Parasitism

Parasitism, scored (+, --), is a harmful interspecific interaction in which one partner, the parasite, benefits at the direct expense of the other, its host — drawing shelter, food and protection from the host while the host itself is harmed by the relationship, and parasites typically evolve specific adaptations that let them exploit their particular host efficiently. Parasites are classified by their taxonomic origin (viral parasites infecting plants or animals; microbial parasites such as bacteria, protozoa or fungi; phytoparasites that parasitise plants; and zooparasites such as parasitic flatworms, nematodes and arthropods that parasitise animals) and by where they live relative to the host's body: ectoparasites live on or attach to the host's external surface (head lice and leeches are examples), while endoparasites live inside the host's body — often in the alimentary tract, body cavities, specific organs, or blood — with Ascaris and tapeworms as classic examples. Parasites are further classed by the duration of their parasitic phase: temporary parasites spend only part of their life cycle attached to a host, as with the glochidium larva of the freshwater musse …