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Black mamba

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Black mamba
Dendroaspis polylepis (14).jpg
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Elapidae
Genus: Dendroaspis
Species:
D. polylepis
Binomial name
Dendroaspis polylepis
Black Mamba Range.svg
Distribution range of black mamba
Synonyms[3]

The black mamba (Dendroaspis polylepis) is a species of extremely venomous snake, a member of the family Elapidae native to parts of Sub-Saharan Africa. First formally described by Albert Günther in 1864, it is the second-longest venomous snake after the king cobra; mature specimens generally exceed 2 metres (6.6 ft) and commonly grow to 3 metres (10 ft). Specimens of 4.3 to 4.5 metres (14.1 to 14.8 ft) have been reported. Its skin colour varies from grey to dark brown. Juvenile black mambas tend to be paler than adults and darken with age.

The species is both terrestrial and arboreal; it inhabits savannah, woodland, rocky slopes and in some regions, dense forest. It is diurnal and is known to prey on birds and small mammals, including hyrax and bushbabies. Over suitable surfaces, it can move at speeds up to 16 km/h (9.9 mph) for short distances. Adult black mambas have few natural predators.

In a threat display, the black mamba usually opens its inky-black mouth, spreads its narrow neck-flap and sometimes hisses. It is capable of striking at considerable range and may deliver a series of bites in rapid succession. Its venom is primarily composed of neurotoxins that often induce symptoms within ten minutes, and is often fatal unless antivenom is administered. Despite its reputation as a formidable and highly aggressive species, the black mamba only attacks humans if it is threatened or cornered. It is rated as least concern on the International Union for Conservation of Nature (IUCN)'s Red List of Threatened Species.

Taxonomy[edit]

Although the black mamba had been known to missionaries[4] and residents[5] before 1860, the first formal description was made in 1864 by German-British zoologist Albert Günther,[2][3] who spelt the name Dendraspis polylepis. A single specimen was one of many species of snake collected by John Kirk, a naturalist who accompanied David Livingstone on the 1858–1864 Second Zambesi expedition.[6] This specimen is the holotype and his housed in the Natural History Museum, London.[3] The species' generic name is derived from the Ancient Greek words dendron (δένδρον), "tree", and aspis (ασπίς) "asp", and the specific epithet polylepis is derived from the Ancient Greek poly (πολύ) meaning "many" and lepis (λεπίς) meaning "scale".[7] The term "mamba" is derived from the Zulu word "imamba".[8] In Tanzania, a local Ngindo name is ndemalunyayo ("grass-cutter") because it supposedly clips grass.[9]

In 1873, German naturalist Wilhelm Peters described Dendraspis Antinorii from a specimen in the museum of Genoa that had been killed by Italian explorer Orazio Antinori in what is now northern Eritrea.[10] This was subsequently regarded as a subspecies[3] and is no longer held to be distinct.[2] In 1896, Belgian-British zoologist George Albert Boulenger combined the species Dendroaspis polylepis as a whole with the eastern green mamba (Dendroaspis angusticeps),[11] a lumping diagnosis that remained in force until 1946 when South African herpetologist Vivian FitzSimons again split them into separate species.[12] A 2016 genetic analysis showed the black and eastern green mambas are each others' closest relatives, and are more distantly related to Jameson's mamba (Dendroaspis jamesoni).[13]

Description[edit]

The black interior of the mouth of a black mamba

The black mamba is a long, slender, cylindrical snake with a "coffin-shaped" head with a somewhat pronounced brow ridge and a medium-sized eye.[14][15] The adult snake's length typically ranges from 2 to 3 m (6 ft 7 in to 9 ft 10 in) but specimens have grown to lengths of 4.3 to 4.5 m (14.1 to 14.8 ft).[12][15] It is the second-longest venomous snake species, exceeded in length only by the king cobra.[16] The black mamba is a proteroglyphous (front-fanged) snake, with fangs up to 6.5 mm (0.26 in) in length,[17] located at the front of the maxilla.[16] The tail of the species is long and thin, making up 17–25% of its body length.[14] Black mambas weigh about 1.6 kg (3.5 lb) on average.[18]

