According to a page on the University of Illinois Extension educational website:
"Worms help to increase the amount of air and water that gets into the soil. They break down organic matter, like leaves and grass into things that plants can use. When they eat, they leave behind castings that are a very valuable type of fertilizer."I'll take a worm doing its magic over the spraying of pesticides any day of the week.
Watch a worm in action: