One of the questions most asked about snakes, according to Johan Marais of the African Snakebite Institute, is: which one is the most poisonous?
Some plants, like certain mushrooms, are poisonous if eaten. Snakes, on the other hand, are not really poisonous but rather venomous.
Provided you don’t have major lacerations in the throat or open wounds in the stomach, you could safely swallow snake venom without any ill effects. That’s the difference between poisonous and venomous.
Not that I’m suggesting you should try swallowing the venom! Some people may well be allergic to it and go into anaphylactic shock if exposed to it, with dire consequences.
So then the question changes to: which snake is the most venomous? This is quite a debate as the most venomous snake in Africa is not considered particularly dangerous – the boomslang (Dispholidus typus).
Drop for drop, the boomslang has the most potent venom of any snake in Africa. The amount required to kill a human is so small that one could barely see it with the naked eye.
But fortunately the boomslang is extremely reluctant to bite, and seldom does. There are no more than one or two boomslang bites a year in SA, and the victims are often snake handlers, or people who have accidentally stood on the snake.
At home in the trees, the boomslang is extremely reluctant to bite. Stories about it hanging from the branches and biting people as they pass are myths.
Even if you climbed a tree with one or more boomslangs in it, there is virtually no chance that you would be bitten, unless you actually grabbed the snake. Even then, it would be unlikely to bite. If severely provoked, it will inflate its neck. This is the warning sign. Once it does this it will strike out with intent.
The boomslang is back-fanged with short, fixed fangs far back in the mouth. It is often incorrectly said that it can bite only onto a small digit, like a finger. In fact, it can open its mouth very wide, and easily latch onto an arm or a leg.
While most venomous snakes have full control over their venom glands, back-fanged snakes have quite primitive glands and they need to chew on their prey, putting pressure on the venom glands to ensure that it carries along a duct and runs down a groove in the front of each fang. It often happens that a boomslang will bite a chameleon, release it, bite it again and repeat the process a few times. This is to make sure that the venom takes effect.
It is not uncommon for people to be bitten by a boomslang (or any other snake for that matter) without the venom entering their bloodstream. Such bites are called dry bites.
Boomslang venom is haemotoxic, affecting the blood clotting mechanism, and is very slow to take effect. Victims seldom experience serious symptoms in the first few hours and untreated cases may result in human fatalities after 12 hours or even a few days.
There is an anti-venom serum made especially for boomslang bites, and this is kept at the South African Vaccine Producers offices and supplied when required.
To measure the strength of snake venom, we used to rely on a test called an LD 50. Increasing quantities of a specific snake venom would be injected into 100 mice or rats until 50 of them succumbed. The result would then be reflected in milligrams per kilogram of animal. Because of rules on ethics towards animals, these tests are used less often nowadays. One of the problems with such tests is that the effect of the venom may well be very different on humans compared with mice. We know, for instance, that many snakes have prey-specific venoms that are highly effective at killing some prey but have little or no effect on humans.
So perhaps the question should be: what is the deadliest snake? Some of the sea snakes have venom that is far more toxic than those of land snakes, but as few people get bitten by sea snakes, they don’t really feature.
If you did an internet search, you might find that the Australian taipan is rated as one of the deadliest snakes in the world, and this view may well be the result of an LD 50 test. But as most Australian taipans live in the sparsely populated outback, they seldom account for bites and the first human death from a taipan bite occurred very recently. So can you really consider it to be one of the deadliest snakes if it has killed only one person in recent years?
In Africa, where there are about 20 000 snakebite deaths a year, the main culprit is the saw-scaled viper, also known as the carpet viper, of the genus Echis. It has a potent haemotoxic venom, and part of the problem is a lack of anti-venom serums and medical facilities in northern Africa.
In southern Africa, the Mozambique spitting cobra (Naja mossambica) accounts for the majority of serious snakebites, followed by the puff adder (Bitis arietans) and the stiletto snake (Atractaspis bibronii). These three snakes account for more than 80% of our serious snakebites. However, the mortality rate is extremely low as the venoms are cytotoxic, causing severe pain, local swelling and tissue damage but seldom death. Most victims are treated successfully, although some may lose limbs or suffer severe tissue damage.
Our stiletto snakes have not caused any human deaths but those farther north in Africa have done so.
Among our cobras, the Cape cobra (Naja nivea) has the most potent venom and along with the black mamba (Dendroaspis polylepis), accounts for the most human fatalities. Information on snakebite deaths is hard to come by, but there are between 12 and 24 deaths a year in southern Africa. These snakes have predominantly neurotoxic venom that quickly affects the victim’s breathing.
As for the most dangerous snake in Africa, or in the world for that matter, I would go with the black mamba. It is by far the largest, historically reaching 4,5m in length, although specimens of more than 3,8m are unheard of these days.
Because of its size it has a lot of venom. It bites readily, often more than once. The venom is rapidly absorbed and may have a severe effect on breathing within 20 minutes.
Although the black mamba is often labelled an aggressive snake, it is in fact shy and nervous and quick to escape when it can, but if it is cornered or hurt it will not hesitate to strike. One problem is that because of its length the mamba may strike in the chest region and such a bite is far more serious than a bite on an arm or a leg.
Another myth is that there is a “two-step snake” – it bites you, and you die after taking two steps. There is no such snake.
An untreated bite from a black mamba may kill a human in anything from four to 16 hours, and in severe cases within an hour, but that is unusual. Even so, it should be remembered that people have died within minutes of being stung by a bee, or from eating a peanut. There are always exceptions to the rule