Black mamba
| Black mamba | |
|---|---|
 | |
| A black mamba in defense mode | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Vertebrata |
| Class: | Reptilia |
| Order: | Squamata |
| Suborder: | Serpentes |
| Family: | Elapidae |
| Genus: | Dendroaspis Schlegel, 1848 |
| Species: | D. polylepis |
| Binomial name | |
| Dendroaspis polylepis Günther, 1864[2][3] | |
 | |
| In orange, range of D. polylepis In Green, D. polylepis may or may not occur here | |
| Synonyms[3] | |
| |
The black mamba (Dendroaspis polylepis), also called the common black mamba orblack-mouthed mamba,[4] is the longest venomous snake in Africa, averaging around 2.5 to 3.2 m (8.2 to 10 ft) in length, and sometimes growing to lengths of 4.45 m (14.6 ft).[5] It is named for the black colour of the inside of the mouth rather than the colour of its scales which varies from dull yellowish-green to a gun-metal grey. It is the fastest snake in the world, capable of moving at 4.32 to 5.4 metres per second (16–20 km/h, 10–12 mph).[6] It has a reputation for being aggressive and highly venomous and is among the world's most venomous land snakes based on LD50 on mice in a study.[7]
[edit]
The black mamba was first described in 1864 by Albert Günther, a German-born Britishzoologist, ichthyologist, and herpetologist. Soon after, a subspecies was identified,Dendroaspis polylepis antinorii (Peters, 1873), but this is no longer accepted as distinct.[2][3] The genus and species name are derived from Ancient Greek words -Dendroaspis meaning "tree asp" (dendro is "tree", while aspis is "asp" which is understood to mean a "venomous snake") and polylepis, "many scaled", from poly"many" and lepis "scales".[8][9] The name "black mamba" is given to the snake not because of its body colour but because of the ink-black colouration of the inside of its mouth, which it displays when threatened.[6] In 1896, Boulenger combined the species (Dendroaspis polylepis) as a whole with the eastern green mamba, Dendroaspis angusticeps, and they were considered a single species from 1896[10] until 1946.[11]Taxonomy
It is one of four species in the African snake genus Dendroaspis that are known as mambas.[12]
[edit]Description
The adult black mamba's back skin colour is olive, brownish, gray, or sometimes khaki. A young snake is lighter, but not light enough to be confused with the different species of green mamba. Its underbody is cream-coloured, sometimes blended with green or yellow.[5] Dark spots or blotches may speckle the back half of the body, and some individuals have alternating dark and light scales near the posterior, giving the impression of lateral bars.[12] The inside of the mouth is dark blue to inky black. The head is large but narrow and elongated, with the shape of a coffin.[13][14] It is a proteroglyphous snake, meaning it has immovable, fixed fangs at the front of the maxilla. The eyes are dark brown to black, with a silvery-white to yellow edge on the pupils.[14] These snakes are strong but slender in body: adult specimens are 2.5 to 3 m (8.2 to 9.8 ft) in length on average,[6][15]but specimens measuring 3.1 to 3.75 m (10 to 12.3 ft) are relatively common, and some specimens have reached lengths of 4.3 to 4.5 m (14 to 15 ft).[14][15] The longest scientifically measured, wild-caught black mamba recorded was 4.48 metres (14.7 ft) long and weighed 11.7 kilograms (26 lb), found in Zimbabwe.[16][17] Black mambas weigh about 5.6 kilograms (12 lb) on average, though they can weigh up to 12.5 kilograms (28 lb).[6] There is no real sexual dimorphism, and both male and female snakes of this species have a similar appearance and tend to be similar in size.[18] The species is the second-longest venomous snake in the world, exceeded in length only by the king cobra.[14] Information regarding the lifespan of snakes in the wild is sparse; the longest recorded lifespan of a captive black mamba is 14 years, but actual maximum lifespans could be much greater.[6][19] As they age, their colouration tends to get darker.[12]
[edit]Scalation
There are 23-25 rows of smooth dorsal scales at midbody (rarely 21 rows),[5][12][19] 248-281 ventrals and 109-132 paired subcaudals. The anal shield is divided. There are 7-10 upper labials, with the fourth (or third and fourth) entering the eye, and 11-13 lower labials (sometimes 10 or 14). There are three (sometimes four) preoculars and three or four (sometimes two or five) postoculars. Temporals are variable, usually 2+3.[5]
[edit]Distribution, habitat, and status
[edit]Distribution
