Snakes are remarkable animals, successful on land, in the sea, in forests, in grasslands, in lakes, and in deserts. Despite their sinister reputation, snakes are almost always more scared of you than you are of them. Few snakes, with the occasional exception of king cobras (Ophiophagus hannah) or black mambas (Dendroaspis polylepis), act aggressively toward a human without provocation.
Snakes have no limbs, yet all are meat eaters. They catch prey that includes insects, birds, small mammals, and other reptiles, sometimes including other snakes. Only about 400 of 3000 snake species worldwide inject venom (a poison). Many snakes catch their prey by constriction. In constriction, a snake suffocates its prey by tightening its hold around the chest, preventing breathing or causing direct cardiac arrest. Snakes do not kill by crushing prey. Some snakes grab prey with their teeth and then swallow it whole.
Snakes are cold-blooded. Thus, they are unable to increase their body temperature and stay active when it is cold outside. They are most active at 25-32°C (77-90°F).
- How snakes bite: Snakes that inject venom use modified salivary glands. Venom is a modified form of saliva and probably evolved to aid in chemical digestion. Varying degrees of toxicity also make it useful in killing prey. During envenomation (the bite that injects venom or poison), the venom passes from the venom gland through a duct into the snake's fangs, and finally into its prey. Snake venom is a combination of numerous substances with varying effects. In simple terms, these proteins can be divided into 4 categories:
- Cytotoxins cause local tissue damage.
- Hemotoxins cause internal bleeding.
- Neurotoxins affect the nervous system.
- Cardiotoxins act directly on the heart.
- Who snakes bite: It has been estimated that 5 million snakebites occur worldwide each year, causing about 125,000 deaths. Snakebites are more common in tropical regions and in areas that are primarily agricultural. In these areas, large numbers of people coexist with numerous snakes. Five to ten deaths occur per year from snakebite in the United States. People provoke bites by handling or even attacking snakes in a significant number of cases in the United States. Of the estimated 45,000 snakebites per year in the United States, about 8,000 are by venomous snakes.
- Which snakes bite: Two major families of snakes account for most venomous snakes dangerous to humans.
- The elapid family includes the cobras (; the mambas (; the kraits (Bungarus) of Asia; the coral snakes (Micrurus) of the Americas; and the Australian elapids, which include the coastal taipan (Oxyuranus scutellatus), tiger snakes (Notechis), king brown snake (Pseudechis australis), and death adders (Acanthophis). Highly venomous sea snakes are closely related to the Australian elapids.
- The viper family includes the rattlesnakes (Crotalus) (Western diamondback rattlesnake and timber rattlesnake), moccasins (Agkistrodon), and lance-headed vipers (Bothrops) of the Americas; the saw-scaled vipers (Echis) of Asia and Africa; the Russell's viper (Daboia russellii) of Asia; and the puff adder (Bitis arietans) and Gaboon viper (Bitis gabonica) of Africa.
- Most species of the most widely distributed and diverse snake family, the Colubrids, lack venom that is dangerous to humans. Some species, however, including the boomslang (Dispholidus typus), twig snakes (Thelotornis), the Japanese garter snake (Rhabdophis tigrinus), and brown tree snake (Boiga irregularis), can be dangerous. Other members of this family, including American garter snakes, kingsnakes, rat snakes, and racers, are harmless to humans.