Black mamba
| Black Mamba | |
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| Species: | D. polylepsis
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| Dendroaspis polylepsis | |
The Black mamba (Dendroaspis polylepis) is considered the world’s deadliest snake.[1] The Black mamba is the longest venomous snake in Africa, averaging around 2.5 metres (8.2 ft), and sometimes growing up to 4.3 metres (14 ft). It is one of the most feared snakes in Africa due to its potent venom, large size, and the ferocity of its attacks.[2] Its name is derived from the black coloration inside the mouth; the actual color of the skin varies, from dull yellowish-green to a gun-metal grey. It is one of the fastest snakes in the world, capable of moving at 4.5 to 5.4 metres per second (16–20 km/h, 10–12 mph).[3]
Taxonomy
In the past, the Black mamba was categorized as two subspecies: Dendroaspis polylepis polylepis and Dendroaspis polylepis antinorii. However, due to further research, antinorii was verified as an incorrect subspecies. This invalid claim was made due to other research conducted on the Black mamba’s venom, which concluded that there are varieties in the venom composition of Black mambas from different areas.[3]
Etymology
The snake's scientific name is Dendroaspis polylepis. Dendroaspis means "tree asp." Polylepis means "many scaled."
The name "black mamba" is given to the snake not because of its body color but because of its ink-black mouth.[3]
Description
Despite its name, the Black mamba's skin color is actually olive, brownish, gray, or sometimes khaki in color.[4]The younger Black mambas are lighter, appearing gray or olive green. The Black mamba’s belly is cream-colored, sometimes blended with green or yellow. The Black mamba also appears to have lateral bars running down its body. This effect is from dark spots or blotches that speckle the back half of the body and alternating dark and light scales near the posterior. Their smooth scales are at mid-body, in 23 to 25 rows. The eyes are dark brown to black, with a silvery-white to yellow edge on the pupils. The adult Black mamba's length ranges from 2.0 to 3.0 metres (6.6 to 9.8 ft), with an average length of 2.2 to 2.7 metres (7.2 to 8.9 ft).[5] There have been rare cases of Black Mambas reaching lengths of 4.3 and even 4.5 metres long (14.7 ft). [6] [3] They weigh on average about 1.6 kilograms (3.5 lb).[1] Also, the Black mamba has the most forward pointing fangs of any serpent which is indicative of the family elapidae. [7]
Distribution
The Black mamba lives in Africa, occupying the following range: northeast Zaire, south-western Sudan to Ethiopia, Eritrea, Somalia, Kenya, eastern Uganda, Tanzania, southwards to Mozambique, Malawi, Zambia, Zimbabwe and Botswana to Natal in South Africa, and Namibia; then northeasterly through Angola to southeastern Zaire. [8] Also, the Black mamba is not commonly found above altitudes of 1000 metres (3280.8 feet) ; however, the distribution of black mamba reaches 1800 metres (5905.5 feet) in Kenya and 1650 metres (5413.3 feet) in Zambia.[8] The Black mamba has also been recorded in west Africa in a region of Dakar, Senegal in 1954, but this observation, and a subsequent observation that identified a second specimen in the region in 1956, has not been noted and thus its distribution here is inconclusive. The black mamba’s distribution is filled with gaps in the Central African Republic, Chad, Nigeria, and Mali. These gaps could lead physicians to misidentify the Black mamba and administer an ineffective anti-venom.[8]
Habitat
The grassland and savanna woodland / shrubs that extend through central and western Africa are the Black mamba’s typical habitat. [8] It thrives in the hot and humid environment of the region.[3] It lives on rocky hills, riverine forest with downed trees providing shelter, and wooded-savannah. They have also been known to live in termite mounds and hollow trees.[3]The Black mamba prefers more arid environments such as light woodland, rocky outcrops, and semi-arid dry bush country. [8] The Black mamba is not arboreal, but they can sometimes be found in trees.[3]
Environmental Encroachment
