Venom

To most people venom and snakes go hand in hand. It is commonly believed that all snakes are venomous, but this is an erroneous belief. Of the 2.700 known species of snake only 300 are venomous.
So what is venom, how did snakes get it and why do they have it? These are questions that have interested herpetologists and other scientists alike.

Venom itself is a poison secreted by animals for either defensive or offensive purposes. Venom originated from digestive enzymes that were originally located in the stomach. Throughout the millions of years it has progressed quite a lot and in some animals has become quite different from it's origin.
The type of venom depends on the type of animal. In spiders venom is kept rather simple. It is pretty much just digestive enzymes. Spiders use their venom to turn their hard shelled insect meals into nice and nutritious goo. So in a sense one can think of this type of venom as a form of starting the digestive process before you even start to eat the meal.