Parasitism is a symbiotic mechanism where the parasite lives in or on the host and causes harm although the parasite is structurally adapted to this way of life. The survival mechanism of human endoparasites such as liverflukes illustrates parasitism as a way of life. The parasites latches onto the host's liver and feeds on its bile and tissues. Similarly, Oceanic parasites such as whale lice snags onto whales for food and transportation. They feed primarily on algae that collect on the whale's skin, but also attack open wounds and damaged tissue. Moreover, plant parasites such as aphids feed on plant sap, usually too much plant sap for the wellbeing of the plant they infest. Ectoparasites such as horseflies are fond of feeding on domesticated animals. Although parasitism is unpleasant, it is a fundamental part of nature.