Nile monitor

Description

The Nile monitor is Africa's longest lizard. 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). In an average-sized specimen, the snout-to-vent length will be around 50 cm (1 ft 8 in). 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. 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.

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.

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 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.

Distribution and habitat

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. 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.

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. 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. 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. 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.