Nile Crocodile (Crocodylus niloticus): Facts and Size

Appearance

Adult Nile crocodiles are dark bronze, olive or grayish above, with darker spots and bands on the back and tail and a dull yellow belly. Mud often hides their true color, and animals from clear, fast rivers tend to be paler than those in murky swamps. Juveniles are greener or browner, with bold dark crossbands that fade with age.

The snout is longer and narrower than an alligator’s but broader than that of slender-snouted species. The mouth holds 64 to 68 cone-shaped teeth, and the enlarged fourth tooth of the lower jaw stays visible when the jaws are closed, as in all true crocodiles. Small pressure-sensitive pits on the scales across the body help it feel ripples made by moving prey. Learn more about these features in alligator vs crocodile.

Size

Males grow considerably larger than females. Most adult males measure 3.5 to 5 m (11.5 to 16.5 ft) and weigh about 150 to 750 kg (330 to 1,650 lb). Females are typically about 30 percent shorter, at 2.2 to 3.8 m (7 to 12.5 ft) and 40 to 250 kg (90 to 550 lb).

Very old males can pass 5.5 m (18 ft) and 1,000 kg (2,200 lb), but such giants are rare. Historical reports include a male from near Mwanza, Tanzania, said to measure 6.45 m (21 ft 2 in), and the famous Burundi crocodile known as Gustave has been estimated at over 6 m (20 ft), although he has never been caught or measured. For how these figures compare with other species, see how big do crocodiles get.

Habitat and range

Nile crocodiles live in almost any large body of fresh water: rivers, lakes, swamps, reservoirs and seasonal pools, usually next to open savanna or woodland. They have working salt glands, so they also enter estuaries, brackish lakes and occasionally the sea. Lake Turkana in Kenya holds one of the largest undisturbed populations.

The species ranges through eastern, central and southern Africa, from the upper Nile basin in Sudan and South Sudan to the Okavango Delta in Botswana and the rivers of South Africa, and into western and southern Madagascar. It once lived along the entire Nile to the Mediterranean, and crocodiles also survived in parts of North Africa and the Levant into historical times, but those populations vanished long ago. In Egypt it survives mainly in Lake Nasser above the Aswan High Dam.

The West African crocodile: a recent split

Until recently, crocodiles across most of Africa were treated as a single species. Genetics changed that. The West African crocodile (Crocodylus suchus) was named in 1807 by the French naturalist Étienne Geoffroy Saint-Hilaire from the skulls of mummified crocodiles, but for nearly two centuries it was treated as just another name for the Nile crocodile. DNA studies published in 2003 and 2011 showed that West and Central African crocodiles form a separate species, and a surprising one: the Nile crocodile is more closely related to the crocodiles of the Americas than to its West African look-alike.

The West African crocodile is smaller, usually 2 to 3 m (6.5 to 10 ft), and is generally calmer around people. It tends to live in lagoons and wetlands in forested regions, and in Mauritania small “desert crocodile” populations survive in rock pools in the Sahara, sheltering in caves and burrows during the driest months. Ancient Egyptians worshipped the crocodile-headed god Sobek and kept, fed and mummified crocodiles at temples such as Kom Ombo, and DNA from mummies shows that many of these sacred animals were West African rather than Nile crocodiles. A 2015 genetic survey of crocodiles labeled as Nile crocodiles in several US zoos found that most were actually West African crocodiles, so older range maps and figures for the “Nile crocodile” often include both species.

Diet and hunting

Nile crocodiles are apex predators that eat almost any animal they can overpower. Hatchlings feed on insects, frogs, crabs and small fish. Fish remain important throughout life, and groups of younger crocodiles sometimes cooperate by forming a semicircle to trap fish against a bank.

Large adults add mammals that come to drink or cross water, such as antelope, zebra, wildebeest and warthogs, along with birds, turtles and carrion. A hunting crocodile drifts toward its target with only its eyes and nostrils showing, then lunges, grips and drags the animal into deep water. Its teeth hold rather than cut, so it tears off pieces by spinning its body, the so-called death roll. Several crocodiles often share one large carcass, and the dominant animals feed first. During the great wildebeest migration, crocodiles gather at crossing points on the Mara River in Kenya and Tanzania, where huge herds must swim across.

