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Nile crocodile


     Ancient reptile
     Master predator
     Reproduction of Nile crocodiles
     Crocodile leather
     What people say
     Scientific facts about the Nile crocodile
     References

Ancient reptile


     Nile crocodile (Crocodilus niloticus) an ancient egg laying reptile, preserved to this day despite the planetary cataclysms. Lives in sub-Saharan Africa almost everywhere: in 47 African countries, including Madagascar. Historical records show that previously the habitat of the Nile crocodile extended North to Israel and Algeria.

Nile crocodile

     There is an opinion based on genetic analysis that the existing taxonomy is incorrect, and under the general name "Nile crocodile" there are two species, genetically different from each other: Crocodilus niloticus (Nile crocodile) and Crocodilus suchus (West African crocodile or Desert crocodile).

Exterior markers of Nile crocodile

     Crocodilus niloticus inhabits by seasonal rivers of the plains and savannas of eastern Africa. Crocodilus suchus is smaller and less aggressive; it lives in lagoons and marshes of wooded West and Central Africa. In early historical times, both species could be find in the Nile. Perhaps the smaller and more docile Crocodilus suchus was bred by Egyptian priests for ceremonial purposes.

     In Africa, the Nile crocodile has many names:

     Mamba (Swahili),
     Garwe (Shona),
     Ngwenya (Ndebele),
     Voay (Malagasy),
     Kwena (Tswana),
     Crocodilo (Portuguese),
     Crocodil du Nil (French),
     Temsah (Arabic),
     Denkyem (Twi).

     The Nile crocodile lives in rivers, lakes, swamps, wherever there is fresh and even slightly brackish water. Males are one third larger than females and can reach lengths of 5.5 meters and weights up to 750 kilograms (in exceptional cases 6.5 meters and 1000 kg). In favorable conditions, the Nile crocodile lives up to 100 years.

Nile crocodiles

     Being a cold-blooded animal, the crocodile receives heat from the environment, often crawls out to bask on the shore or in shallow water, where large concentrations of basking crocodiles are often formed. On land, crocodiles move using an asymmetrical gait, which is found only in mammals. Under water, without emerging for breathing, crocodiles can stay 1 hour or even more.

     The Nile crocodile has up to 80 replaceable teeth. Crocodile teeth are rare, and the tongue along the entire length fused with the bottom of the oral cavity. Crocodiles are unable to chew food and they swallow prey in large chunks. To grind food in the stomach crocodiles swallow stones. There is an opinion that crocodiles swallow stones for ballast. In any case, the presence of stones in the stomach leads to the fact that dead crocodiles always sink.

     Crocodile watchman. A small bird, an Egyptian runner, is often seen at the mouth of a crocodile. There is naive statement that the bird cleans the teeth of the crocodile, supposedly taking out the stuck meat from there. Crocodile hardly needs cleaning of the teeth. More credible is the view that flies, which are twining around the jaws of a crocodile,  attract the Egyptian runner.

     Global population of Nile crocodile in the wild is estimated between 250,000-500,000. In Malawi, the population of the Nile crocodile is 8,000-15,000 individuals according to 1987 data.

Master predator


     Nile Crocodile, standing on top of the food chain (master predator), is an omnivorous predator. The menu of the young crocodile is made up of insects. As the crocodile grows, its ration expands at the expense of amphibians, crustaceans, fish, reptiles, and even birds. An adult crocodile can eat large mammals. Crocodiles have good eyesight, smell and hearing, they know how to identify places where animals come to the watering place or cross the river ford. In such places, crocodiles are motionlessly and patiently waiting for their prey.

     Usually crocodile suddenly jumps out from underwater, grabs the victim with his teeth, shakes the victim, quickly rolls it, then drags the victim under the water.

     Turned out with prey in the water, the crocodile uses the method of "deadly rotation" for tearing out from the victim, sometimes still alive, large pieces of meat.

     The Nile crocodile is a problem animal, killing more people and livestock than any other predator in Africa. The problem is exacerbated wherever there is competition between crocodiles and people for water resources. The tactics, adopted by a number of African peoples, to scare away crocodiles with loud cries is a weak means, unable to keep a hungry crocodile from attacking.

