Ornate Monitor

Maximum longevity: 14.6 years (captivity)

In 1975, some north African states replaced the Wild Animals Law created in 1963 with a new law that gives protection to crocodiles, pythons, and monitor lizards. Nile monitors are also listed under the Endangered Species Decree of 1985, which means that international trade of the species in prohibited. This species is listed under CITES, Appendix II.

US Federal List: no special status

CITES: appendix ii

Nile monitors have few predators, but pythons prey on these lizards most often. Young Nile monitors make easy prey for a large python but even larger Nile monitors are at risk. A 4.5 m long African rock python has been reported to seize a 1.4 m long Nile monitor, and within half and hour had swallowed it head first. Crocodiles also take monitors on occasion. A defensive Nile monitor will arch its back and stand at full stretch on its legs, hissing as the body inflates and flicking the tail sideways. As a last resort a cornered Nile monitor will bite savagely and eject foul-smelling matter from the cloaca to deter attack or throw off a pursuer.

Known Predators:

• African rock pythons (Python natalensis)
• Crocodiles

Nile monitors may be Africa's largest lizards, though a former subspecies, now recognized as the species Varanus ornata, may be as big or bigger. Hatchlings are about 30 cm long and weigh about 26 g, but adults may grow to lengths of 2.4 m and have an impressively powerful physique. Sharp claws and strong muscular legs make it easy for them to climb trees. A deep, stoutly constructed skull, blunt crushing posterior teeth, and a bowed lower jaw make it easy for Nile monitors to eat hard-shelled prey such as mollusks. The tough skin is covered by bead-like scales. They have rounded nostrils which are located slightly nearer to the eye than to the snout. The toes are strong and moderately long. The tail of Nile monitors is compressed laterally with a dorsal keel and a very low double-toothed crest.

Adult Nile monitors are brownish or greenish-gray, with darker reticulation and yellowish spots or stripes on the back and limbs and yellowish-green spots on the head. Ventral surfaces are yellowish with blackish cross-bands. Juveniles are black, with the head bearing yellow cross-lines with black and yellow vertical bars on the lips. The neck features yellow lines and the back has a transverse series of yellow spots. The tail of juveniles has alternating black and yellow bars. This species exhibits no sexual dimorphism.

Range length: 2.4 (high) m.

Other Physical Features: heterothermic

Sexual Dimorphism: sexes alike

Estimates vary, but the expected lifespan in captivity is reported at between 10 and 20 years.

Typical lifespan
Status: captivity: 10 to 20 years.

Nile monitors inhabit a wide variety of habitats including woodland, dry savanna, scrub, evergreen thickets, swamps, and mangroves. Nile monitors are usually found near water, either temporary or permanent, but especially rivers, lakes, and pans. Their lifestyle is both terrestrial and aquatic and they are both superb climbers and swimmers which allows for great adaptability to different environments. Exposed, open areas are crucial habitat components as they require sufficient basking locations. This species is known to bask on open rooftops and streets. Young Nile monitors often lie on branches overhanging rivers or pools, and if disturbed will drop into the water. When alarmed and when water is not available, Nile monitors use their sharp claws and strong legs to climb trees up to a height of 5 to 6 meters. They are also known to flee down a hole or rocky crevice, or into a termite nest. Nile monitors live in burrows which they will excavate themselves or expand an existing one. A softer, sandy substrate is necessary to construct these burrows. This species has been documented at elevations from 0 to 1,600 m above sea level.

Range elevation: 0 to 1600 m.

Habitat Regions: temperate ; tropical ; terrestrial ; freshwater

Terrestrial Biomes: savanna or grassland ; scrub forest

Aquatic Biomes: lakes and ponds; rivers and streams; temporary pools

Wetlands: swamp

Other Habitat Features: suburban

Varanus niloticus is found throughout most of sub-Saharan Africa. It is absent from the arid regions of the north and the southwest, but does reach Egypt along the Nile River.

Biogeographic Regions: ethiopian (Native )

Nile monitors are stealthy hunters, concluding their predatory quests by pouncing with lightning speed on their prey. The teeth can administer a painful crushing bite, although this is likely to be lethal to only relatively small victims. While holding an adversary in its jaws, a Nile monitor can cause severe injuries with its claws. They often use a combination of jaws and powerful forelimbs to break the backs of their prey. They eat a variety of prey that includes frogs, toads (even poisonous ones of the genus Breviceps), rodents, fish, lizards, small turtles, birds and their eggs, beetles, orthopterans, crabs, caterpillars, spiders, millipedes, earthworms, and slugs. They have been known to rob crocodile nests for eggs. They may occasionally work in pairs to rob a crocodile nest, with one lizard distracting the guarding mother crocodile while the other races in to grab eggs. Even after hatching, newly emergent crocodiles are not safe. Hard-shelled mollusks are a conspicuous feature of Nile monitors' diets and a thickened skull, blunt crushing teeth, and bowed lower jaw make them well-equipped for breaking open thick shells. Land snails of the genus Achatina are Nile monitors' favorite prey.