Specimens vary considerably in colour between olive, yellowish-brown, khaki and gunmetal but are rarely black. The scales of some individuals may a have a purplish glow. Individuals occasionally display dark mottling towards the posterior, which may appear in the form of diagonal crossbands. Black mambas have greyish-white underbellies and the inside of the mouth is dark bluish-grey to nearly black. Mamba eyes range between greyish-brown to shades of black; the pupil is surrounded by a silvery-white or yellow colour. Juvenile snakes are lighter in colour than adults; these are typically grey or olive green and darken as they age.[17][12][14]

Scalation[edit]

The head, body and tail scalation of the black mamba:[15]

Distribution and habitat[edit]

Juvenile in a tree, Kruger National Park, South Africa

The black mamba inhabits a wide range within sub-Saharan Africa; it has been observed in north-east Democratic Republic of the Congo, south-western Sudan to Ethiopia, Eritrea, Somalia, Kenya, eastern Uganda, Tanzania, Burundi, Rwanda, and south to Mozambique, Swaziland, Malawi, Zambia, Zimbabwe and Botswana to KwaZulu-Natal in South Africa, and Namibia; then north-east across Angola to south-eastern Democratic Republic of the Congo.[17][19]

The black mamba's distribution contains gaps within the Central African Republic, Chad, Nigeria and Mali. These gaps may lead physicians to misidentify black mamba bites and administer an inappropriate antivenom. In 1954 the black mamba was recorded in the Dakar region of Senegal. This observation, and a subsequent observation that identified a second specimen in the region in 1956, has not been confirmed and thus the snake's distribution in this area is inconclusive.[19]

The species prefers moderately dry environments such as light woodland and scrub, rocky outcrops and semi-arid savanna.[19] It also inhabits moist savanna and lowland forests.[15] It is not commonly found at altitudes above 1,000 metres (3,300 ft), although its distribution does include locations at 1,800 metres (5,900 ft) in Kenya and 1,650 metres (5,410 ft) in Zambia.[19] It is rated as a species of least concern on the International Union for Conservation of Nature (IUCN)'s Red List of Endangered species, based on its huge range across sub-Saharan Africa and no documented decline.[1]

Behaviour[edit]

A black mamba in defensive posture

The black mamba is both terrestrial and arboreal. On the ground, it moves with its head and neck raised, and typically uses termite mounds, abandoned burrows, rock crevices and tree cracks as shelter. It may share its lair with other snake species, such as the Egyptian cobra. Black mambas are diurnal; in South Africa, they are recorded to bask between 7–10 am and again from 2–4 pm. They may return daily to the same basking site.[15][14]

Skittish and often unpredictable, the black mamba is agile and can move quickly.[17][15] When it perceives a threat, it retreats into brush or a hole.[15] In the wild, black mambas seldom tolerate humans approaching more closely than about 40 metres (130 ft).[15] When confronted it is likely to engage in a threat display, gaping to expose its black mouth and flicking its tongue.[17] It also is likely to hiss and spread its neck-flap.[18][17][15]

During the threat display, any sudden movement by the intruder may provoke the snake into performing a series of rapid strikes, leading to severe envenomation.[15] The size of the black mamba and its ability to raise its head a large distance from the ground enable it to launch as much as 40% of its body length upwards, so mamba bites to humans may occur on the upper body.[17][15] The black mamba's reputation for being ready to attack is exaggerated; it is usually provoked by perceived threats such as the blocking of its movements and ability to retreat.[17] The species' reputed speed has also been exaggerated; It cannot move more quickly than 16 km/h (9.9 mph).[14]

Reproduction and lifespan[edit]

