Organisms that live in or upon the body of a host organism and are metabolically dependent on the host for completion of their life cycle. Parasites may be plants, animals, viruses, bacteria, or fungi. Parasites feed either on their host directly or upon its surplus fluids. Some parasites, known as endoparasites, live inside their host, while ectoparasites live on the outside of their host. Organisms in which parasites reach maturity are called definitive hosts, and hosts harboring parasite stages are called intermediate hosts. Organisms which spread parasite stages between hosts are known as vectors. Full-time, or obligatory, parasites have an absolute dependence on their hosts. Examples of this type are viruses, which can only live and multiply inside living cells, and tapeworms, which can only live and multiply inside other species. Part-time, or facultative, parasites, such as wood ticks, have parasitic and free-living stages in their life cycle...