There are 4 types of poisonous snakes in the USA. Most species of snakes are nonvenomous and those that have venom use it primarily to kill and subdue prey rather than for self-defense. Some possess venom potent enough to cause painful injury or death to humans. Nonvenomous snakes either swallow prey alive or kill by constriction. Cobras, vipers, and closely related species use venom to immobilize or kill their prey.
The venom is modified saliva, delivered through fangs. Venom, like all salivary secretions, is a pre-digestant that initiates the breakdown of food into soluble compounds, facilitating proper digestion. Even nonvenomous snake bites (like any animal bite) will cause tissue damage.
