Snakes descend from lizards. Like them, they have loosely articulated skulls, and most can dislocate their lower jaw in order to swallow prey much larger than their own head. They differ from legless lizards by their lack of eyelids and external ears.
   Most species are non-venomous. They are generally shy and docile and try to avoid humans. Some are even kept as pets. The venomous snakes use their natural weapon primarily to subdue and kill prey. They are not normally aggressive, but when threatened, they will protect themselves. Its best to avoid them as some have venom powerful enough to cause painful injury or death. This causes many people to fear snakes. North Americans are justified in doing so because there are some really nasty serpents slithering around the countryside.
   This poster presents the most widespread North American species. It makes it easy to tell if a particular snake is a threat, as the graphic design divides them into non-venomous (green background) and venomous (red background) species. It’s the latter you really need to be able to identify, because the others may give you a painful bite, but won’t kill you.