Black mamba

Taxonomy

The black mamba, Dendroaspis polylepis, is an elapid within the genus Dendroaspis. Although it had been known to missionaries and residents, prior to 1860, by the name "mamba", which was already established in the vernacular and taken from the Zulu word "imamba". The first formal description was made by Albert Günther in 1864. In 1873, Wilhelm Peters described two subspecies: the nominotypical D.polylepis polylepis and also D.polylepis antinorii. However, these are no longer held to be distinct. In 1896, Boulenger combined the species (Dendroaspis polylepis) as a whole with the eastern green mamba (Dendroaspis angusticeps), a lumping diagnosis that remained in force until 1946, when FitzSimons split them again into separate species.

The generic name, Dendroaspis, derives from Ancient Greek dendro (δένδρο), meaning "tree", and aspis (ασπίς), which is understood to mean "shield", but also denotes "cobra" or simply "snake", in particular "snake with hood (shield)". Via Latin aspis, it is the source of the English word "asp". In ancient texts, aspis or asp often referred to the Egyptian cobra (Naja haje), in reference to its shield-like hood. Thus, "Dendroaspis" literally means tree asp, reflecting the arboreal nature of most of the species within the genus. The genus was first described by the German ornithologist and herpetologist Hermann Schlegel in 1848. Slowinski et al. (1997) pointed out that the relationships of the African genus Dendroaspis are problematical. However, evidence suggests that Dendroaspis, Ophiophagus, Bungarus, and Hemibungarus form a solid non-coral snake Afro-Asiatic clade.

The specific epithet polylepis is derived from the Ancient Greek poly (πολύ) meaning "many" and lepis (λεπίς) meaning "scale". It apparently refers to the scale count of this species, which is higher than some other species in the genus.

Description

Dendroaspis polylepis is a large, round-bodied, slender, but powerful snake. It tapers smoothly towards the tail, but is of markedly more robust build than its distinctly gracile congeners Dendroaspis angusticeps and Dendroaspis viridis. The head is often said to be "coffin-shaped" with a somewhat pronounced brow ridge and a medium-sized eye. It is a highly proteroglyphous snake, with fangs up to 6.5 millimeters (0.26 in) in length located at the front of the maxilla. The adult snake's length ranges from 2 meters (6.6 ft) to 3 meters (9.8 ft) routinely but, according to some sources, specimens have grown to lengths of 4.3 to 4.5 meters (14.1 to 14.8 ft). Black mambas weigh about 1.6 kilograms (3.5 lb) on average. A specimen of 1.41 meters (4.6 ft) was found to have weighed 651.7 g (1.437 lb). Dendroaspis polylepis is the second longest venomous snake species, exceeded in length only by the king cobra.

Specimens vary considerably in color; some are olive-brown to khaki, many are grey, but none are black. Some individuals display dark mottling towards the posterior, which may appear in the form of oblique bars. The underbody is often pale yellow or cream colored and the eyes are dark brown to black with a silver or pale yellow corona surrounding the pupil. Juvenile snakes are lighter in color than adults, typically grey or olive green in appearance, and they darken with age.

The black mamba has been said to take its name from the color of the inside of its mouth, but this claim is an urban legend, a factoid that lacks objective or historical support. In particular, it was referred to as the "black mamba" decades before knowledge of the color of its oral mucosa was in common circulation. Common names for mambas are to be taken no more seriously than any other common names. We find for example that attempts to impose the more logical common name, "common mamba", for the "black mamba", have been abandoned in favor of applying "common mamba" to the Eastern green mamba, Dendroaspis angusticeps. In the mean time, since the late twentieth century, some authors have unquestioningly copied the claim that the name derived from the color of its open mouth.

Scalation

Like most Elapidae, the scales of the black mamba are smooth and flat, without keels. Most specimens feature 23–25 rows of scales, but rarely as few as 21.

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

Distribution and habitat

The black mamba has a wide and fragmented range within sub-Saharan Africa. Specifically, 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, southwards to Mozambique, Swaziland, Malawi, Zambia, Zimbabwe and Botswana to KwaZulu-Natal in South Africa, and Namibia; then north easterly through Angola to south eastern Democratic Republic of the Congo. 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.

The black mamba was also recorded in 1954 in West Africa, in the Dakar region of Senegal. However, 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. The black mamba is not commonly found at altitudes above 1,000 metres (3,300 ft), although its distribution does reach 1,800 metres (5,900 ft) in Kenya and 1,650 metres (5,410 ft) in Zambia.

The black mamba is primarily terrestrial, but occasionally arboreal, especially where it occurs in forest. Typically it inhabits neglected areas of scrub, termite mounds, abandoned burrows and rock crevices. It is adapted to terrain ranging from savannah and woodland to rocky slopes and dense forests. The black mamba prefers moderately dry environments such as light woodland and scrub, rocky outcrops, and semi-arid dry savannah, to dense forest or arid desert.