Male black mambas engaged in combat

The black mamba's breeding season and takes place between September and February.[20] following the drop in temperature which occurs from April to June.[12] Rival males compete by wrestling; attempting to subdue each other by intertwining their bodies and wrestling with their necks. Some observers have mistaken this for courtship.[15][14] During mating, the male will slither over the dorsal side of the female while flicking his tongue. The female will signal its readiness to mate by lifting its tail and staying still. The male will then coil itself around the posterior end of the female and align its tail ventrolaterally with the female's. Intermission may last longer than two hours and the pair remain motionless apart from occasional spasms from the male.[12]

The black mamba is oviparous; the female lays a clutch of 6–17 eggs.[15] The eggs are oval-shaped and elongated, measuring 60–80 mm (2.4–3.1 in) long and 30–36 mm (1.2–1.4 in) in diameter. When hatched, the young range from 40–60 cm (16–24 in) in length. They may grow quickly, reaching 2 m (6 ft 7 in) after their first year. Like the adults, juvenile black mambas can be deadly.[15][17] The black mamba is recorded to live up to 11 years, possibly longer.[18]

Feeding[edit]

The black mamba usually hunts from a permanent lair, to which it will regularly return if there is no disturbance. It mostly preys on birds, particularly nestlings and fledglings, and small mammals like rodents, bats, hyraxes and bushbabies. They generally prefer warm-blooded prey but will also consume other snakes. The black mamba does not typically hold onto its prey after biting; rather it releases its quarry and waits for it to succumb to paralysis and death. The snake's potent digestive system has been recorded to fully digest prey eight-to-ten hours.[15][17][12][14]

Adult mambas have few natural predators aside from birds of prey. Young snakes have been recorded as prey of the Cape file snake.[12] Mongooses, which have some resistance to mamba venom and are often quick enough to evade a bite, will sometimes take a black mamba for prey.[21][22][23]

Venom[edit]

The black mamba is the most feared snake in Africa because of its size, aggression, toxicity and speed of onset of symptoms,[20] and is classified as a snake of medical importance by the World Health Organization.[24] [a] A survey of snakebites in South Africa from 1957 to 1963 recorded over 900 venomous snakebites, but only seven of these were confirmed black mamba bites; at that time no effective antivenom was widely available. Of more than 900 bites, only 21 ended in fatalities, including all seven black mamba bites.[26] The peak period for deaths is the species' breeding season, during which black mambas are most irritable.[20] Bites are very rare outside Africa; snake handlers and enthusiasts are the usual victims.[27]

Black mamba venom does not contain protease enzymes; its bites do not generally cause local swelling or necrosis, and a tingling sensation in the bitten area might be the only initial symptom. The snake tends to bite repeatedly and let go, so there might be multiple puncture wounds.[20] Its bite can deliver about 100–120 mg of venom on average; the maximum recorded dose is 400 mg.[28] The murine median lethal dose (LD50) when administered intravenously has been calculated at 0.32[29] and 0.33 mg/kg.[30] Bites were very often fatal before antivenom was widely available.[31]

The venom is predominantly neurotoxic; symptoms often become apparent within ten minutes.[20] Early neurological symptoms that indicate a severe course include metallic taste, ptosis and gradual bulbar palsy.[32] Other neurological symptoms include miosis, blurred or diminished vision, paresthesia, dysarthria, dysphagia, dyspnea, difficulty handling oral secretions, an absent gag reflex, fasciculations, ataxia, vertigo, drowsiness and loss of consciousness, and respiratory paralysis.[20] Other more general symptoms include nausea and vomiting, abdominal pain, diarrhoea, sweating, salivation, goosebumps and red eyes.[31] The bite of a black mamba can cause collapse in humans within 45 minutes or less.[33] Without appropriate antivenom treatment, symptoms typically progress to respiratory failure, which leads to cardiovascular collapse and death.[20] This typically occurs in 7 to 15 hours.[28]

