specimen, the snout-to-vent length will be around . In body mass, adults have been reported to vary widely, one study claiming only , others state weights ranging from in big monitors. Variations may be due to age or environmental conditions. Exceptionally large specimens may scale as much as , but this species weighs somewhat less on average than the bulkier
rock monitor The rock monitor (''Varanus albigularis'') is a species of monitor lizard in the family Varanidae. The species is endemic to Central, East, and southern Africa. It is the second-longest lizard found on the continent, and the heaviest-bodied; lo ...
. 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 The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...
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. Their nostrils are placed high on their snouts, indicating these animals are very well adapted for an aquatic lifestyle. They are also excellent climbers and quick runners on land. Nile monitors feed on a wide variety of prey items, including fish, frogs, toads (even poisonous ones of the genera ''
Breviceps ''Breviceps'' is a genus of frogs in the family Brevicipitidae. Species in the genus ''Breviceps'' are commonly known as rain frogs or short-headed frogs. They occur in arid to semiarid climates of East Africa and Southern Africa. Taxonomy The ...
'' and ''
Sclerophrys ''Sclerophrys'' is a genus of "true toads", family Bufonidae, native to Africa and the southern Arabian Peninsula. Originally, all of these species were classified in the genus ''Bufo''. The genus, originally named ''Amietophrynus'', was split du ...
''), small reptiles (such as turtles, snakes,
lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
s, and young
crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...
s), birds, rodents, other small mammals (up to
domestic cats The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of t ...
and young antelopes 'Raphicerus''">Raphicerus.html" ;"title="'Raphicerus">'Raphicerus'', eggs (including those of crocodiles, agamids, other monitor lizards, and birds), invertebrates (such as beetles, termites, orthopterans, crabs, caterpillars, spiders, millipedes, earthworms, snails, and slugs), carrion, human wastes, and feces.


Distribution and habitat

Nile monitors are native to
Sub-Saharan Africa Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
and along the Nile. They are not found in any of the
desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
regions of Africa (notably
Sahara , photo = Sahara real color.jpg , photo_caption = The Sahara taken by Apollo 17 astronauts, 1972 , map = , map_image = , location = , country = , country1 = , ...
, Kalahari and much of the
Horn of Africa The Horn of Africa (HoA), also known as the Somali Peninsula, is a large peninsula and geopolitical region in East Africa.Robert Stock, ''Africa South of the Sahara, Second Edition: A Geographical Interpretation'', (The Guilford Press; 2004), ...
), however, as they thrive around rivers. Nile monitors were reported to live in and around the
Jordan River The Jordan River or River Jordan ( ar, نَهْر الْأُرْدُنّ, ''Nahr al-ʾUrdunn'', he, נְהַר הַיַּרְדֵּן, ''Nəhar hayYardēn''; syc, ܢܗܪܐ ܕܝܘܪܕܢܢ ''Nahrāʾ Yurdnan''), also known as ''Nahr Al-Shariea ...
,
Dead Sea The Dead Sea ( he, יַם הַמֶּלַח, ''Yam hamMelaḥ''; ar, اَلْبَحْرُ الْمَيْتُ, ''Āl-Baḥrū l-Maytū''), also known by other names, is a salt lake bordered by Jordan to the east and Israel and the West Bank ...
, and wadis of the Judaean Desert in Israel until the late 19th century, though they are now extinct in the region.


Invasive species

In Florida in the United States, established breeding populations of Nile monitors have been known to exist in different parts of the state since at least 1990.(Campbell, 2003; Enge et al. 2004). 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 The West African Nile monitor (''Varanus niloticus stellatus'') is a species of monitor lizard that is native to West African forests and adjacent savannah (east to northern Cameroon). It has also been introduced to Florida, United States, whe ...
. 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 Sanibel is an island and city in Lee County, Florida, United States. The population was 6,382 at the 2020 United States census, 2020 census. It is part of the Cape Coral-Fort Myers, Florida Metropolitan Statistical Area. The island, also known as ...
, Captiva, and
North Captiva North Captiva Island is an island in Lee County in Southwest Florida, located just offshore in the Gulf of Mexico. It lies just north of Captiva Island, separated by a channel called Redfish Pass which was created in a 1921 hurricane. It li ...
), Pine Island, Fort Myers, and
Punta Rassa Punta Rassa is an unincorporated community and census-designated place (CDP) in Lee County, Florida, United States. The population was 1,620 at the 2020 census. It is part of the Cape Coral-Fort Myers, Florida Metropolitan Statistical Area. Geog ...
. Established populations also exist in adjacent Charlotte County, especially on Gasparilla Island. Other areas in Florida with a sizeable number of Nile monitor sightings include Palm Beach County just southwest of West Palm Beach along State Road 80. In July 2008, a Nile monitor was spotted in Homestead, a small city southwest of Miami. Other sightings have been reported near
Hollywood Hollywood usually refers to: * Hollywood, Los Angeles, a neighborhood in California * Hollywood, a metonym for the cinema of the United States Hollywood may also refer to: Places United States * Hollywood District (disambiguation) * Hollywood, ...
, Naranja, and as far south as Key Largo in the Florida Keys. The potential for the established population of Nile monitors in Lee, Charlotte, and other counties in Florida, to negatively impact indigenous crocodilians, such as American alligators (''Alligator mississippiensis''), and American crocodiles (''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.


In captivity

Nile monitors are often found in the pet trade despite their 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.
''"There are few lizards less suited to life in captivity than the Nile monitor. Buffrenil (1992) considered that, when fighting for its life, a Nile monitor was a more dangerous adversary than a crocodile of a similar size. Their care presents particular problems on account of the lizards' enormous size and lively dispositions. Very few of the people who buy brightly-coloured baby Nile monitors can be aware that, within a couple of years, their purchase will have turned into an enormous, ferocious carnivore, quite capable of breaking the family cat's neck with a single snap and swallowing it whole."''


References

{{Taxonbar, from=Q737896 Varanus Lizards of Africa Reptiles of West Africa Reptiles described in 1766 Taxa named by Carl Linnaeus Reptiles of South Africa Reptiles as pets