[7] A feral population of Nile monitors (descended from escaped or intentionally-released pets) has become established in several locations in South Florida.

[8] 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.

Six years later Leopold Fitzinger moved the Nile monitor into this genus as Varanus niloticus,[11] the currently accepted scientific name for the species.

[12] 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.

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.

[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 bulkier rock monitor.

Nile monitors feed on a wide variety of prey items, including fish, frogs and toads (even poisonous ones of the genera Breviceps and Sclerophrys), small reptiles (such as turtles, snakes, lizards, and young crocodiles), birds, rodents, other small mammals (up to domestic cats and young antelopes [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.

[28][29] 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.

Anecdotal evidence indicates a high rate of disappearance of domestic pets and feral cats in Cape Coral.

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.

Buffrenil (1992) considered that, when fighting for its life, a Nile monitor was a more dangerous adversary than a crocodile of a similar size.

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.