Flatworms, or land planarians, are in a family of predators that attack earthworms, snails, slugs and insects. Flatworms secrete a substance from their glands that allows them to externally digest their prey. They are native to China but have spread throughout the world in soil and plants. Flatworms are primarily nocturnal and if cut in pieces, each piece can regenerate and grow to be a new flatworm. Flatworms can be detrimental to gardens as they can wipe out all the earthworms, and some species have become invasive in wild habitats of the Pacific Islands.