| Nile monitor | |
|---|---|
_2.jpg) | |
| Botswana | |
_head.jpg) | |
| Lake Baringo, Kenya | |
CITES Appendix II | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Suborder: | Anguimorpha |
| Family: | Varanidae |
| Genus: | Varanus |
| Subgenus: | Polydaedalus |
| Species: | V. niloticus |
| Binomial name | |
| Varanus niloticus (Linnaeus, 1766) | |
_distribution_map.png) | |
| Nile monitor's native range (includingWest Africa Nile monitor, now often recognized as a separate species) | |
| Synonyms | |
List
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TheNile monitor (Varanus niloticus) is a large member of themonitor family (Varanidae) found throughout most ofSub-Saharan Africa, particularly in drier regions, and along theNile River and its tributaries inEast Africa. Additionally, there are modern, invasive populations inNorth America. The population found inWest African forests and savannahs is sometimes recognized as a separate species, theWest African Nile monitor (V. stellatus).[3] While it is dwarfed by its larger relatives, such as theKomodo dragon, theAsian water monitor or thecrocodile monitor, it is stillone of the largest lizards in the world, reaching (and even surpassing) Australia'sperentie in size. Other common names include theAfrican small-grain lizard,[4] as well asiguana and various forms derived from it,[5] such asguana,water leguaan[6] orriver leguaan (leguan, leguaan, and likkewaan mean monitor lizard inSouth African English, and can be used interchangeably).[7]
A feral population of Nile monitors (descended from escaped or intentionally-released pets) has become established in several locations inSouth Florida.[8] In addition to any illegally-released animals, it is speculated that during particularly intensehurricane seasons in Florida, many reptiles potentially escape when their enclosures are damaged or inadvertently unlocked; as Florida has a semi-tropical to tropical climate, many reptiles are housed outdoors, and poorly-secured enclosures may become damaged during bad storms. Along with Nile monitors, Florida is infamous for its feral populations ofagamas,Argentine black and white tegus,Burmese pythons,green iguanas,Madagascar giant day geckos, andpanther andveiled chameleons, among others. Many of these species are thought to be descendants of hurricane escapees.
Members of the Nile monitorspecies group were already well known to Africans in ancient times. For example, they were commonly caught, likely as food, in theDjenné-Djenno culture at least a millennium ago.[9]
The Nile monitor twice was given ascientific name byCarl Linnaeus: First asLacerta monitor in 1758 in the10th edition of Systema Naturae, the starting point ofzoological nomenclature. He described it again in 1766 asLacerta nilotica. Despite being older, the name proposed in 1758 is invalid because it wasrejected inICZN opinion 540, making the name of 1766 valid.[6][10] The genusVaranus was coined in 1820 byBlasius Merrem. Six years laterLeopold Fitzinger moved the Nile monitor into this genus asVaranus niloticus,[11] the currently accepted scientific name for the species.[6]
As traditionally defined, the Nile monitor is aspecies complex.[3]Theornate monitor (V. ornatus) andWest African Nile monitor (V. stellatus) were described as species in 1802 and 1803 byFrançois Marie Daudin. In 1942,Robert Mertens moved them both into the Nile monitor (V. niloticus); assynonyms or as a validsubspecies.[12] This was the standard treatment until 1997, when ataxonomic review based on color andmorphology indicated that the ornate monitor is distinctive and revalidated it as a separate species from rainforests ofWest andCentral Africa.[13] In 2016, a review based primarily ongenetics came to another result. They found that monitors fromWest African forests andadjacent savannah are distinctive and worthy of recognition as a separate species: the West African Nile monitor (V. stellatus).[3] 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 andchimpanzees.[9] 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 thetype locality for the ornate monitor is in the Central African country ofCameroon, the scientific nameV. ornatus becomes a synonym ofV. 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.[3]
With the West African Nile monitor as a separate species, there are two mainclades in the Nile monitor: A widespread clade found throughout much ofSouthern, Central andEast Africa, as well as more locally in coastal West Africa. The other clade includes the monitors of theSahel (Mali toEthiopia) andNile regions.[3] Despite the differences, theReptile 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.[6]
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The Nile monitor is Africa's longest lizard.[14] They grow from 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).[15][16] In an average-sized specimen, the snout-to-vent length will be around 50 cm (1 ft 8 in).[17] 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.[18][19][20] Exceptionally large specimens may scale as much as 20 kg (44 lb), but this species weighs somewhat less on average than the bulkierrock monitor.[21]
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 sharpclaws used for climbing, digging, defense, or tearing at their prey. Like all monitors, they have forked tongues, with highly developedolfactory 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-yellowrosette-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.[21]
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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 and toads (even poisonous ones of the generaBreviceps andSclerophrys), small reptiles (such asturtles,snakes,lizards, and youngcrocodiles), birds, rodents, other small mammals (up todomestic cats and young antelopes [Raphicerus]), eggs (including those of crocodiles, agamids, other monitor lizards, and birds), invertebrates (such asbeetles,termites,orthopterans,crabs,caterpillars,spiders,millipedes,earthworms,snails, andslugs),carrion, human wastes, and feces.[22][23][24][25][26]
Nile monitors are native toSub-Saharan Africa and along theNile.[27] They are not found in any of thedesert regions of Africa (notablySahara,Kalahari and much of theHorn of Africa), however, they thrive around rivers.[28][29] Nile monitors were reported to live in and around theJordan River,Dead Sea, andwadis of theJudaean Desert inIsrael until the late 19th century, though they are now extinct in the region.[30]
InFlorida 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.[31] 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, theWest African Nile monitor.[9] The vast majority of the established breeding population is inLee County, particularly in theCape Coral and surrounding regions, including the nearby barrier islands (Sanibel,Captiva, andNorth Captiva),Pine Island,Fort Myers, andPunta Rassa. Established populations also exist in adjacentCharlotte County, especially onGasparilla Island.[29] Other areas in Florida with a sizeable number of Nile monitor sightings includePalm Beach County just southwest of West Palm Beach alongState Road 80.[32] In July 2008, a Nile monitor was spotted inHomestead, a small city southwest ofMiami.[33] Other sightings have been reported nearHollywood,Naranja, and as far south asKey Largo in the Florida Keys.[32] The potential for the established population of Nile monitors in Lee, Charlotte, and other counties in Florida, to negatively impact indigenous crocodilians, such asAmerican alligators (Alligator mississippiensis), andAmerican crocodiles (Crocodylus acutus), is enormous, given that they normally raid crocodile nests, eat eggs, andprey on small crocodiles in Africa. Anecdotal evidence indicates a high rate of disappearance of domestic pets and feral cats in Cape Coral.
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.[34]
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