black mamba,the deadly snake ~ half begin

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). Its name is derived from the black colouration inside the mouth; the actual colour 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 Dr. Vivian FitzSimons split them into separate species.^[2]

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 colour but because of its ink-black mouth. It displays this physical attribute when threatened.

Description

The black mamba's back skin colour is olive, brownish, gray, or sometimes khaki in colour^. 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 Democratic Republic of the Congo, 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. 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.

Habitat

The black mamba has adapted to a variety of climates ranging from savanna, woodlands, rocky slopes, dense forests and even humid swamps. 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 of east and southern Africa which employs thousands of workers for manual labour, as cane growing is not a highly mechanised industry. This encroachment on the snake's territory contributes to potentially dangerous human contact with these venomous snakes.

Behaviour

The black mamba uses its speed to escape threats, not to hunt prey.^[1] 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 a confrontation occurs. If 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 large 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 prey to get 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—0.32 mg/kg. Its bite delivers about 100–120 mg of venom on average; however, it can deliver up to 400 mg. The mortality rate from its bites can be 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. (The fatality factor depends 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). Presently, there is a polyvalent antivenom produced by SAIMR (South African Institute for Medical Research) to treat all black mamba bites from different localities.
If bitten, common symptoms for which to watch 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.
The black mamba is one of the most dangerous and feared snakes in Africa due to its potent venom, large size, and the ferocity of its attacks. However, humans bitten by black mambas are rare, as the snake would rather avoid confrontation with humans, and their occurrences are uncommon.

Toxin

The black mamba's venom is dendrotoxin. The toxin disrupts the exogenous process of muscle contraction by means of the sodium potassium pump. 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, a black mamba venom can kill a mouse after 4.5 minutes.