     An adult Nile crocodile has a high jaws strength enough to bite off a human leg above the knee or bite through a human skull. Most often, the victims of crocodiles are young men.

     A bite of a crocodile is a relatively common type of injury among people living in the southern part of Malawi, especially near the Shire river. This river is a source of fish and water for the local population. The crocodile bites are usually deep, with significant damage to soft tissues and with bone fractures, infected with pathogenic microflora, which complicates treatment and often leads to the need for amputation of the bitten limb.

     The difference in the body mass of the crocodile and the attacked person by them is a factor that determines the fate of the victim. In the water (swimming, wading a river), a person weighing 75 kilograms has a relatively high probability of survival when he is attacked by a 3-meter crocodile (81% of survivors). The probability of survival is significantly reduced when attacking a 4-meter crocodile (17%), and tends to zero when attacking a crocodile 4.5 meters long (2%). A person in a boat, when he is attacked by a 4-meter crocodile, survives in 73% of cases, being on the coast - in 97% of cases. Using a boat less than 4.5 meters long increases the risk of death several times.

     In winter, crocodiles do not eat for several months. Reptiles are not able to digest food when there is not heat enough. In Malawi, it is cold in May and June (temperatures can fall below 10 degrees Celsius). During this period, the danger of being attacked by a crocodile is much lower. However, without feeling the need for food, the crocodile can attack even in cold weather, if it feels the danger coming from a person.

     A crocodile bites a human shadow. There is a misconception that a crocodile, attacking a man, first tries to bite shadow of the man. In fact, the crocodile is smart enough to be able to distinguish between potential prey and the shadow cast by it.

     Being omnivorous predators, Nile crocodiles are hosts of Trichinella papuae and Trichinella zimbabwensis, dangerous parasites whose larvae affect the muscles.

     The recent discovery (in 1995) of Trichinella zimbabwensis in crocodiles from Zimbabwe, Mozambique and Ethiopia has led to tough control measures to prevent the possible spread of infection in humans. The prevalence of Trichinella infection in the studied wild Nile crocodiles from South Africa is 38.5%.

Reproduction of Nile crocodiles


     Females of the Nile crocodile become sexually mature, reaching the size of 1,8-3 meters. They lay 20 to 60 eggs, weighing 70-110 grams, 6 to 8 centimeters long, on sandy shores between August and March.

     The sex of future newborn crocodiles depends on the temperature at which the eggs ripened. If this temperature was equal to 31.6 degrees Celsius, males will hatch, if the temperature was higher or lower females. The incubation period is 75-95 days. The female Nile crocodile protects the nest (at this time she does not eat anything).

     The female helps the cubs to free themselves from the nests, and also transfers the cubs from the nest to the water, making up to 13 travelings between the nest and the water for 1.5 days. This, taking into account the previous constant care of the nest, indicates a high level of maternal care of Nile crocodiles.

     Young Nile crocodiles begin to make sounds inside the egg and continue to make sounds after hatching. These vocalizations attract the attention of the female. The main vocal frequency of the youngs decreases from the first to the fourth day after hatching. Probably, the tone of sounds produced by newborn crocodiles gives the female information about the age and size of her offspring.

     The main threat to newborn crocodiles is represented by adult crocodiles living nearby, who are not averse to get on breakfast their young nephews. Sometimes only a few cubs survive from the whole nest, the others are eaten.

     Crocodile tears. A metaphor used to describe ostentatious compassion after cruelty towards someone weak and defenseless. Crocodiles have special lacrimal glands washing their eyes. Naturalists, who observed how adult crocodiles eat small individuals of their own species hatched from eggs, attributed the usual work of the lacrimal glands of crocodiles to sadness about the eaten little crocodile babies.

Crocodile leather


     Nile crocodile skin is considered the most valuable of the skin of other crocodile varieties due to the absence of osteoderms (intracutaneous ossifications) on the abdominal side, which can impede dyeing and impair the appearance of leather products.

     In order to get the crocodile leather, which has long become a classic of style, Nile crocodiles are currently bred on farms, mainly in Zimbabwe, South Africa and Zambia, also in Malawi. Up to 160,000 crocodile leathers are produced annually. The development of crocodile farms helps to reduce the illegal sale of leathers, thereby preventing the extermination of the Nile crocodile in its natural habitats.