In 2015, the proteome (complete protein profile) of black mamba venom was assessed and published, revealing 41 distinct proteins and one nucleoside.[31] The venom is composed of two main families of toxic agents, dendrotoxins (I and K) and (at a slightly lower proportion) three-finger toxins.[30] Dendrotoxins are akin to kunitz-type protease inhibitors that interact with voltage-dependent potassium channels, stimulating acetylcholine and causing an excitatory effect,[31] and are thought to cause symptoms such as sweating.[20] Member of the three-finger family include alpha-neurotoxin, cardiotoxins, fasciculins and mambalgins.[30] The most toxic components are the alpha-neurotoxins,[31] which bind nicotinic acetylcholine receptors and hence block the action of acetylcholine at the postsynaptic membrane and cause neuromuscular blockade and hence paralysis.[20][31] Fasciculins are anticholinesterase inhibitors that cause muscle fasciculation.[20] The venom has little or no haemolytic, haemorrhagic or procoagulant activity.[20] Mambalgins act as inhibitors for acid-sensing ion channels in the central and peripheral nervous system, causing a pain-inhibiting effect. There is research interest in their analgesic potential.[34]

The composition of black mamba venom differs markedly from those of other mambas, all of which contain predominantly three-finger toxin agents. It is thought this may reflect the preferred prey items—small mammals for the mainly land-dwelling back mamba versus birds for the predominantly arboreal other mambas. Unlike many snake species, black mamba venom has little phospholipase A2 content.[30]

A black mamba swallowing prey

Treatment[edit]

Standard first aid treatment for any suspected bite from a venomous snake is the application of a pressure bandage to the bite site, minimisation of movement of the victim and conveyance to a hospital or clinic as quickly as possible. The lethal, neurotoxic nature of black mamba venom means an arterial tourniquet may be of benefit.[32] Tetanus toxoid is given, though the main treatment is the administration of the appropriate antivenom.[35]A polyvalent antivenom produced by the South African Institute for Medical Research is used to treat black mamba bites from many localities,[36] and a new antivenom is being developed by the Universidad de Costa Rica's Instituto Clodomiro Picado.[37]

Notes[edit]

  1. ^ The ocellated carpet viper is responsible for more human fatalities due to snakebite than all other African species combined.[25]

References[edit]