Although it is a large diurnal snake, the distribution of the black mamba is the subject of much confusion in research literature, indicating the poor status of African herpetologicalzoogeography.[20] However, the distribution of the black mamba in eastern Africa and southern Africa is well documented. Pitman(1974) gives the following range for the species' total distribution in Africa: northeastern Democratic Republic of the Congo, southwestern Sudan, South Sudan to Ethiopia, Eritrea, Somalia, southern Kenya, eastern Uganda, Tanzania, southwards toMozambique, Swaziland, Malawi, Zambia, Zimbabwe and Botswana to KwaZulu-Natal in South Africa, and into Namibia; then northeasterly through Angola to the southeastern part of the Democratic Republic of Congo.[18][20] According to CITES, the species is found in Lesotho, Rwanda, and Djibouti.[21] The black mamba is not commonly found above altitudes of 1,000 metres (3,300 ft), although the distribution of black mamba does reach 1,800 metres (5,900 ft) in Kenya and 1,650 metres (5,410 ft) in Zambia.[13][20] The black mamba was recorded in 1954 in West Africa in the Dakar region of Senegal.[20] However, this observation, and a subsequent observation that identified a second specimen in the region in 1956, have not been confirmed and thus the species' distribution in West Africa is inconclusive.[20] West of Ethiopia, it has a curious distribution, with few records. There is a single record from the Central African Republic, two from Burkina Faso, and as mentioned two unconfirmed sightings from Senegal, one from the Gambia, and a possible sighting in Cameroon. These sightings may indicate improper documentation, remaining populations from what was once a larger range, or new populations, indicating a growing range.[12] The black mamba's western distribution contains gaps within theCentral African Republic, Chad, Nigeria and Mali. These gaps may lead physicians to misidentify the black mamba and administer an ineffective antivenom.[20]
[edit]Habitat
The black mamba has adapted to a variety of climates, ranging from savanna, woodlands, farmlands, rocky slopes, dense forests and humid swamps.[20] The grassland and savanna woodland/shrubs that extend all the way from southern and eastern Africa to central and western Africa, eastern and southern Africa are the black mamba's typical habitat.[20] The snake prefers more arid environments, such as semiarid, dry bush country, light woodland, and rocky outcrops.[20][22] This species likes areas with numerous hills, as well as riverine forests. Black mambas often make use of abandoned termite mounds and hollow trees for shelter.[22] The abandoned termite mounds are especially used when the snake is looking for somewhere to cool off, as the mounds are sort of a "natural air-conditioning" system. The structure of these mounds is very complex and elaborate. They have a network of holes, ducts, and chimneys that allow air to circulate freely, drawing heat away from the nest during the day - though without taking too much valuable moisture - while preventing the nest cooling too much at night.[18] As a territorial species, though, the black mamba will always return to its territory or lair if left undisturbed.[12][22]
[edit]Conservation status
This species is classified as Least Concern (LC) on the IUCN Red List of Threatened Species (v3.1, 2011). The conservation status of this species was last assessed in 2010 and it was classed as such due to its very large distribution throughout sub-Saharan Africa. Besides its very large geographical distribution, the species has no specific threats or predators that have been reported and this species is not undergoing significant population declines.[1]
[edit]Fear, myths, and killings of black mambas
Adult black mambas have no natural predators or enemies, besides humans.[5] The species faces human persecution because of its negative reputation throughout Africa. With the increasing amount of its territory being inhabited by humans, the black mamba often finds itself cornered with no escape. In this situation, it will stand its ground and display fearsome tenacity and explosive aggression while hissing loudly and striking repeatedly. A group of people is usually required to kill it, as it is very fast and agile, striking in all directions while a third of its body is 3–4 feet (0.91–1.2 m) above the ground. The deep fear of this snake stems not only from its reputation for aggression, speed, and venom toxicity, but from stories and legends that have been passed down from generation to generation.[16]
[edit]Behaviour and ecology
[edit]Behaviour