     The export of crocodile leathers is an important foreign trade activity and a source of Malawi's foreign exchange earnings.

What people say


     We asked villagers in Malawi what they thought of crocodiles. And that is what we heard.

Nile crocodile

     Crocodiles can be used magically to kill a person. This is done with spells. For this purpose, a magical crocodile is needed. A person will be swallowed by a magical crocodile while swimming in the river or even being at own home.

     There are crocodiles created by God, they do not kill people. But the ignorant person will not be able to distinguish between ordinary, magical and God-created crocodiles, all these crocodiles look the same.

     The bile of a crocodile is very poisonous. It is poisonous enough to kill a person. It is prohibited to take the bile from a killed crocodile. In most cases, the police itself take away the crocodile bile, so that no one could use it for magical or other bad purposes.

     Kill a crocodile is not difficult. Crocodiles prefer fresh dog to any other meat. So hunters take a dog, tie it to a tree near the river. As soon as the crocodile rushes on the shore to taste the delicious dog, the hunters come out of ambush and kill the crocodile using rifles.

     If a woman wants to get pregnant, she must keep a stone from the crocodile's stomach in her mouth.

     Seeing a man, the crocodile hisses with anger.

Scientific facts about the Nile crocodile


     Teflon crocodiles. Teflon was found in the blood of wild Nile crocodiles caught in southern Africa. Perfluorinated alkyl acids are the raw materials for the production of chemically and heat-resistant materials (Teflon, fire-fighting foams and the like). Production of perfluorinated alkyl acids began in 1948, these substances are an indicator of anthropogenic environmental pollution, they are found everywhere in the northern hemisphere. A 2016 study found that perfluorinated alkyl acids can also be isolated from the blood of South African crocodiles.

     Crocodile relatives. Genetic analysis proves the similarity of the genome of crocodiles, turtles and birds. Available data suggest a common ancestor of these animals.

     Sensitive crocodile. Crocodiles have sensitive receptors located throughout the entire surface of the body, unlike alligators, in which such receptors are located only on the lower part of the muzzle. Despite the armor, these receptors transmit to crocodile skin the sensitivity that exceeds the sensitivity of the tips of human fingers.

     Death from inflammation of fat. In the Olifants River Gorge in Kruger National Park, South Africa, at least 216 crocodiles was found dead from 2008 to 2012. The cause of the death of crocodiles was pansteatitis, that is, total fat inflammation. The nature of the effect of causing fat inflammation in Nile crocodiles remains in question.

     Crocodiles against cancer. Crocodiles exist in unsanitary conditions, feed on rotten meat, are often exposed to heavy metals such as Arsenic, Cadmium, Cobalt, Chromium, Mercury, Nickel, Lead, Selenium, tolerate high levels of radiation and are among the very few species survived after the catastrophic Cretaceous-Tertiary extinction event. Crocodiles can live up to 100 years. Likely, crocodiles possess mechanisms protection from harmful agents and pathogens. Serum from the organs of the crocodile shows in the experiment a powerful antitumor activity, leading to the death of more than 70% of cancer cells in laboratory samples.

     Salt-resistant Nile crocodile. The acute impact of sea water leads to dehydration of the Nile crocodile, but with a gradual increase in salinity, the crocodile acclimatizes, survives and thrives in sea water.

References


     1. Grigg, G., D. Kirshner. 2015. Biology and evolution of Crocodylians. Ithaca, New York, NY: Cornell University Press.

     2. Hekkala, E., M.H. Shirley, G. Amato, J.D. Austin, S. Charter, J. Thorbjarnarson, K.A.Vliet, et al.. 2011. An ancient icon reveals new mysteries: mummy DNA resurrects a cryptic species within the Nile crocodile. Molecular Ecology 20(20): 4199-215.

     3. Fergusson, R.A. Nile Crocodile Crocodylus niloticus. Pp. 84-89 in Crocodiles. Status Survey and Conservation Action Plan. Third Edition, ed. by S.C. Manolis and C. Stevenson. 2010.

