Why do worm come to the surface when it rains? ~ Lansing
Most of the earthworms found in North America today did not exist prior to European settlement. They were imported mainly from Europe by early settlers. The worms or worm cocoons traveled in the rootstocks of plants brought by the settlers from their homelands. They were also released into the new world through soil that was used for ship ballast that was discarded after the voyage to the new world.
Worms are food for lots of animals like rodents, snakes, toads, and of course birds. They make up about 15%-20% of the summer diet for American Robins who hunt earthworms by cocking their head to one side, independently using each eye to look for visible signs of worms. Robins round out their diet with other insects, fruit, nuts, and berries.
Learn more about Earthworms at: http://www.learner.org/jnorth/tm/worm/WormLife.html