Venom

Venomous snakes make up only a minority of all snakes. Around 250 species are considered dangerous to humans, i.e. fewer than one tenth of all species, and only about fifty are potentially deadly. They are found in 4 families: the atractaspidids (the burrowing asp, for example), the elapids (cobras, mambas, sea snakes, taipans, etc.), the viperids (vipers, saw-scaled vipers, rattlesnakes, etc.), which are all venomous, and the colubrids (grass snakes, etc.), of which only a third are.

The primary purpose of venom is to kill prey and, to some extent, to prepare digestion through its action on cells, but it can also serve as a defence. To inject it, snakes have a specialised dentition that works somewhat like a hypodermic syringe. These specialised teeth are hollowed out by a groove or a central canal through which the venom flows, and the venom is produced by specific glands. The type of fangs differs from one family to another.

The viperids have the most elaborate dentition. The fangs are folded back when the snake is at rest and straighten up when it opens its mouth, thereby allowing injection. They are sometimes of impressive size (5 cm in the Gaboon viper!), which ensures deep penetration of the venom. The toxicity of the venom varies greatly: some viperids such as Orsini's viper are practically harmless to humans, whereas others such as the saw-scaled vipers are fatal in 90% of cases without treatment.

In the elapids, the fangs are fixed and located at the front of the mouth. Their venom is generally very active and neurotoxic in type. In addition, some elapids such as the spitting cobra can also project their venom several metres, towards the eyes of an opponent, which can cause permanent blindness.

Some colubrid snakes have fangs located at the back of the mouth.

The modes of action of the various venoms are numerous and can, moreover, combine. Firstly, they can affect blood clotting, which can cause internal haemorrhaging. Secondly, they can attack the nervous system, either transiently or permanently. Often the victim dies of asphyxiation, when the paralysis affects the respiratory muscles. Thirdly, the venom can destroy blood vessels and tissues, to the point where the tissues are literally digested down to the bone.

Regardless of the type of dentition and mode of action, the degree of toxicity and the speed of action of the venom are also very varied. Among the species with the most dangerous venom are the Australian taipan and the death adder, two elapids. Another elapid, the king cobra, can cause the death of its victim within 20 minutes. It is one of the few snakes capable of killing an elephant. Among the viperids, the bite of the saw-scaled viper (Echis pyramidum) leads to death in 90% of cases without treatment, and in 70% of cases with treatment.

Treatment of a bite is often based on antivenom serum. But it is not without risks, mainly because of severe allergic reactions. There are also other measures such as local care, particularly when the venom has a tissue-destroying action. In the case of neurotoxic venom, the patient must also be placed on assisted ventilation until they fully recover their respiratory function.

In addition, venomous snakes are able to control the dose of venom they inject, and can deliver a bite that has only a mechanical effect, without a single drop of venom.

In the event of a bite

A venomous snake bite is an emergency, but panic makes things worse: when you become agitated, the heart beats faster and spreads the venom more quickly. The key is to stay calm and to alert the emergency services immediately.