  1. ^ a b Spawls, Stephen (2010). "Dendroaspis polylepis". IUCN Red List of Threatened Species. 2010: e.T177584A7461853. doi:10.2305/IUCN.UK.2010-4.RLTS.T177584A7461853.en. Retrieved 28 November 2017.
  2. ^ a b c "Dendroaspis polylepis". Integrated Taxonomic Information System. Retrieved 12 December 2013.
  3. ^ a b c d Uetz, Peter; Hallermann, Jakob. "Dendroaspis polylepis Günther, 1864". Reptile Database. Zoological Museum Hamburg. Retrieved 10 September 2018.
  4. ^ Mason, G. H. (1862). Zululand, a mission tour in South Afrika [Africa]. London: J. A. Nisbet. p. 183.
  5. ^ Hawes, William (1859). "On the Cape Colony, its products and resources". Journal of the Society of Arts. 7: 244–257 [252].
  6. ^ Günther, Albert (1864). "Report on a collection of reptiles and fishes made by Dr. Kirk in the Zambesi and Nyassa Regions". Proceedings of the Zoological Society of London. 1864: 303–314 [310].
  7. ^ Liddell, Henry George; Scott, Robert (1980). A Greek-English Lexicon (Abridged ed.). Oxford, United Kingdom: Oxford University Press. pp. 109, 154, 410, 575. ISBN 978-0-19-910207-5.
  8. ^ "Definition of mamba in English". Oxford Dictionaries. OED. Retrieved 11 January 2017.
  9. ^ Loveridge, Arthur (1951). "On reptiles and amphibians for Tanganyika Territory collected by C.J. P. Ionides". Bulletin of the Museum of Comparative Zoology at Harvard College. 106: 175–204 [201].
  10. ^ Peters, Wilhem Carl Hartwig (1873). "Über zwei Giftschlangen aus Afrika und über neue oder weniger bekannte Gattungen und Arten von Batrachiern". Monatsberichte der Königlichen Preussische Akademie des Wissenschaften zu Berlin. Jahre 1873 (1874): 411–418.
  11. ^ Boulenger, George Albert (1896). Catalogue of the snakes in the British Museum (Natural History). London, United Kingdom: Printed by order of the Trustees British Museum (Natural History). Department of Zoology. p. 437.
  12. ^ a b c d e f g Haagner, G. V.; Morgan, D. R. (1993). "The maintenance and propagation of the Black mamba Dendroaspis polylepis at the Manyeleti Reptile Centre, Eastern Transvaal". International Zoo Yearbook. 32 (1): 191–196. doi:10.1111/j.1748-1090.1993.tb03534.x.
  13. ^ Figueroa, A.; McKelvy, A. D.; Grismer, L. L.; Bell, C. D.; Lailvaux, S. P. (2016). A species-level phylogeny of extant snakes with description of a new colubrid subfamily and genus. PLoS ONE. 11. pp. e0161070. Bibcode:2016PLoSO..1161070F. doi:10.1371/journal.pone.0161070. ISBN 978-0-643-10674-1. PMC 5014348. PMID 27603205.
  14. ^ a b c d e f g Spawls, Stephen; Howell, Kim; Drewes, Robert; Ashe, James (2017). A Field Guide to the Reptiles of East Africa (2nd ed.). Bloomsbury. pp. 1201–1202. ISBN 978-1-4729-3561-8.
  15. ^ a b c d e f g h i j k l m n o Marais, Johan (2004). A complete guide to the snakes of southern Africa (New ed.). Cape Town: Struik. pp. 95–97. ISBN 978-1-86872-932-6.
  16. ^ a b Mattison, Chris (1987). Snakes of the World. New York: Facts on File, Inc. pp. 84, 120. ISBN 978-0-8160-1082-0.
  17. ^ a b c d e f g h i j FitzSimons, Vivian F. M. (1970). A Field Guide to the Snakes of Southern Africa (Second ed.). HarperCollins. pp. 167–169. ISBN 978-0-00-212146-0.
  18. ^ a b c "Black mamba". National Geographic Society. 10 September 2010. Retrieved 3 December 2010.
  19. ^ a b c d Håkansson, Thomas; Madsen, Thomas (1983). "On the Distribution of the Black Mamba (Dendroaspis polylepis) in West Africa". Journal of Herpetology. 17 (2): 186–189. doi:10.2307/1563464. JSTOR 1563464.
  20. ^ a b c d e f g h i j k Hodgson, Peter S.; Davidson, Terence M. (1996). "Biology and treatment of the mamba snakebite". Wilderness and Environmental Medicine. 2 (2): 133–145. PMID 11990107.
  21. ^ "Watch a Mongoose Swing From a Deadly Snaked". National Geographic Society. 3 October 2017. Retrieved 7 September 2018.
  22. ^ "Mongoose Vs. Snake – Nat Geo Wild". Nat Geo Wild. Retrieved 7 September 2018.