Although its scientific name seems to be indicative of tree climbing, the black mamba is a terrestrial and diurnal snake.[23] It is known to be capable of reaching speeds of around 20 km/h (12 mph), travelling with up to a third of its body raised off the ground.[6] Over long distances, the black mamba can travel 11 to 19 km/h (6.8 to 12 mph), but it can reach a speed of 16 to 20 km/h (9.9 to 12 mph) in short bursts, and it has been recorded at speeds of 23 km/h (14 mph),[24] making it the fastest land snake in the world.[23] The black mamba is a territorial snake, having a favoured home usually in an abandoned termite mound, a hollow tree or log, or a rock crevice. It will actively defend its territory very aggressively.[25] Although it is a shy and secretive snake in general, it always seeks to escape when a confrontation occurs, unless cornered, in which case the black mamba can put up a fearsome display of defense and aggression.[6] When cornered, it mimics a cobra by spreading a neck-flap; exposing its black mouth, it lifts up to a third of its body up off the ground, and hisses.[6] If the attempt to scare away the attacker fails, it will strike repeatedly.[6] Many snake experts have cited the black mamba as the world's most aggressive snake, noting tendency to actively attack without provocation.[26][27] It can show an incredible amount of tenacity, fearlessness, and aggression when cornered, during breeding season, or when defending its territory.[7]According to Swaziland-born snake handler and snake expert Thea Litschka-Koen:
"black mambas will kill a dog or several dogs if threatened and it happens quite often. We also find dead cows and horses! We were called by the frantic family late one evening. When we arrived minutes later, two small dogs had already died and two more were showing severe symptoms of envenomation. Within 15 minutes we had found and bagged the snake. By this time the other two dogs were also dead. The snake must have been moving through the garden when it was attacked by the dogs. It would have struck out defensively, biting all the dogs that came within reach. The snake was bitten in several places on its body as well and died about a week later."[28]
Similarly, black mambas have been witnessed confronting, biting, and subsequently killing lions and other large predators, such as spotted hyenas and leopards, in defense of their territory, eggs, or when the predators stand between the snakes and their prey.[29]
[edit]Hunting and prey
When hunting, the black mamba is often seen travelling with its head raised well above ground level, quickly moving forward in search of prey. Once prey is detected, the black mamba "freezes" before hurling itself forward and issuing several quick bites, swiftly killing its prey.[24] If the prey attempts to escape, the black mamba will follow up its initial bite with a series of strikes.[24] It will release larger prey after biting it, but smaller prey, such as birds or rats, are held until the prey's muscles stop moving.[24] Black mambas feed on a variety of prey, especially mammals, including hyraxes, rats, mice, squirrels, bats, bushbabies and elephant shrews.[12] They have also been known to prey on birds and small chickens, as well as other snakes, such as the puff adder and Cape cobra.[17] A large specimen has even been recorded eating a young blue duiker (Philantomba monticola).[5] After ingestion, powerful acids digest the prey, sometimes within eight to 10 hours.[5]
[edit]Communication and perception
Black mambas show little deviation from the common methods of communication and perception found in snakes. They use their eyesight mainly for detection of motion, and sudden movements will cause them to strike. The tongue is extended from the mouth to collect particles of air, which are then deposited in the vomeronasal organ on the roof of the mouth, which acts as a chemosensory organ. They have no external ears, but are quite adept at detecting vibrations from the ground. Like many snakes, when threatened, they will display aggression with a set of signals warning of the possibility of attack.[5]
[edit]Reproduction
Black mambas breed only once a year. The breeding season begins in the spring, which occurs around the month of September in the African regions where these snakes occur, as much of sub-Saharan Africa is in the Southern Hemisphere. In this period, the males fight over females.[19] Agonistic behaviour for black mambas involves wrestling matches in which opponents attempt to pin each other’s head repeatedly to the ground. Fights normally last a few minutes, but can extend to over an hour.[30] The purpose of fighting is to secure mating rights to receptive females nearby during the breeding season. Beyond mating, males and females do not interact.[19] Males locate a suitable female by following a scent trail. Upon finding his mate, he will thoroughly inspect her by flicking his forked tongue across her entire body. Males are equipped with two hemipenes.[12] After a successful and prolonged copulation, the eggs develop in the female’s body for about 60 days. During this period, the female seeks a suitable place to lay the eggs. Females prefer using abandoned termite mounds as nests.[30] Mature females lay between 15 and 25 eggs, which they hide very well and guard very aggressively. The eggs incubate for about 60 days before hatching. The hatchlings are about 50 centimetres (20 in) in length and are totally independent after leaving the eggs, hunting and fending for themselves from birth. Young hatchlings are as venomous as the adults, but do not deliver as much venom per bite as an adult snake would.
