Ben Franklin was known for his humor through the tough times. So In 1754, during the French and Indian War, Franklin published his famous woodcut of a snake cut into eight sections. It represented the colonies, with New England joined together as the head and South Carolina as the tail, following their order along the coast. Under the snake was the message "Join, or Die".
By 1775, the snake symbol wasn't just being printed in newspapers. It was appearing all over the colonies: on uniform buttons, on paper money, and of course, on banners and flags.
The snake symbol morphed quite a bit during its rapid, widespread adoption. It wasn't cut up into pieces anymore. And it was usually shown as an American timber rattlesnake, not a generic serpent.