  23. ^ Tsetlin, V. I. (2001). "Snake venom α‐neurotoxins and other 'three‐finger' proteins". European Journal of Biochemistry. 264 (2): 281–286. doi:10.1046/j.1432-1327.1999.00623.x.
  24. ^ WHO Expert Committee on Biological Standardization. "Guidelines for the production, control and regulation of snake antivenom immunoglobulins" (PDF). WHO Technical Report Series, No. 964. pp. 224–26. Retrieved 1 January 2019.
  25. ^ Walls, Jerry G. "The World's Deadliest Snakes". Reptiles. Retrieved 9 December 2018.
  26. ^ O'Shea, M. (2005). Venomous Snakes of the World. United Kingdom: New Holland Publishers. p. 78. ISBN 978-0-691-12436-0. ... in common with other snakes they prefer to avoid contact; ... from 1957 to 1963 ... including all seven black mamba bites – a 100 per cent fatality rate
  27. ^ Závada, J.; Valenta, J.; Kopecký, O.; Stach, Z.; Leden, P. (2011). "Black Mamba Dendroaspis Polylepis Bite: A Case Report". Prague Medical Report. 112 (4): 298–304. PMID 22142525.
  28. ^ a b Branch, Bill (1988). Field Guide to the Snakes and Other Reptiles of Southern Africa. London: New Holland. p. 95. ISBN 978-1-85368-112-7.
  29. ^ Harrison, Robert A.; Oluoch, George O.; Ainsworth, Stuart; Alsolaiss, Jaffer; Bolton, Fiona; Arias, Ana-Silvia; Gutierrez, Jose-Maria; Rowley, Paul; Kalya, Stephen; Ozwara, Hastings; Casewell, Nicholas R. (2017). "Preclinical antivenom-efficacy testing reveals potentially disturbing deficiencies of snakebite treatment capability in East Africa". PLOS Neglected Tropical Diseases. 11 (10). doi:10.1371/journal.pntd.0005969.
  30. ^ a b c d Ainsworth, Stuart; Petras, Daniel; Engmark, Mikael; Süssmuth, Roderich D.; Whiteley, Gareth; Albulescu, Laura-Oana; Kazandjian, Taline D.; Wagstaff, Simon C.; Rowley, Paul; Wüster, Wolfgang; Dorrestein, Pieter C.; Arias, Ana Silvia; Gutiérrez, José M.; Harrison, Robert A.; Casewell, Nicholas R.; Calvete, Juan J. (2018). "The medical threat of mamba envenoming in sub-Saharan Africa revealed by genus-wide analysis of venom composition, toxicity and antivenomics profiling of available antivenoms". Journal of Proteomics. 172: 173–189. doi:10.1016/j.jprot.2017.08.016.
  31. ^ a b c d e f Laustsen, Andreas Hougaard; Lomonte, Bruno; Lohse, Brian; Fernandez, Julian; Maria Gutierrez, Jose (2015). "Unveiling the nature of black mamba (Dendroaspis polylepis) venom through venomics and antivenom immunoprofiling: Identification of key toxin targets for antivenom development". Journal of Proteomics. 119: 126–142. doi:10.1016/j.jprot.2015.02.002. PMID 25688917.
  32. ^ a b Dreyer, S. B.; Dreyer, J. S. (November 2013). "Snake Bite: A review of Current Literature". East and Central African Journal of Surgery. 18 (3): 45–52. ISSN 2073-9990.
  33. ^ Visser, J; Chapman, D. S. (1978). Snakes and Snakebite: Venomous snakes and management of snake bite in Southern Africa. Purnell. p. 52. ISBN 978-0-86843-011-9.
  34. ^ Diochot, Sylvie; Baron, Anne; Salinas, Miguel; Douguet, Dominique; Scarzello, Sabine; Dabert-Gay, Anne-Sophie; Debayle, Delphine; Friend, Valérie; Alloui, Abdelkrim (2012). "Black mamba venom peptides target acid-sensing ion channels to abolish pain". Nature. 490 (7421): 552–555. Bibcode:2012Natur.490..552D. doi:10.1038/nature11494. ISSN 0028-0836. PMID 23034652.
  35. ^ Gutiérrez, José María; Calvete, Juan J.; Habib, Abdulrazaq G.; Harrison, Robert A.; Williams, David J.; Warrell, David A. (2017). "Snakebite envenoming". Nature Reviews Disease Primers. 3 (3): 17063. doi:10.1038/nrdp.2017.63. PMID 28905944.
  36. ^ Davidson, Terence. "Immediate First Aid". University of California, San Diego. Retrieved 12 May 2010.
  37. ^ Sánchez, Andrés (2017). "Expanding the neutralization scope of the EchiTAb-plus-ICP antivenom to include venoms of elapids from Southern Africa". Toxicon. 125: 59–64. doi:10.1016/j.toxicon.2016.11.259. PMID 27890775.

External links[edit]

Media related to Dendroaspis polylepis at Wikimedia Commons