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I remember the first time I encountered a viper in the wild. As I grew up in The Netherlands, the only venomous snake we had was the European viper (Vipera berus) - a small, often light to dark brown snake with a zigzag stripe on its back. These modest snakes are actually one of the most succesfull of all snakes, being one of the most widespread snakes in the world, and the only species found within the Artctic Cycle. Soon I would be finding dozens of them in a few hours, sometimes lying on top of one another, but mostly alone. When picked up, European vipers hiss loudly to show their inconvenience, which can be pretty impressive for such relatively small snakes. Although they have a pretty toxic venom, and one fast bite is enough to inject sufficient amounts of it, they are very economic with it. I remember I was photographing a European viper in The Netherlands, and with great enthusiasim I approached it with the camera making numerous shots of its head and body, while I was sitting on my knees approximately 3 feet from the snake on a sandy trail. I remember saying to myself what a great shots these must be, as I suddenly felt something ticking my hand, and it was the snake. I came to close, and since the hissing did not help the snake get rid of me, it decided to launch himself to that big hand that was holding the camera. But I was lucky, the snake kept his mouth closed and only touched my hand quickly. This snake proved to me what I was knowing all along, snakes don't want to spend venom on us. They need it more to subdue their prey. Only in life threatening situations, might a snake use its venom on a human being. Although some snakes are more reluctant to inject venom than others, this is the trend observed in the lion share of all snakes. I thanked this snake and put it back where I found it.
There are some 300 species of Vipers and pitvipers (Viperidae), spread across Europe, Africa, Asia, the US and South-America. Although most of them are not as fast as cobras and allies (Elapidae), some viperids (term to include vipers and pitvipers) can show immense explosive behavior. Especially lanceheads (Bothrops), large and powerfull pitvipers inhabiting the South-American rainforests, are known for their fierceness. From lying still, looking relaxed on the surface, they can suddenly go mad and start biting everything that is in their way while crawling and jumping nervously towards their threat (often the photographer). When this happens with a 7 foot fer-de-lance (Bothrops asper), this can be quite a scary situation! Not to mention the enormous fangs these animals possess, of which the penetration alone would already would cause tremendous pain and tissue damage. Even without the venom, these fangs are already formidable weapons.
Vipers and pitvipers range in size between one foot (African Namqua Dwarf Adder, Bitis schneideri) to more than 11 feet (South-American bushmaster, Lachesis). Most vipers have a somewhat triangular head that is distinctively wider then the neck. The triangular head shape reveals the position of the venom glands and musculature behind the eye. Most viperids are sit-and-wait predators, contrary to the cobras and allies which are mostly active hunters. Although viperids are not as long as some elapids (king cobra, black mamba), some exceed them in weight. Viperids have a much more stout body then elapids. An adult Gaboon viper (Bitis gabonica) can weigh more than 5 kilos.
Rattlesnakes, lanceheads, bamboovipers, are all examples of pitvipers. The characteristic that distinguishes pitvipers from vipers is the presence of a heat-seeking pit, in between the eye and the nose. This structure is a true evolutionary innovation because it enables the snakes to localize warm objects as their prey, or warm spots to hibernate or bask. The pit consist of an inner and an outer chambers, seperated by a membrane that contains a lot of nerve endings. Infrared radiation from warm blooded prey or warm hibernate or basking spots is picked up by the nerve endings in the membrane and can be localized by the snake. Pitvipers can strike their prey with great accuracy.
A rattlesnake's sound is probably one of the most famous, and perhaps the most feared, sounds from the natural world. The rattle at the end of the tail is composed of segments, probably modified scales, that are added one after another at the tail-base each time a rattlesnake sheds its skin. Babies are born with a button, and lack a functional rattle. The first time a baby rattlesnake sheds its skin a segment is added to the button, resulting in a functional rattle. It is a myth that the rattlesnake's age can be determined by counting the number of segments on the rattle, rattlesnakes lose their rattles often because they grow too long and break off. Although it is often claimed that rattlesnakes evolved their rattles to warn large mammals of their presence (for example, American bisons, Bison bison), a plausible scenario, this theory is not completely waterproof. Most rattlesnakes live in habitats were such grazing herd animals do not occur, and those rattlesnakes that do live in grassland are not considered as primitive species in the evolution of rattlesnakes. Many snakes rattle their tales, which, in between leave litter, can also cause a loud sound comparable to the rattle of a rattlesnake. It might be possible that rattlesnakes evolved their rattle because they lived in places that lacked the material used to produce sound (leave litter). It is off course of no doubt that the rattle evolved as a warning signal, but the big question remaining is the selective pressures that caused this remarkable adaptation. When I was walking over and across rock habitat in Arizona in search for rock rattlesnakes (Crotalus lepidus) and twin-spotted rattlesnakes (C. pricei) I was called by a good friend who was with me. When I came up to him I could already hear a rattlesnake making noise, but I could not see the specimen. He told me that rock rattlesnakes and twin-spotted rattlesnakes are famous for revealing themselves by rattling even before you can even see them. This makes the tracking them down much more easy, but that aside. Why do they do this? At first sight, it seems that this can hardly be evolutionary beneficial. But on the other hand, there are some animals there that like to dig into these rocks for food (black bears, ringtails). A snake would make a nice food item, unless it's venomous off course. These rattlesnakes may reveal themselves to warm blooded animals, to prevent them from digging and probing into the rocky crevices in search for their food. Other rattlesnakes do not usually reveal themselves unless you are really close, or trying to pick them up.
The bushmaster is probably the most famous (or infamous) pitviper. Firstly described as Crotalus mutus, meaning 'silent rattler', it was later given it's own genus, Lachesis. This giant of the Central- and South-American rainforest is truly a rarity. Not only is it seldomly encountered, the longest of the Viperidae (growing over 10 feet), it is also one of the few pitvipers that lay eggs (and the only neo-tropical species that does so). Most vipers and pitvipers bear live young (ovoviviparity), although they lack the connection between embryos and mother as seen in viviparity. These amazing snakes inhabit the rainforests from Nicaragua, south to Central- and South-America to Bolivia and Brazil. These enormous snakes have gigantic quantities of venom, up to 400 mg of dry weight, and can inflict serious bites. Envenomation symptoms include nausea, vomiting, diarrhoea, sweating, lowered blood pressure, lowered heart beat, renal disturbances, shock and oedema, necrosis and pain at the bite site.These symptoms result from haemorrhagic, coagulant and neurotoxic properties of their venoms. But bushmaster venom might also have a useful side, as it is currently investigated on its inhibitory effects against tumor growth and angiogenesis.