The Nile monitor (Varanus niloticus) is a large member of the monitor family (Varanidae) found throughout most of Sub-Saharan Africa, particularly in drier regions, and along the Nile River and its tributaries in East Africa. Additionally, there are modern, invasive populations in North America. The population found in West African forests and savannahs is sometimes recognized as a separate species, the West African Nile monitor (V. niloticus stellatus) and Ornate monitor (V. niloticus ornatus). While it is dwarfed by its larger relatives, such as the Komodo dragon, the Asian water monitor or the crocodile monitor, it is still one of the largest lizards in the world, reaching (and even surpassing) Australia's perentie in 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, and can be used interchangeably).

A feral population of Nile monitors (descended from escaped or intentionally-released pets) has become established in several locations in South Florida. In addition to any illegally-released animals, it is speculated that during particularly intense hurricane 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 of agamas, Argentine black and white tegus, Burmese pythons, green iguanas, Madagascar giant day geckos, and panther and veiled chameleons, among others. Many of these species are thought to be descendants of hurricane escapees.

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.

The Nile monitor twice was given 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. The genus Varanus was coined in 1820 by Blasius Merrem. Six years later Leopold Fitzinger moved the Nile monitor into this genus as Varanus niloticus, the currently accepted scientific name for the species. 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. 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). 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. thumb|Nile monitor eating crocodile egg, [[Katavi National Park]]

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.

Distribution and habitat

thumb|[[Lake Manyara National Park, Tanzania]]

Nile monitors are native to Sub-Saharan Africa and along the Nile. They are not found in any of the desert regions of Africa (notably Sahara, Kalahari and much of the Horn of Africa), however, they thrive around rivers.

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. 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. 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, Naranja, and as far south as Key Largo in the Florida Keys.</blockquote>

References

  • Reptiles database
  • Book on the Nile monitor
  • Bibliographical references