Lizards, centipedes, frogs, toads, turtles, skunks, gophers, snakes, moles and birds all eat worms. People who spray insecticides on the earth are the biggest danger to earthworms. Poisons can kill many acres of worms at one time. There can be over a million earthworms in one acre of land. Their burrows are flooded and the water is no longer fresh.
Worms are night animals.
There is a danger of their drying out during the day. Yes, if you put a worm on its top side it will turn over onto its bottom side. The bottom side is usually a little lighter in color. It can't do much by itself. But working together with the thousands of other earthworms usually found in a garden, they will mix the soil, supply it with air, and fertilize it.