Behaviour and ecology

The black mamba is graceful but skittish and often unpredictable. It is agile and can move quickly while being shy and secretive by nature and, like most snakes, avoids threats. In the wild, a black mamba seldom tolerates humans approaching more closely than about 40 meters. When confronted it can display great truculence and is likely to gape in a threat display, exposing its black mouth and flicking its tongue. It also is likely to form a hood by spreading its neck-flap as cobras do. The mamba's hood however, is narrower than that of a typical cobra. The threat display may be accompanied by audible hissing.

During the threat display, any sudden movement by the intruder may provoke the mamba into a series of rapid strikes leading to severe envenomation. Also, the size of the black mamba, plus its ability to raise its head well off the ground, enable it to launch as much as 40% of its body length upwards, so mamba bites in humans quite often are on the upper body. This behaviour also permits the snake to land a strike at unexpectedly long range. The black mamba's reputed readiness to attack is often much exaggerated and usually is provoked by perceived threats, such as blocking its intended retreat, accidentally or otherwise.

Speed

For its slender body, the black mamba is deceptively powerful; it is the fastest moving snake indigenous to Africa, and perhaps the fastest anywhere. It does however, move rather clumsily over soft sand, a surface to which it is not adapted. There have been many unrealistic stories concerning the black mamba's speed, perhaps partly because the slender body exaggerates the impression of speed. These stories include the myth that it can outrun a galloping horse or a running human. On 23 April 1906, on the Serengeti Plains, an intentionally provoked black mamba was recorded at a speed of 11 km/h (6.8 mph), over a distance of 43 m (141 ft). A black mamba would almost certainly not be able to exceed 16 km/h (9.9 mph), and like most reptiles it can maintain such relatively high speeds only for short distances.

Diet

The black mamba is diurnal and chiefly an ambush predator, though it has been recorded as hunting partly by pursuit, such as catching pigeons at a watering hole before they can gain sufficient height to escape. It usually goes hunting from a permanent lair, to which it will regularly return, providing that the hunting is good and it is not disturbed. It hunts mainly by sight and in doing so it commonly will raise much of its length well off the ground. The black mamba does not typically hold onto prey after biting, instead releasing its quarry and waiting for it to succumb to paralysis and die. This however depends on the type of prey; for example, it typically will hold onto a bird till it stops struggling to escape. If prey attempts to escape or defend itself, the black mamba often may follow up its initial bite with a rapid series of strikes to incapacitate and quickly kill its prey. The snake has been known to prey on hyrax and rock hyrax, bushbabies, and bats. The black mamba has a potent digestive system and has been observed to digest prey fully within eight to ten hours.

Predators

Not many predators challenge an adult black mamba although it does face a few threats such as birds of prey, particularly snake eagles. Although all species of snake eagle commonly prey on snakes, there are two species in particular that do so with high frequency, including preying on black mambas. These are the black-chested snake eagle (Circaetus pectoralis) and the brown snake eagle (Circaetus cinereus). The Cape file snake (Mehelya capensis), which is apparently immune to all African snake venoms and preys on other snakes including venomous ones, is a common predator of black mambas (limited only by the size it can swallow). Mongooses, which also are partially immune to venom, and are often quick enough to evade a bite, will sometimes tackle a black mamba for prey. Humans do not usually consume black mambas, but they often kill them out of fear.

Reproduction

Black mambas breed annually and mating occurs in the early spring, when male mambas locate a female by following her scent trail. After finding a potential mate the male will inspect the female by flicking his tongue over her entire body. As in other species of snakes and many other reptiles, fertilization is internal and the intromittent organs of the males are in the form of hemipenes. Females lay clutches of eggs with an incubation period of some 80 to 90 days. Like most snakes female mambas are both oviparous and iteroparous. Egg-laying typically occurs during the middle of summer and egg clutches range from 6 to 17 eggs.

During the mating season rival males may compete by wrestling, not by biting. Opponents attempt to subdue each other by intertwining their bodies and raising their heads high off the ground. Observers have on occasion mistaken such wrestling for mating.

Black mambas are generally solitary, but not strictly so; as a rule they interact very little except in male rivalry during the mating season. However, black mambas are well known to share retreats occasionally, either with other mambas, or sometimes with other species of snakes.

In hatching, mambas break though the egg shell with an egg tooth and are born with fully developed venom glands; capable of inflicting a potentially lethal bite minutes after hatching. The body of the newly hatched snake contains the residues of the egg yolk, and assimilates them to sustain the young snake until it finds its first prey.

