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 other snakes. Only about 400 of 3,000 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:
- Whom snakes bite: It has been estimated that up to 1.8 million snakebites occur worldwide each year, causing between 20,000 and 94,000 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. About 5 deaths occur per year from snakebites in the United States. People provoke bites by handling or even attacking snakes in a significant number of cases in the U.S. Of the estimated 45,000 snakebites per year in the U.S. about 8,000 are by venomous snakes.
- Which snakes bite: Two major families of snakes account for most venomous snakes dangerous to humans.