Snakes use venom to anaesthetise or kill prey and sometimes to help digest it. By using venom, snakes use much less energy to subdue their often much larger quarry and they are less likely to be injured in a struggle.
Venom is produced by modified salivary glands in the mouth. When venomous snakes bite, muscles squeeze the venom out via a duct into each fang, which injects venom into victims.
There is a wide variety of venom among different snake species, but generally venom contains enzymes that digest proteins, which cause animals to go into shock and cause damage to body tissues and internal organs, and/or proteins that affect the functioning of nerves. This leads to paralysis, including stopping breathing and affecting the heart’s beating, which is usually the cause of death.
Unfortunately for people, these venoms have the same effect on us, although snakes mostly bite in self-defence or accidentally because they have been surprised. To counter bites, venom can be milked from snakes to produce anti-venom.
Answered by Dr Andrew Kitchener, principal curator of Vertebrate Biology, National Museums Scotland.