[edit]Venom
Among mambas, toxicity of individual specimens within the same species and subspecies can vary greatly based on several factors, including geographical region (there can be great variation in toxicity from one town or village to another) and weather.[7] Being a protein of low molecular weight, the venom of the black mamba is rapid-acting. In fact, its venom is the most rapid-acting venom of any snake species[31] and consists mainly of highly potentneurotoxins;[4][32] it also contains cardiotoxins,[25][33] fasciculins,[4] and calciseptine.[34]Subcutaneous LD50 values for this species' venom varies greatly. Ernst and Zug et al. 1996 gave it a value of 0.05 mg/kg,[7] Engelmann and Obst (1981) gave it a value of 0.32 mg/kg,[35] Spawls and Branch list it as 0.28 mg/kg,[12] and Brown gave it a value of 0.12 mg/kg.[36] Although variation is great, the average SC value of the black mamba's venom is said to be around 0.185 mg/kg, making it one of the most venomous land snakes in the world.[7] To illustrate how toxic the venom of this species is, in 2006, a fully grown adult female elephant named Eleanor, who was a matriarch of an entire herd and was between 40 and 48 years of age[37] and weighed over 7,500 pounds (~3,400 kg), was bitten and subsequently killed by a black mamba at Samburu National Reserve in Kenya.[38]Scientists in the field shot footage of the herd calling out in distress and making desperate attempts to get the dying elephant back onto her feet, but Eleanor succumbed to the venom and died.[38] This is the only scientifically verified case of an adult elephant dying of a snakebite.
Although only 10 to 15 mg is deadly to a human adult, its bite delivers about 100–120 mg of venom on average,[12] but as much as 400 mg of venom can be delivered in a single bite.[31] Its bite is often called "the kiss of death" because, before antivenom was widely available, the mortality rate from a bite was 100%.[25][39] Severe black mamba envenomation can potentially kill a human within 20 minutes or less,[6][40] depending on the nature of the bite and the area bitten, but death usually occurs after 30–60 minutes on average, and sometimes taking up to three hours.[13] British wildlife enthusiast Nathan Layton was bitten in Hoedspruit, a small town near Kruger National Park, by a juvenile black mamba, and died less than 30 minutes after being bitten. Nearby ambulance personnel were called to the scene, but Mr. Layton was already dead by the time they had arrived.[41][42] The fatality rate depends on various factors, such as the health, size, age, psychological state of the victim, the penetration of one or both fangs from the snake, amount of venom injected,pharmacokinetics of the venom, location of the bite, and proximity to major blood vessels.[6] The health of the snake and the interval since it last used its venom mechanism is important. Presently, a polyvalent antivenom produced by the South African Institute for Medical Research (SAIMR) is used to treat all black mamba bites from different localities.[12][39] Due to antivenom, a bite from a black mamba is no longer a certain death sentence. But in order for the antivenom therapy to be successful, vigorous antivenom therapy must be administered very rapidly post-envenomation. The doses of antivenom required are often massive (10-12 vials). Cases where 100 cm3of antivenom required is not at all unusual.[12][39]
If bitten, severe neurotoxicity often ensues.[39] Neurological, respiratory, and cardiovascular symptoms rapidly begin to manifest, usually within ten minutes or less. Common symptoms for which to watch are rapid onset of dizziness, drowsiness, coughing or difficulty breathing, convulsions, and an erratic heartbeat.[39] Other common symptoms which come on rapidly include neuromuscular symptoms, shock, loss of consciousness, hypotension, pallor, ataxia, excessive salivation (oral secretions may become profuse and thick), limb paralysis, nausea and vomiting, ptosis, fever, and very severe abdominal pain. Local tissue damage appears to be relatively infrequent and of minor severity in most cases of black mamba envenomation. Edema is typically minimal.[39] In cases where the victim has received larger amounts of venom than average (over 200 mg +) or the venom was delivered right into a vein, death can result within as little as 10 minutes[6][40] from respiratory or cardiac arrest.[39] This is true if the victim is bitten in the face or chest area, as a black mamba can rear up around one-third of its body from the ground, which can put it at about four feet high. When warding off a threat, the black mamba delivers multiple strikes, injecting large amounts of virulently toxic venom with each strike, often landing bites on the body or head, unlike other snakes.[31] The venom of this species has been known to cause permanent paralysis if treatment with antivenom was delayed.[39] Death is due to suffocation resulting from paralysis of the respiratory muscles.[39]
Due to various factors, including the toxicity and high yield of its venom, the fact that untreated bites have a mortality rate of 100%, its high level of aggression, its speed, agility, and size, many herpetologists agree the black mamba is the deadliest and most aggressive snake species in the world.[40] Herpetologists who share this view include Wolfgang Wüster, Charles Pitman, Johan Marais, Vivian FitzSimons, Ray Hunter, and Austin Stevens.[22] Nevertheless, attacks on humans are relatively rare, as the snakes usually avoid confrontation with humans and their occurrence in highly populated areas is not as common as some other African species of venomous snakes.
