All in There: Balck Mamba

The black mamba (Dendroaspis polylepis) is the longest venomous snake in Africa, averaging around 2.5 meters (8.2 ft), and sometimes growing up to 4.3 meters (14 ft). Apart from being considered one of the world's deadliest snakes, the black mamba is also one of the most feared snakes in Africa due to its potent venom, large size, and the ferocity of its attacks. 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 gray. It is the fastest snake in the world, capable of moving at 4.5 to 5.4 metres per second (16–20 km/h, 10–12 mph).

Taxonomy

The eastern green mamba, Dendroaspis angusticeps, and the black mamba, Dendroaspis polylepis were recognized as one species, until 1946 when Fitzsimon split them into separate species.

Etymology

The snake's scientific name is Dendroaspis polylepis: Dendroaspis meaning "tree asp" and Polylepis meaning "many scaled." The name "black mamba" is given to the snake not because of its body color but because of its ink-black mouth. It displays this physical attribute when threatened.

Description

The black mamba's back skin color is olive, brownish, gray, or sometimes khaki in color. The adult black mamba's length is on average 2.5 meters (8.2 ft), but some specimens have reached lengths of 4.3 to 4.5 meters (14 to 15 ft). Black mambas weigh on average about 1.6 kilograms (3.5 lb). The black mamba is the second longest venomous snake in the world, which is only exceeded in length by the King Cobra. The snake also has an average life span of 11 years in the wild.

Distribution

The black mamba lives in Africa, occupying the following range: Northeast Zaire, southwestern Sudan to Ethiopia, Eritrea, Somalia, Kenya, Eastern Uganda, Tanzania, southwards to Mozambique, Malawi, Zambia, Zimbabwe and Botswana to KwaZulu-Natal in South Africa, and Namibia; then northeasterly through Angola to southeastern Zaire. The black mamba is not commonly found above altitudes of 1000 metres (3280.8 feet), although the distribution of black mamba does reach 1800 metres (5905.5 feet) in Kenya and 1650 metres (5413.3 feet) in Zambia. 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 noted and thus the snake's distribution there is inconclusive.^[6] The black mamba’s distribution contains gaps within the Central African Republic, Chad, Nigeria and Mali. These gaps may lead physicians to misidentify the black mamba and administer an ineffective anti-venom.^[6]

Habitat

The black mamba has adapted to a variety of climates ranging from savanna, woodlands, rocky slopes, dense forests and even humid swamps of Africa. The grassland and savanna woodland/shrubs that extend through central, eastern and southern Africa are the black mamba’s typical habitat.The black mamba prefers more arid environments such as light woodland, rocky outcrops, and semi-arid dry bush country

Environmental Encroachment

The sugarcane fields that dominate the habitat of the black mamba.

The black mamba's environment is rapidly diminishing. In Swaziland alone, 75% of the population is employed by subsistence farming. 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 the snake's territory contributes to potentially dangerous human contact with these venomous snakes.Nearly 20,000 people die of snake bites each year, and the residents of Swaziland and southern Africa have suffered for generations.

Behavior

The black mamba uses its incredible speed to escape threats, not to hunt prey. It is known to be capable of reaching speeds of around 20 kilometers per hour (12 mph), traveling with up to a third of its body raised off the ground Over long distances the black mamba travels 11 to 19 kilometers per hour (6.8 to 12 mph), but in short bursts it can reach a speed of 23 kilometers per hour (14 mph),making it the fastest land snake. It is shy and secretive; it always seeks to escape when confronted. When a black mamba is cornered it mimics a cobra by spreading a neck-flap, exposing its black mouth, and hissing. If this attempt to scare away the attacker fails, the black mamba will strike repeatedly, injecting gratuitous amounts of venom. The black mamba is a diurnal snake. Although its scientific name seems to be indicative of tree climbing, the black mamba is rarely an arboreal snake.

Hunting and Prey

As stated, the black mamba is diurnal. It is an ambush predator that waits for hapless prey to get too close. If the prey attempts to escape, the black mamba will follow up its initial bite with a series of strikes. When hunting, the black mamba has been known to raise a large portion (approximately 48 centimetres or 18 inches) of its body off the ground. The black mamba will release larger prey after biting it, but smaller prey, such as birds or rats, are held onto until the prey's muscles stop moving. Black mambas have been known to prey on bushbabies, bats, and small chickens.

Venom

The venom of the black mamba consists mainly of neurotoxins with an LD50 of 0.25 mg/kg. Its bite delivers about 100–120 mg of venom on average; however, it can deliver up to 400 mg. The mortality rate is nearly 100%, unless the snakebite victim is promptly treated with antivenom. 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 SAIMR (South African Institute for Medical Research) to treat all black mamba bites from different localities.
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. Therefore, calcium levels are unregulated leading to muscular paralysis and eventually death. An example of the potency of the venom is seen through the records of mice. Normally, the death time of a mouse after subcutaneous injection of many toxins is around 7 minutes. However, the black mamba venom killed the mouse in 4.5 minutes.
Because of its highly potent venom, its temperament, and its speed, the black mamba is regarded as one of the most dangerous snakes in Africa. However, humans bitten by a black mamba are rare as the snake would rather avoid confrontation with humans.
If bitten, common symptoms to watch for are rapid onset of dizziness, coughing or difficulty breathing, and erratic heartbeat. In extreme cases, when the victim has received a large amount of venom, death can result within an hour from respiratory or cardiac arrest. Also, the black mamba's venom has been known to cause paralysis. Death is due to suffocation resulting from paralysis of the respiratory muscles.

Predators

The yellow mongoose is just one of the many animals that prey on black mamba eggs.

Mongooses are the main predators of the black mamba. They usually prey on young snakes and eggs. Mongooses are notable due to their resistance to snake toxins. This resistance is caused by mutations in their nicotinic acetylcholine receptor. These mutations prevent the neurotoxin present in snake venom from binding to the receptor, thus preventing the associated toxicity.^[13] Because of the mongoose's resistance to snake venom, adult mambas have trouble fighting them off,^[2] although mongooses seldom attack adult snakes as they are too large for the mammals to kill with ease. Cape file snakes are also predators of young black mambas.^[4]