Animal Foods: birds; mammals; amphibians; reptiles; fish; eggs; carrion ; insects; terrestrial non-insect arthropods; mollusks; terrestrial worms; aquatic crustaceans

Primary Diet: carnivore (Eats terrestrial vertebrates)

Nile monitors are both predators (on invertebrates and small vertebrates) and scavengers. Their persistent predation on crocodile nests may serve as a control on crocodile numbers.

Termite mounds make a perfect place for Nile monitors to lay their eggs, except during the dry season the hard clay makes it very difficult to burrow in. When the rain comes the females dig holes in the sides of termite mounds and lays their eggs. The termites quickly repair the gaping hole which protects the eggs during development.

Species Used as Host:

• Termites (Eutermes trinervius)

Nile monitors are among the most exploited species of tetrapods in Africa where it is used for food and leather. In certain areas, Nile monitors are hunted to obtain fat from the reproductive organs. It is locally believed that when melted down, this fat is a cure for ear aches as well as a protection against lightning.

Nile monitor lizards consume crocodile eggs and may act as population control in some areas.

Nile monitors are occasionally kept as pets by reptile hobbyists, but these large and aggressive lizards are a poor choice as a pet except perhaps for very experienced keepers who can provide large enclosures.

Positive Impacts: food ; body parts are source of valuable material; source of medicine or drug

Nile monitors have been known to acclimate to human towns, farms, and homesteads, and occasionally attack livestock such as chickens.

Nile monitor eggs may require 10 months of incubation, though eggs in captivity have hatched within as few as 129 days. Within the eggs the embryos are coiled with the snout being forced against the shell wall, ready to rupture the integument and emerge. Hatching takes from 15 minutes to 7 hours. Juveniles lack the crushing and bowed lower jaws of adults, but that most likely reflects the shift from an insectivorous to a molluscivorous diet. Maturity is reached in three to four years. Most wild populations exhibit steady, indeterminate growth throughout their lives, but some heavily exploited populations may undergo significant growth up until 30 months of age and then cease.

Development - Life Cycle: indeterminate growth

Nile monitors use both visual and olfactory cues when sensing the environment. The long forked tongue supplies the vomero-nasal organ in the roof of the mouth. Their eyesight appears to be good. They perceive their environments through visual, tactile, auditory and chemical stimuli.

If cornered, these lizards will inflate the throat and hiss loudly, raise themselves up high, stiff-legged and lash with their tails to threaten the attacker.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: scent marks

Perception Channels: visual ; tactile ; acoustic ; chemical

Nile monitors are sometimes known as "water monitors", or "water leguaan" in South Africa.

Nile monitors are a polygynandrous species and will mate promiscuously. Males may reportedly fight each other in violent "wrestling matches," presumably due to competition for mating opportunities.

Mating System: polygynandrous (promiscuous)

Varanus niloticus breeds once annually, with the season starting in June and ending in October range-wide. Mating and egg laying usually follows the rainy season, which varies regionally. This season correlates with the development of the gonads. The testicles of males are enlarged from June until September while the females are being sought. Regression of the gonads subsequently occurs until January and then the cycle recommences.

After spring rains (August through September), the female excavates a hole in the ground or in an active termite nest and lays 20 to 60 eggs. This may take 2-3 days to complete. If she lays her eggs in a termite nest, the termites will repair the hole in their nest, and the monitor eggs develop inside. Eggs may take up to 1 year to hatch. The small young weigh an average 26 g upon hatching. After hatching, the young may need to wait for rain to soften the hard nest, or reportedly the mother monitor may return at the right time and open the nest to free the hatchlings. Once they have emerged, however, the baby Nile monitors are on their own.

Breeding interval: Varanus niloticus breeds once a year.

Breeding season: Varanus niloticus breeds from June until October.

Range number of offspring: 20 to 60.

Average number of offspring: 35.

Range age at sexual or reproductive maturity (female): 3 to 4 years.