Lifespan

There is little information available concerning the lifespan of wild black mambas, but the longest surviving captive example had a recorded lifespan of 11 years. It is possible that wild snakes may live significantly longer than this.

Venom

The venom of the black mamba is extremely toxic, commonly causing collapse in humans within 45 minutes or less from a single bite. Without effective antivenom therapy, death typically occurs in 7–15 hours. The venom is chiefly composed of neurotoxins, specifically dendrotoxin. The black mamba is capable of striking at considerable range and occasionally may deliver a series of bites in rapid succession. Despite its reputation for being highly aggressive, like most snakes, it usually attempts to flee from humans unless threatened or cornered.

The black mamba's venom is composed of neurotoxins (dendrotoxin) and cardiotoxins as well as other toxins such as fasciculins. In an experiment, the most abundant toxin found in black mamba venom was observed to be able to kill a mouse in as little as 4.5 minutes. Based on the murine median lethal dose (LD₅₀) values, the black mamba's toxicity from all published sources is as follows:

Its bites can deliver about 100–120 mg of venom on average and the maximum dose recorded is 400 mg. It is reported that before antivenom was widely available, the mortality rate from a bite was nearly 100%. The bite of a black mamba can potentially cause collapse in humans within 45 minutes, or less. Without effective antivenom therapy, death typically occurs in 7–15 hours. Presently, there is a polyvalent antivenom produced by the South African Institute for Medical Research to treat black mamba bites from many localities, and a new antivenom is currently being developed by the Universidad de Costa Rica's Instituto Clodomiro Picado.

A bite from a black mamba causes initial neurological and neuromuscular symptoms that may commonly include headache and a metallic taste in the mouth, which may be accompanied by a triad of paresthesias, profuse perspiration and salivation. Other symptoms may include ptosis and gradual bulbar palsy. Localised pain or numbness around the bite site is common but not typically severe; therefore, application of a tourniquet proximal to the bite site is feasible and may assist in slowing the onset of prominent neurotoxicity. Without appropriate treatment, symptoms typically progress to more severe reactions such as tachydysrhythmias and neurogenic shock, leading to death by asphyxiation, cardiovascular collapse, or respiratory failure.

Attacks on humans

The black mamba is popularly regarded as the most dangerous and feared snake in Africa; to South African locals the black mamba's bite is known as the "kiss of death". However, attacks on humans by black mambas are rare, as they usually try to avoid confrontation, and their occurrence in highly populated areas is not very common compared with some other species. Additionally, the ocellated carpet viper is responsible for more human fatalities due to snakebite than all other African species combined. 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 a time when effective antivenom was not widely available. Out of more than 900 bites, only 21 ended in fatalities, including all seven black mamba bites.

Reported bite cases

Danie Pienaar, now head of South African National Parks Scientific Services, survived the bite of a black mamba without antivenom in 1998. Although no antivenom was administered, Pienaar was in serious condition, despite the hospital physicians having declared it a "moderate" black mamba envenomation. At one point, Pienaar lapsed into a coma and his prognosis was declared "poor". Upon arrival at hospital Pienaar was immediately intubated, given supportive drug therapy, put on mechanical ventilation and placed on life support for three days, until the toxins were flushed out of his system. He was released from hospital on the fifth day. Pienaar believes he survived for several reasons. In an article in Kruger Park Times he said "Firstly, it was not my time to go." The article went on to state, "The fact that he stayed calm and moved slowly definitely helped. The tourniquet was also essential."

In another case, 28-year-old British student Nathan Layton was bitten by a black mamba and died of a heart attack in less than an hour in March 2008. The black mamba had been found near a classroom at the Southern African Wildlife College in Hoedspruit, where Layton was training to be a safari guide. Layton was bitten by the snake on his index finger while it was being put into a jar, but he didn't realize he'd been bitten. He thought the snake had only brushed his hand. Approximately 30 minutes after being bitten Layton complained of blurred vision. He collapsed and died of a heart attack, nearly an hour after being bitten. Attempts to revive him failed, and he was pronounced dead at the scene.

In a rare case of survival without treatment, American professional photographer Mark Laita was bitten on the leg by a black mamba during a photo-shoot of a black mamba at a facility in Central America. The bite ruptured an artery in his calf, which bled profusely. Laita did not go to the doctor or the hospital, and except for the swollen fang marks giving him intense pain during the night, he was not affected and was fine physically. This led him to believe that either the snake gave him a "dry bite" (meaning without injecting venom) or the heavy bleeding pushed the venom out. Some commenters on the story suggested that it was a venomoid snake (in which the venom glands are surgically removed), but Laita responded that it was not. Only later, he found that he had captured the snake biting his leg in a photograph.