The Black mamba's environment is rapidly diminishing. In Swaziland alone, 75% of the population is employed by subsistence farming.[9] Because of agricultural encroachment on the Black Mamba's habitat, the snake is commonly found in sugarcane fields. The Black mamba will climb to the top of the sugarcane to bask in the sun, and possibly, wait for prey. The majority of human attacks occur in the sugarcane fields, as thousands of workers must plow the fields by hand. This encroachment on its territory contributes to potentially dangerous human contact with venomous snakes. Nearly 20,000 people die of snakes bites each year, and the residents on Swaziland and southern Africa have suffered for generations.[10]
Behavior
The Black mamba spends much of its time basking in a favored sunny spot. They exhibit diurnality, usually active from a few hours after sunrise until about an hour before dusk. [11] [3]They are shy, secretive and will normally retreat from danger.[11] However, this snake will become highly aggressive if it feels threatened, especially if the threat is standing between the snake and its lair.[11] A cornered Black mamba will, while balanced on the rear third of its body, raise its head far off the ground, open its mouth, expand a narrow hood, flick its tongue, open its jaws to reveal the inky black inside of its mouth, and hiss loudly before striking. [11] The strikes will be rapid and numerous. [11] The Black mamba uses its incredible speed to escape threats, not to hunt prey.[1] The Black mamba is capable of reaching speeds up to 20 kilometres per hour (12 mph), traveling with up to a third of its body raised off the ground. [11] The Black mamba are also excellent tree climbers. [11]
Hunting and Prey
The Black mamba's most active hunting month is in October because of the warm spring climates.[11] The Black mamba feeds mostly on small mammals, rodents, squirrels, hyraxes, and occasionally birds.[11] When hunting small animals it delivers a single bite and backs off, waiting for the neurotoxin in its venom to paralyze the prey. However, if the prey is a bird, it will usually hold its bite on the bird waiting for the venom to take effect (lest it fly away and die where the snake cannot find it), the limited supply of venom being diminished without helping the snake survive. The prey is digested by powerful stomach acids in 8 to 10 hours after ingestion. [11] The Black mamba is noted as playing a vital role in controlling rodent populations.[11] At birth, the Black mamba begins to immediately prey on organisms as large as a rat.[7] Though it is not commonly observed the Black mamba may consume termites , as the mounds are commonly used by the Black mamba.[7]
Reproduction
Spring is the Black mamba’s mating season. Black mambas breed once every year.[11]This occurs around September in the African regions. Males will attempt to locate a female by following her scent trail. Once a female is found, the male inspects the female’s body with its tongue. The male Black mamba is equipped with a dual set of penises (hemipenes). If mating is successful the female will lay up to 17 eggs in a nest underground or in a hollow tree. The eggs hatch in about 3 months, during the summer season. During mating season, males will engage in combat. The males fight by coiling around each other; this is often mistaken for mating. The winner will attempt to pin the loser's head to the ground.[11] After mating, the females will lay their eggs during mid-summer. [11] The gestation period is between 80 to 90 days for Black mamba eggs. [11] Black mamba will have from 6 to 17 offspring.[11]
Venom
The venom of the black mamba consists mainly of neurotoxins, with a LD50 of 0.25 mg/kg. [12] Its bites deliver about 100–120 mg of venom on average, however it can deliver up to 400 mg; 10 to 15 mg is deadly to a human.[7] The mortality rate is nearly 100% unless the snakebite victim is promptly treated with antivenom or is put on a respirator or ventilator. It is one of the deadliest snakes in the world. Black mamba bites can potentially kill a human within 20 minutes, but death usually occurs after 30–60 minutes, sometimes taking up to three hours (depending on the health, size, age, psychological state of the human, the penetration of one or both fangs from the snake, amount of venom injected, location of the bite, and proximity to major blood vessels. The health of the snake and the interval since it last used its venom mechanism is also important). Nowadays, there is a polyvalent antivenom produced by SAMIR (South African Institute of Medical Research) to treat all Black mamba bites from different localities.[3]
