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The most elaborate way of delivering venom has been evolved by yet another family of snakes, the vipers. These include, as well as several different species of viper, such feared creatures as the bushmaster, the fer-de-lance, puff adders and rattlesnakes. The fangs of a king cobra are little more than a centimetre in length. The Gaboon viper (Bitis gabonica), by contrast, which is less than a third of the king cobra’s size, has fangs four times longer. They are so big that if they were fixed in their sockets the snake would be unable to shut its mouth. But they have hinges at their base so that they can fold back and lie, each sheathed in a scabbard of mucous membranes, along the roof of the mouth. Furthermore, a viper can control every element in the movement of its fangs. It can open its mouth until its gape is effectively 180 degrees wide and not even erect its fangs. It can also bite without discharging any venom. And it can bring each fang forwards separately or together. The fangs themselves are shed every six to ten weeks and replaced with new ones that appear alongside the old.
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