In biology/ecology, parasitism is a non-mutual symbiotic relationship between species, where one species, the parasite, benefits at the expense of the other, the host. Traditionally parasite (in biological usage) referred primarily to organisms visible to the naked eye, or macroparasites (such as helminths). Parasite can include microparasites, which are typically smaller, such as protozoa, viruses, and bacteria. Examples of parasites include the plants mistletoe and cuscuta, and animals such as hookworms.