Range age at sexual or reproductive maturity (male): 3 to 4 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; sexual ; fertilization ; oviparous

Parental investment for Nile monitors does not extend far past initial egg fertilization and laying. The female will excavate a secure place to lay her clutch, either in the ground or in an active termite nest. The mother monitor may return to the clutch sometime after the young hatch and open the buried nest to free her hatchlings. Once the young have emerged, however, they are on their own.

Parental Investment: no parental involvement; female parental care ; pre-fertilization (Provisioning, Protecting: Female)

With an almost insatiable appetite, the Nile monitor is renowned for eating just about anything it can overpower or find as carrion. Consequently, its diet includes everything from arthropods, amphibians and fish, to birds, small mammals and other reptiles (2) (3). Hunting strategies vary, but it is rare for the Nile monitor to shy away from a challenge, and will even team up to steal eggs from larger predators such as Nile crocodiles. Whilst one monitor provokes a female crocodile away from a nesting site, another will dig up the unguarded eggs (2). Propelled by its powerful tail, the Nile monitor is an excellent swimmer and reportedly can spend up to one hour submerged (2). Although largely aquatic, the mornings are often spent basking in the sun on rocky outcrops or sandy banks (3). On land, it walks with a sinuous swagger and will sometimes climb trees to bask, feed or sleep (2) (5). However, this species is more vulnerable on land and if threatened will normally do its best to avoid injury and flee to the safety of deep water. When escape is not an easy option, it will boldly defend itself, using its hefty tail, sharp teeth and powerful claws to injure or frighten away the aggressor (2) (3) (5). Following mating, which takes place at the end of the rainy season, the female lays up to 60 eggs (the largest clutch size of any lizard) in termite mounds or burrows (2) (3) (7). Under fairly constant temperature and humidity, the unattended eggs are incubated over a period of six to nine months before hatching (3). The brightly coloured hatchlings survive on a diet comprised almost entirely of insects and reach maturity after three to four years (2).

There are no specific conservation measures in place for the Nile monitor but it is listed on Appendix II of CITES which makes it an offence to trade Nile monitors without a permit (1).

The Nile monitor is not only Africa's largest lizard but also one of the continent's most voracious predators (3). Stout bodied and powerful, this formidable reptile has an elongated snake-like head, sharp claws, and a long, compressed tail which it uses to great effect when under threat (3) (4) (5). The tough, beady skin of the adult is greyish-brown with regular yellow spots arranged in distinctive bands down the head, body and tail. The colour patterning of juveniles is more vibrant, with dark black skin covered in bright yellow spots and blotches (3) (5).

Given its colossal range, it is no surprise that the Nile monitor occurs in a wide variety of habitats, wherever there are permanent bodies of water (6). Although this excludes deserts, this species has been found in most other habitats including grassland, scrub, forests, mangroves, swamps, lakes and rivers (2).

The distribution of the Nile monitor extends through much of sub-Saharan Africa, from Senegal across to Somalia and down to northeast South Africa (2) (5) (6). It also occurs along the Nile up into southern Egypt (2).

Listed on Appendix II of CITES (1).

Although the Nile monitor is exploited for its meat and skin, and to a lesser extent in the pet trade (8), it remains widespread and common (2) (4).

120 to 160 centimeters

Continent: Africa
Distribution: Republic of South Africa, Swaziland, Namibia, Botswana, Tanzania, Mozambique, Zimbabwe, Zambia, Angola, Malawi, Tanzania, Gaon, W/N/S Democratic Republic of the Congo (Zaire), Kenya, Uganda, Cameroon, Central African Republic, Ethiopia, Eritrea, Somalia, Dudan, Chad, Egypt, Liberia, Ivory Coast, Ghana, Togo, Benin, Burkina Faso, Niger, Nigeria, Mali, Mauritania, Senegal, Gambia (HÅKANSSON 1981)
Type locality: œIndiis

Hatchling

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 constitute a valid taxon and are actually polymorphisms of two different species; Varanus stellatus (west African Nile monitor) and Varanus niloticus (Nile monitor). Consequently, Varanus ornatus is considered a synonym of Varanus niloticus and "ornate monitor" is an informal term for forest forms of either species (V. niloticus or V. stellatus). Until 1997, the ornate monitor was considered a subspecies of the Nile monitor. It was subsequently described as a separate species on the basis of reduced number of ocelli rows on the body, a light coloured tongue and a more massive build. More recent work based on a large sample size using mitochondrial and nuclear DNA sequences indicates that Varanus ornatus is not a valid species and that animals with the diagnostic appearance belong either of two sister species of Nile monitor. Animals described as ornate monitor lizards are native to closed canopy forests in West and Middle Africa.