The Nile crocodile (Crocodylus niloticus) is a large crocodilian native to freshwater habitats in Africa, where it is present in 26 countries. It is widely distributed throughout sub-Saharan Africa, occurring mostly in the central, eastern, and southern regions of the continent, and lives in different types of aquatic environments such as lakes, rivers, swamps, and marshlands. In West Africa, it occurs along with two other crocodilians. Although capable of living in saline environments, this species is rarely found in saltwater, but occasionally inhabits deltas and brackish lakes. The range of this species once stretched northward throughout the Nile, as far north as the Nile Delta. On average, the adult male Nile crocodile is between in length and weighs including stomach stones. However, specimens exceeding in length and weighing up to have been recorded. It is the largest freshwater predator in Africa, and may be considered the second-largest extant reptile in the world, after the saltwater crocodile (Crocodylus porosus). Size is sexually dimorphic, with females usually about 30% smaller than males. The crocodile has thick, scaly, heavily armoured skin. Nile crocodiles are opportunistic apex predators; a very aggressive crocodile, they are capable of taking almost any animal within their range. They are generalists, taking a variety of prey. Their diet consists mostly of different species of fish, reptiles, birds, and mammals. They are ambush predators that can wait for hours, days, and even weeks for the suitable moment to attack. They are agile predators and wait for the opportunity for a prey item to come well within attack range. Even swift prey are not immune to attack. Like other crocodiles, Nile crocodiles have a powerful bite that is unique among all animals, and sharp, conical teeth that sink into flesh, allowing a grip that is almost impossible to loosen. They can apply high force for extended periods of time, a great advantage for holding down large prey underwater to drown. Nile crocodiles are relatively social. They share basking spots and large food sources, such as schools of fish and big carcasses. Their strict hierarchy is determined by size. Large, old males are at the top of this hierarchy and have first access to food and the best basking spots. Crocodiles tend to respect this order; when it is infringed, the results are often violent and sometimes fatal. Like most other reptiles, Nile crocodiles lay eggs; these are guarded by the females.