Because of its highly potent venom, its temperament and its speed, the black mamba is widely regarded as one of the most dangerous snakes in Africa. However, bites from black mambas to humans are rare, as the snakes would rather avoid confrontation with humans.[3][1]
If bitten, common symptoms to watch for are rapid onset of dizziness, coughing or difficulty breathing, and erratic heart-beat.[13] In extreme cases, when the victim has received a large amount of venom, death can result within an hour from respiratory or cardiac arrest.[13] Also, the Black mamba's venom has been known to cause paralysis.[13] Death is due to suffocation resulting from paralysis of the muscles used for breathing. [13]
The Black mamba’s venom is Dendrotoxin. The toxin disrupts the exogenous process of muscle contraction of the sodium potassium pump. First, the toxin causes the release of neurotransmitters at peripheral synapses. Then, the dendrotoxin causes repetitive depolarization in both motor and sensory neurons. This rapid activation of each neuron leads to epileptic activity. Finally, the dendrotoxin blocks potassium channels, stopping the movement of calcium, and therefore calcium levels are unregulated leading to muscular paralysis and eventually death.[7] To understand the potency of the venom, the death time of mice after subcutaneous injection of many toxins is about 7 minutes normally. However, the Black mamba venom killed the mice in 4.5 min. [2]
Predators
Mongooses are the main predators of the Black Mamba. They usually prey on young snakes and eggs. The mongoose is notable due to their resistance to snake toxins. This resistance is due to mutations in the mongoose Nicotinic acetylcholine receptor. These mutations prevent the neurotoxin present in snake venom from binding the receptor and therefore prevent the associated toxicity[14]. Since they have resistance to snake venom, even adult mambas have trouble fighting them off.[15] However, mongooses seldom attack an adult as they are too large for the mammals to kill with ease.
Large reptiles such as crocodiles or monitors, large frogs, foxes or jackals, birds of prey, will also feast on young snakes and primarily eggs. These eggs are also very susceptible to many types of scavengers.
Human beings are the most notable predators. Though humans do not usually consume snakes, they often kill them out of fear.[11]
Gallery
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Black mamba at Wilmington's Serpentarium. -
Close-up of a Black mamba's head -
Close-up of the snake climbing a branch, in London Zoo. -
A Black Mamba at the St Louis zoo.
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References
- ^ a b c d "Black Mamba". National Geographic Society. Retrieved 2010-03-12.
- ^ a b Strydom, Daniel (1971-11-12). "Snake Venom Toxins" (PDF). The Journal of Biological Chemistry. Retrieved 2010-04-24.
- ^ a b c d e f g h i j "Richard Mastenbrok's Elapid Pages".
- ^ Mattison, Chris (1987-01-01). Snakes of the World. New York, New York: Facts on File, Inc. p. 164.
- ^ Smith, Roddy. "Black Mamba Myths and Other Snake Stories". Wildlife Pictures Online. Retrieved 2010-03-04.
- ^ Mattison, Chris (1987-01-01). Snakes of the World. New York, New York: Facts on File, Inc. p. 19.
- ^ a b c d e Shah, Atif. "Black Mamba" (PDF). Sambhota Tibetan Schools Society. Retrieved 2010-05-03.
- ^ a b c d e Håkansson, Thomas (1983-01-01). "On the Distribution of the Black Mamba (Dendroaspis polylepis) in West Africa". Journal of Herpetology. Society for the Study of Amphibians and Reptiles. Retrieved 2010-05-16.
{{cite web}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ "UNDP: Human development indices – Table 3: Human and income poverty (Population living below national poverty line (2000-2007))" (PDF). United Nations Development Programme. 28 November 2008. Retrieved 29 December 2009.
- ^ Litschka-Koen, Thea (2009-11-08). "Antivenom Swazi". Antivenom Swazi Foundation. Retrieved 2010-04-18.
- ^ a b c d e f g h i j k l m n o p q Scott, Randy. "Dendroaspis polylepis". University of Michigan Museum of Zoology Animal Diversity Web. Retrieved 2010-02-28. Cite error: The named reference "Randy" was defined multiple times with different content (see the help page).
- ^ "LD50 Menu". Retrieved 2010-04-21.
- ^ a b c d Davidson, Terence. "IMMEDIATE FIRST AID". Iniversity of California, San Diego. Retrieved 2010-05-12.
- ^ [1]
- ^ The new encyclopedia of Reptiles. 2002.
External links
Media related to Dendroaspis polylepis at Wikimedia Commons