- There are two stages of flatworms; there is the adult flatworm and the larva. The host of the adult is called the main host and the host of the larvae is the alternate host. Most flatworms are found in third world countries, they are also found where sanitary conditions are very low and standards for disposal are not high.
- These species occur in soil, moist sand, leaf litter, mud, under rocks, and on vegetation. Some have been found in pools in the desert and in caves. Cave-dwelling species tend to show loss of eyes and pigment.