     4. Mphande, J.N.B. 1987. Status of the Nile crocodile in Malawi. Unpub. Report to the Malawi Government.

     5. Caldicott DG, Croser D, Manolis C, Webb G, Britton A. Crocodile attack in Australia: an analysis of its incidence and review of the pathology and management of crocodilian attacks in general. Wilderness Environ Med. 2005;16:143159.

     6. Yusuke Fukuda, Charlie Manolis, Keith Saalfeld, and Alain Zuur. Dead or Alive? Factors Affecting the Survival of Victims during Attacks by Saltwater Crocodiles (Crocodylus porosus) in Australia. PLoS One, v.10(5); 2015

     7. La Grange, Louis J; Marucci, Gianluca; Pozio, Edoardo. Trichinella zimbabwensis in wild Nile crocodiles ( Crocodylus niloticus) of South Africa. Veterinary Parasitology, 2009, Volume 161, Issue 1

     8. Detouf-Boulade, A. (2006). Reproductive cycle and sexual size dimorphism of the Nile crocodile (Crocodylus niloticus) in the Okavango Delta, Botswana. Unpublished MSc Thesis, University of Stellenbosch, South Africa.

     9. Combrink, Xander; Warner, Jonathan K; Downs, Colleen T. Nest predation and maternal care in the Nile crocodile (Crocodylus niloticus) at Lake St Lucia... Behavioural Processes, 12/2016, Volume 133.

     10. Vergne, Am?lie L; Avril, Alexis; Martin, Samuel; Mathevon, Nicolas. Parentoffspring communication in the Nile crocodile Crocodylus niloticus... Naturwissenschaften, 01/2007, Volume 94, Issue 1.

     11. IACTS (2008). World Trade in Crocodilian Skins. UNEPWCMC: Cambridge.

     12. Ian Christie, Jessica L. Reiner, John A. Bowden, Hannes Botha, Theresa M. Cantu, Danny Govender, Matthew P. Guillette, Russell H. Lowers, Wilmien J. Luus-Powell, Danie Pienaar, Willem J. Smit, and Louis J. Guillette. Perfluorinated Alkyl Acids in the Plasma of South African Crocodiles (Crocodylus niloticus). Chemosphere. 2016 Jul; 154: 7278.

     13. Fumio Kasai, Patricia C. M. O'Brien, and Malcolm A. Ferguson-Smith. Reassessment of genome size in turtle and crocodile based on chromosome measurement by flow karyotyping: close similarity to chicken. Biol Lett. 2012 Aug 23; 8(4): 631635.

     14. Duncan B. Leitch and Kenneth C. Catania. Structure, innervation and response properties of integumentary sensory organs in crocodilians. J Exp Biol. 2012 Dec 1; 215(23): 42174230.

     15. Emily P. Lane; Fritz W. Huchzermeyer; Danny Govender; Roy G. Bengis; Peter E. Buss; Markus Hofmeyr; Jan G. Myburgh; Johan C. A. Steyl; Daniel J. Pienaar; Antoinette Kotze. PANSTEATITIS OF UNKNOWN ETIOLOGY ASSOCIATED WITH LARGE-SCALE NILE CROCODILE... Journal of Zoo and Wildlife Medicine, 2013, Volume 44, Issue 4.

     16. Kosta Y. Mumcuoglu. Mortality of Nile Crocodile (Crocodylus niloticus) Eggs Caused by the Flour Beetle (Tribolium castaneum). Open Journal of Veterinary Medicine, 2012, 2, 9-12.

     17. Siddiqui, Ruqaiyyah; Jeyamogan, Shareni; Ali, Salwa Mansoor; Abbas, Fatima; Sagathevan, K.A; Khan, Naveed Ahmed. Crocodiles and alligators: Antiamoebic and antitumor compounds of crocodiles. Experimental Parasitology, 12/2017, Volume 183.

     18. Leslie, Alison J; Spotila, James R. Osmoregulation of the Nile crocodile, Crocodylus niloticus, in Lake St. Lucia, Kwazulu/Natal, South... Comparative Biochemistry and Physiology, Part A, 2000, Volume 126, Issue 3.

        
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