[edit]Toxins
Mamba venom is made up mostly of dendrotoxins (dendrotoxin-k - "Toxin K",[43] dendrotoxin-1 - "Toxin 1",[44] dendrotoxin-3 - "Toxin 3",[45] dendrotoxin-7 - "Toxin 7",[45] among others), fasciculins, and calciseptine.[34] Being a protein of low molecular weight, the venom and its constituents are able to spread extraordinarily rapidly within the bitten tissue, so black mamba venom is the most rapid-acting of all snake venoms.[31] The dendrotoxins disrupt the exogenous process of muscle contraction by means of the sodium potassium pump. Toxin K is a selective blocker of voltage-gated potassium channels,[43] Toxin 1 inhibits the K+ channels at the pre and postsynaptic level in the intestinal smooth muscle. It inhibits Ca2+-sensitive K+ channels from rat skeletal muscle‚ incorporated into planar bilayers (Kd = 90 nM in 50 mM KCl),[44] Toxin 3 inhibits M4 receptors, while Toxin 7 inhibits M1 receptors.[45] The calciseptine is a 60 amino acid peptide which acts as a smooth muscle relaxant and an inhibitor of cardiac contractions. It blocks K+-induced contraction in aortic smooth muscle and spontaneous contraction of uterine muscle and portal vein.[34] The venom is highly specific and virulently toxic. In one experiment, the death time of a mouse after subcutaneous injection of some toxins studied, was around seven minutes. However, black mamba venom can kill a mouse after 4.5 minutes.[40]
[edit]Situation in Africa
Venomous snakebites are rampant in sub-Saharan Africa.[46] Although antivenom is now widely available and bite victims can rapidly access adequate treatment in most of Africa's medium to large cities and nearby areas,[39] some severely impoverished African nations do not always have antivenom in stock, as it is very expensive, even by Western standards.[47] One example is Swaziland, where the black mamba mortality rate is still very close to 100% because of the lack of antivenom and proper care methods (i.e. mechanical ventilation equipment, proper envenomation symptom control, lack of drugs, etc.). However, Swaziland does have "Antivenom Swazi", which is a charity whose mission is to raise enough funds to create a "bank" of antivenom for treating snakebites, but they are specifically focused on treating black mamba bite victims in Swaziland.[47] Another problem common to most African nations where black mambas occur is bite victims in rural and isolated areas cannot access treatment and therefore have no chance to survive without it. Pockets of areas with a 100% mortality rate due to black mamba envenomation still exist in Africa.[48] However, bites attributed to this species are far less likely compared to most African cobra species and the puff adder. In Tanzania, the black mamba is second only to the puff adder in causing human fatalities, but the puff adder bites almost six times the number of people that the black mamba does.[5][46] 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. From the 900 bites, only 21 ended in fatalities, including all seven black mamba bites - a 100% mortality rate.[49] This and many other studies which resulted in a 100% fatality rate among black mamba bites stimulated the production of a specific mamba antivenom, and in 1967 Louw reported the first successful treatment of two black mamba bites with a specific antivenom prepared by the South African Institute of Medical Research (SAIMR). This was the first time that any victim of a black mamba bite was documented to survive envenomation.[
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