Because they are cold-blooded, crocodiles need relatively little food and can go weeks between large meals; a female guarding her nest may not eat for the whole incubation period. Much of what they eat is carrion, and by cleaning up carcasses and keeping populations of predatory fish in check, crocodiles play an important role in African rivers and lakes.

Behavior and social life

Nile crocodiles spend much of the day basking on sandbanks, often with their jaws wide open to help shed heat, and slip into the water when they get too warm. They are more social than many people expect, sharing basking spots and feeding sites under a strict size-based hierarchy in which large, old males dominate.

Most dives last only a few minutes, but a crocodile hiding from danger can stay underwater for around half an hour, and its eyes, ears and nostrils, set high on the head, let it watch and breathe while the rest of the body stays hidden. They communicate with bellows, hisses, snout-slaps on the water and low rumbles. On land they usually crawl on their bellies but can also “high walk” with the body raised, and smaller individuals can gallop. In the southern part of the range, some crocodiles dig burrows and rest inside them through cool, dry spells.

Reproduction, parental care and lifespan

Nile crocodiles reach breeding age at about 12 to 16 years, when males are around 3.3 m (10 ft 10 in) long and females usually 2.2 to 3 m (7 to 10 ft). Males attract females by bellowing, blowing bubbles and slapping their snouts on the water. Unlike the American alligator, which builds a mound of rotting vegetation, the female digs a hole in a sandbank or riverbank during the dry season and buries 25 to 80 eggs. Incubation takes about 90 days, and, as in all crocodilians, nest temperature decides the sex of the young.

The mother guards the nest closely, sometimes with the male nearby. When she hears the hatchlings chirping, she digs them out, may gently crack eggs in her mouth, and carries the babies to the water. The young stay close to her, sometimes in nursery groups, for weeks to many months. Even so, few survive: Nile monitor lizards raid many nests, and hatchlings are eaten by storks, herons, fish eagles, large fish and other crocodiles.

Lifespan is hard to measure in the wild. Large adults are thought to live 50 years or more, but reliable maximum ages are not known.

Predators and threats

Adults have few natural enemies, though hippos are aggressive toward crocodiles and occasionally kill them, and lions occasionally kill crocodiles caught on land. Juveniles also fall prey to large pythons and big cats.

People are the main threat. From the 1940s onward, commercial hunting for leather collapsed many populations; an estimated 3 million Nile crocodiles were killed for their skins between the 1950s and the 1980s. Today the species faces habitat loss from dams, irrigation and wetland drainage, drowning in fishing nets, pollution and killing in retaliation for attacks. In the Olifants River in South Africa’s Kruger National Park, researchers have linked mass crocodile deaths to pollution.

Conservation status

The IUCN Red List classes the Nile crocodile as Least Concern, reflecting strong populations in countries such as Ethiopia, Kenya, Tanzania, Zambia and Zimbabwe. International trade is controlled under CITES, with some populations listed on Appendix I and others on Appendix II, mostly in countries that run regulated ranching programs that collect eggs from the wild and raise crocodiles for leather. Populations in parts of Central Africa are poorly surveyed, and the newly recognized West African crocodile faces fragmented habitat and is less well studied.

Danger to people

The Nile crocodile is the most dangerous crocodilian in Africa. Published estimates suggest hundreds of attacks a year, many of them fatal, though the real number is unknown because many incidents in remote areas are never reported. Most fatal attacks involve crocodiles longer than about 3 m (10 ft) and happen at the water’s edge, where people fetch water, wash, fish or wade. The risk is high mainly because the species lives close to people across much of its range.

Crocodiles usually stay hidden, so the safest approach is to assume they are present in any African river or lake. Stay well back from the water’s edge, follow local and park guidance, never swim or wade where crocodiles live, and keep arms and legs inside boats. If anyone is attacked, call local emergency services and seek emergency medical help immediately.

Myths and facts

Myth: little birds clean crocodiles’ teeth. The ancient Greek historian Herodotus described birds feeding inside crocodiles’ mouths. Field biologists have recorded only rare cases of sandpipers picking leeches and insects off crocodiles, not a regular “toothbrush” partnership.

Myth: crocodiles are always slow. They spend hours motionless, but the lunge from the water takes a fraction of a second.

Myth: all African crocodiles are Nile crocodiles. Africa is also home to the West African crocodile, the slender-snouted crocodiles of West and Central African forest rivers, and the dwarf crocodile, the smallest crocodile species, which rarely grows longer than about 1.9 m (6 ft 3 in).