The earthworms of the family Lumbricidae are mainly free-living terrestrial animals living in soil, leaf litter, under stones, etc. They tend to inhabit wetter, more heavily vegetated areas.
An interesting thing about these worms is that they breath through their skin, and do not have lungs. For this to happen, they need to keep their skins moist, but at the same time protected from pathogens that seek to attack through this wet covering. If you pick up these worms, you will soon find their method of protection as you find a mucus - like substance on your hands.